Reptiles

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Reptiles
Fossil range: Carboniferous - Recent

Eastern Hermann's Tortoise

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Sauropsida Goodrich, 1916

Orders

Procolophonia (extinct)
Testudines
Araeoscelidia (extinct)
Avicephala (extinct)
Younginiformes (extinct)
Sauropterygia
- Ichthyosauria (extinct)
- Placodontia (extinct)
- Nothosauria (extinct)
- Plesiosauria (extinct)
Sphenodontia
Squamata
Prolacertiformes (extinct)
Archosauria
- Crurotarsi
  - Order Aetosauria
  - Order Phytosauria
  - Order Rauisuchia
  - Order Crocodilia
- Ornithodira
  - Pterosauria (extinct)
  - Marasuchus (extinct)
  - Dinosauria (extinct)
    - Order Saurischia
    - Order Ornithischia

Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane. Today they are represented by four surviving orders:

Crocodilia (crocodiles, caimans and alligators): 23 species
Sphenodontia (tuataras from New Zealand): 2 species
Squamata (lizards, snakes and amphisbaenids ("worm-lizards")): approximately 7,600 species
Testudines (turtles): approximately 300 species

Reptiles are found on every continent except for Antarctica, although their main distribution comprises the tropics and subtropics. Though all cellular metabolism produces some heat, most modern species of reptiles do not generate enough to maintain a constant body temperature and are thus referred to as "cold-blooded" or ectothermic (the Leatherback Sea Turtle is an exception). Instead, they rely on gathering and losing heat from the environment to regulate their internal temperature, e.g, by moving between sun and shade, or by preferential circulation — moving warmed blood into the body core, while pushing cool blood to the periphery. In their natural habitats, most species are adept at this, and can ususally maintain core body temperatures within a fairly narrow range, comparable to that of mammals and birds, the two surviving groups of "warm-blooded" animals. While this lack of adequate internal heating imposes costs relative to temperature regulation through behavior, it also provides a large benefit by allowing reptiles to survive on much less food than comparably-sized mammals and birds, who burn much of their food for warmth. While warm-blooded animals move faster in general, an attacking lizard, snake or crocodile moves very quickly.

Except for a few members of the Testudines, all reptiles are covered by scales.

Most reptile species are oviparous (egg-laying). Many species of squamates, however, are capable of giving live birth. This is achieved, either through ovoviviparity (egg retention), or viviparity (babies born without use of calcified eggs). Many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals (Pianka & Vitt, 2003 pgs: 116-118). They often provide considerable initial care for their hatchlings.

by Nicolae Sfetcu

This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Reptile

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Classification of reptiles

Reptiles are a paraphyletic group. The group can be made monophyletic by including the birds (Aves).

From the classical standpoint, reptiles included all the amniotes except birds and mammals. Thus reptiles were defined as the set of animals that includes crocodiles, alligators, tuatara, lizards, snakes, amphisbaenians and turtles, grouped together as the class Reptilia (Latin repere, "to creep"). This is still the usual definition of the term.

However, in recent years, many taxonomists have begun to insist that taxa should be monophyletic, that is, groups should include all descendants of a particular form. The reptiles as defined above would be paraphyletic, since they exclude both birds and mammals, although these also developed from the original reptile. Colin Tudge writes:

Mammals are a clade, and therefore the cladists are happy to acknowledge the traditional taxon Mammalia; and birds, too, are a clade, universally ascribed to the formal taxon Aves. Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class reptilia is not a clade. It is just a section of the clade Amniota: the section that is left after the Mammalia and Aves have been hived off. It cannot be defined by synamorphies, as is the proper way. It is instead defined by a combination of the features it has and the features it lacks: reptiles are the amniotes that lack fur or feathers. At best, the cladists suggest, we could say that the traditional Reptila are 'non-avian, non-mammalian amniotes'. (Tudge, p.85)

By the same token, the traditional class Amphibia becomes Amphibia*, because some ancient amphibian or other gave rise to all the amniotes; and the phylum Crustacea becomes Crustacea*, because it may have given rise to the insects and myriapods (centipedes and millipedes). If we believe, as some (but not all) zoologists do, that myriapods gave rise to insects, then they should be called Myriapoda*....by this convention Reptilia without an asterisk is synonymous with Amniota, and includes birds and mammals, whereas Reptilia* means non-avian, non-mammalian amniotes. (Tudge, p.85)

Recent college-level references, such as Benton (2004) [1], offer another compromise by applying traditional ranks to accepted phylogenetic relationships. In this case, reptiles belong to the class Sauropsida, and mammal-like reptiles to the class Synapsida, with birds and mammals separated into their own traditional classes.

Reptile Groups

Class Sauropsida
- Family Captorhinidae (extinct)
- Family Protorothyrididae - Hylonomus (extinct)
- Subclass Anapsida
  - Family Mesosauridae (extinct)
    Order Procolophonia - incl. Pareiasaurs (extinct)
    ?Order Testudines - Turtles
- Subclass Diapsida
  - Superorder Ichthyopterygia - Ichthyosaurs (extinct)
  - Infraclass Lepidosauromorpha
    - Superorder Sauropterygia - Plesiosaurs (extinct)
    - Superorder Lepidosauria
      - Order Sphenodontia - Tuatara
      - Order Squamata - Lizards & Snakes
  - Infraclass Archosauromorpha
    - Order Crocodilia - Crocodilians
    - Order Pterosauria - Pterodactyls (extinct)
    - Superorder Dinosauria - Dinosaurs
      - Class Aves - Birds

Evolution of the reptiles

Young American Alligator Georgetown, South Carolina

Hylonomus is the oldest-known reptile, and was about 8 to 12 inches (20 to 30 cm) long. Westlothiana has been suggested as the oldest reptile, but is for the moment considered to be more related to amphibians than amniotes. Petrolacosaurus and Mesosaurus are other examples. The first true "reptiles" (Sauropsids) are categorized as Anapsids, having a solid skull with holes only for nose, eyes, spinal cord, etc. Turtles are believed by some to be surviving Anapsids, as they also share this skull structure; but this point has become contentious lately, with some arguing that turtles reverted to this primitive state in order to improve their armor. Both sides have strong evidence, and the conflict has yet to be resolved.

Shortly after the first reptiles, two branches split off, one leading to the Anapsids, which did not develop holes in their skulls. The other group, Diapsida, possessed a pair of holes in their skulls behind the eyes, along with a second pair located higher on the skull. The Diapsida split yet again into two lineages, the lepidosaurs (which contain modern snakes, lizards and tuataras, as well as, debatably, the extinct sea reptiles of the Mesozoic) and the archosaurs (today represented by only crocodilians and birds, but also containing pterosaurs and dinosaurs).

The earliest, solid-skulled amniotes also gave rise to a separate line, the Synapsida. Synapsids developed a pair of holes in their skulls behind the eyes (similar to the diapsids), which were used to both lighten the skull and increase the space for jaw muscles. The synapsids eventually evolved into mammals, and are often referred to as mammal-like reptiles, though they are not true members of the class Sauropsida.

Systems

Circulatory

Thermographic image of a monitor lizard.

Most reptiles have closed circulation via a three-chamber heart consisting of two atria and one, variably-partitioned ventricle. There is usually one pair of aortic arches. In spite of this, due to the fluid dynamics of blood flow through the heart, there is little mixing of oxygenated and deoxygenated blood in the three-chamber heart. Furthermore, the blood flow can be altered to shunt either deoxygenated blood to the body or oxygenated blood to the lungs, which gives the animal greater control over its blood flow, allowing more effective thermoregulation and longer diving times for aquatic species. There are some interesting exceptions among reptiles. For instance, crocodilians have an incredibly complicated four-chamber heart that is capable of becoming a functionally three-chamber heart during dives (Mazzotti, 1989 pg 47). Also, it has been discovered that some snake and lizard species (e.g., monitor lizards and pythons) have three-chamber hearts that become functional four-chamber hearts during contraction. This is made possible by a muscular ridge that subdivides the ventricle during ventricular diastole and completely divides it during ventricular systole. Because of this ridge, some of these squamates are capable of producing ventricular pressure differentials that are equivalent to those seen in mammalian and avian hearts (Wang et al, 2003).

Respiratory

All reptiles breathe using lungs. Aquatic turtles have developed more permeable skin, and even gills in their anal region, for some species (Orenstein, 2001). Even with these adaptations, breathing is never fully accomplished without lungs. Lung ventilation is accomplished differently in each main reptile group. In squamates the lungs are ventilated almost exclusively by the axial musculature. This is also the same musculature that is used during locomotion. Because of this constraint, most squamates are forced to hold their breath during intense runs. Some, however, have found a way around it. Varanids, and a few other lizard species, employ buccal pumping as a complement to their normal "axial breathing." This allows the animals to completely fill their lungs during intense locomotion, and thus remain aerobically active for a long time. Tegu lizards are known to possess a proto-diaphragm, which separates the pulmonary cavity from the visceral cavity. While not actually capable of movement, it does allow for greater lung inflation, by taking the weight of the viscera off the lungs (Klein et al, 2003). Crocodilians actually have a muscular diaphragm that is analogous to the mammalian diaphragm. The difference is that the muscles for the crocodilian diaphragm pull the pubis (part of the pelvis, which is movable in crocodilians) back, which brings the liver down, thus freeing space for the lungs to expand. This type of diaphragmatic setup has been referred to as the "hepatic piston."

How Turtles & Tortoises breathe has been the subject of much study. To date, only a few species have been studied thoroughly enough to get an idea of how turtles do it. The results indicate that turtles & tortoises have found a variety of solutions to this problem. The problem is that most turtle shells are rigid and do not allow for the type of expansion and contraction that other amniotes use to ventilate their lungs. Some turtles such as the Indian flapshell (Lissemys punctata) have a sheet of muscle that envelopes the lungs. When it contracts, the turtle can exhale. When at rest, the turtle can retract the limbs into the body cavity and force air out of the lungs. When the turtle protracts its limbs, the pressure inside the lungs is reduced, and the turtle can suck air in. Turtle lungs are attached to the inside of the top of the shell (carapace), with the bottom of the lungs attached (via connective tissue) to the rest of the viscera. By using a series of special muscles (roughly equivalent to a[diaphragm]), turtles are capable of pushing their viscera up and down, resulting in effective respiration, since many of these muscles have attachment points in conjunction with their forelimbs (indeed, many of the muscles expand into the limb pockets during contraction). Breathing during locomotion has been studied in three species, and they show different patterns. Adult female green sea turtles do not breathe as they crutch along their nesting beaches. They hold their breath during terrestrial locomotion and breathe in bouts as they rest. North American box turtles breathe continuously during locomotion, and the ventilation cycle is not coordinated with the limb movements (Landberg et al., 2003). They are probably using their abdominal muscles to breathe during locomotion. The last species to have been studied is red-eared sliders, which also breathe during locomotion, but they had smaller breaths during locomotion than during small pauses between locomotor bouts, indicating that there may be mechanical interference between the limb movements and the breathing apparatus. Box turtles have also been observed to breathe while completely sealed up inside their shells (ibid).

Most reptiles lack a secondary palate, meaning that they must hold their breath while swallowing. Crocodilians have evolved a bony secondary palate that allows them to continue breathing while remaining submerged (and protect their brains from getting kicked in by struggling prey). Skinks (family Scincidae) also have evolved a bony secondary palate, to varying degrees. Snakes took a different approach and extended their trachea instead. Their tracheal extension sticks out like a fleshy straw, and allows these animals to swallow large prey without suffering from asphyxiation.

Also, crocodiles are known to cry while eating. Many myths and folklore have grown around this astonishing fact, such as that the crocodile feels guilty for eating, but in truth, the crocodile cries to release fluid from its body, to make room for oxygen. This is also due to the fact that the crocodile's nasal cavity (nose) is exceptionally small.

Excretion

Excretion is performed mainly by two small kidneys. In diapsids uric acid is the main nitrogenous waste product; turtles, like mammals, mainly excrete urea. Unlike the kidneys of mammals and birds, reptile kidneys are unable to produce liquid urine more concentrated than their body fluid. This is because they lack a specialised structure present in the nephrons of birds and mammals, called a Loop of Henle. Because of this, many reptiles use the colon and cloaca to aid in the reabsorption of water. Some are also able to take up water stored in the bladder. Excess salts are also excreted by nasal and lingual salt-glands in some reptiles.

Nervous

Advanced nervous system compared to amphibians. They have twelve pairs of cranial nerves.

Sexual

Most reptiles reproduce sexually. All male reptiles except turtles and tortoises have a twin tube like sexual organ called the hemipenes. Turtles and tortoises have a single penis. All testudines lay eggs, none are live bearing as some lizard and snakes are. All reproductive activity occurs with the cloaca, the single exit/entrance at the base of the tail where waste and reproduction happens.

Asexual reproduction has been identified in squamates in six families of lizards and one snake. In some species of squamates, a population of females are able to produce a unisexual diploid clone of the mother. This asexual reproduction called parthenogenesis occurs in several species of gecko, and is particularly widespread in the teiids (especially Aspidocelis) and lacertids (Lacerta). Parthenogentic species are also suspected to occur among chameleons, agamids, xantusiids, and typhlopids.

Amniotic eggs are covered with leathery or calcareous shells. An amnion, chorion and allantois are present during embryonic life. There are no larval stages of development.

References

Colin Tudge (2000). The Variety of Life. Oxford University Press. ISBN 0198604262.

Benton, M. J. (2004), Vertebrate Paleontology, 3rd ed. Blackwell Science Ltd.

Pianka, Eric; Vitt, Laurie (2003). Lizards Windows to the Evolution of Diversity. University of California Press, 116-118. ISBN 0-520-23401-4.

Mazzotti, Frank; Ross, Charles (ed) (1989). "Structure And Function" Crocodiles and Alligators. Facts on File. ISBN 0-8160-2174-0.

Wang, Tobias; Altimiras, Jordi; Klein, Wilfried; Axelsson, Michael (2003). Ventricular haemodynamics in Python molurus: separation of pulmonary and systemic pressures. The Journal of Experimental Biology 206: 4242-4245.

Klein, Wilfried; Abe, Augusto; Andrade, Denis; Perry, Steven (2003). Structure of the posthepatic septum and its influence on visceral topology in the tegu lizard, Tupinambis merianae (Teidae: Reptilia). Journal of Morphology 258 (2): 151-157.

Orenstein, Ronald (2001). Turtles, Tortoises & Terrapins: Survivors in Armor. Firefly Books. ISBN 1-55209-605-X.

Landberg, Tobias; Mailhot, Jeffrey; Brainerd, Elizabeth (2003). Lung ventilation during treadmill locomotion in a terrestrial turtle, Terrapene carolina. Journal of Experimental Biology 206 (19): 3391-3404.

Pough, Harvey; Janis, Christine; Heiser, John (2005). Vertebrate Life. Pearson Prentice Hall. ISBN 0-13-145310-6.

Laurin, Michel and Gauthier, Jacques A.: Diapsida. Lizards, Sphenodon, crocodylians, birds, and their extinct relatives, Version 22 June 2000; part of The Tree of Life Web Project

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Extant reptiles

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50 Pounds of Reptile Fun

This is a

list of extant reptiles

by family, spanning three subclasses.

Subclass Anapsida

Order Testudines - Turtles

Suborder Cryptodira
- Family Chelydridae - Snapping Turtles
  Family Emydidae - Pond Turtles and Box Turtles
  Family Testudinidae - Tortoises
  Family Geoemydidae - Asian River Turtles and Allies
  Family Carettochelyidae - Pignose Turtles
  Family Trionychidae - Softshell Turtles
  Family Dermatemydidae - River Turtles
  Family Kinosternidae - Mud Turtles
  Family Cheloniidae - Sea Turtles
  Family Dermochelyidae - Leatherback Turtles
Suborder Pleurodira
- Family Chelidae - Austro-American Sideneck Turtles
  Family Pelomedusidae - Afro-American Sideneck Turtles
  Family Podocnemididae - Madagascan Big-headed Turtles and American Sideneck River Turtles

Subclass Lepidosauria

Order Rhynchocephalia - Tuataras

Suborder Sphenodontida
- Family Sphenodontidae

Order Squamata - Scaled reptiles

Suborder Sauria
- Family Agamidae - Agamas
- Family Chamaeleonidae - Chameleons
- Family Iguanidae
  - Subfamily Corytophaninae - Casquehead Lizard
    Subfamily Crotaphytinae - Collared and Leopard Lizards
    Subfamily Hoplocercinae - Wood lizards
    Subfamily Iguaninae - Iguanas
    Subfamily Leiocephalinae
    Subfamily Leiosaurinae
    Subfamily Liolaeminae
    Subfamily Oplurinae - Madagascar iguanids
    Subfamily Phrynosomatinae - Horned Lizards
    Subfamily Polychrotinae - Anoles
    Subfamily Tropidurinae - Neotropical Ground Lizards
- Family Gekkonidae - Geckoes
  Family Pygopodidae - Legless lizards
  Family Dibamidae - Blind Lizards
  Family Cordylidae - Spinytail Lizards
  Family Gerrhosauridae - Plated Lizards
  Family Gymnophthalmidae - Spectacled Lizards
  Family Teiidae - Whiptails and Tegus
  Family Lacertidae - Lacertids
  Family Scincidae - Skinks
  Family Xantusiidae - Night Lizards
  Family Anguidae - Glass Lizards
  Family Anniellidae - American legless lizards
  Family Xenosauridae - Knob-scaled Lizards
  Family Helodermatidae - Gila Monsters
  Family Lanthanotidae - Earless Monitor lizards
  Family Varanidae - Monitor Lizards
Suborder Amphisbaenia
- Family Amphisbaenidae - Worm Lizards
  Family Trogonophidae - Shorthead Worm Lizards
  Family Bipedidae - Two-legged Worm Lizards
Suborder Ophidia - Snakes
- Family Anomalepidae - Dawn Blind Snakes
  Family Typhlopidae - Blind Snakes
  Family Leptotyphlopidae - Slender Blind Snakes
  Family Aniliidae - Pipe Snakes
  Family Anomochilidae - Dwarf pipe snakes
  Family Boidae - Boas and Pythons
  Family Bolyeridae - Round Island Boas
  Family Cylindrophiidae - Asian pipe snakes
  Family Loxocemidae - Mexican Burrowing Pythons
  Family Tropidophiidae - Dwarf boas
  Family Uropeltidae - Shield-tail Snakes
  Family Xenopeltidae - Sunbeam Snakes
  Family Acrochordidae - File Snakes
  Family Atractaspididae - Mole Vipers
  Family Colubridae - Colubrids
  Family Elapidae - Coral Snakes and Sea Snakes
- Family Viperidae - Vipers
  - Subfamily Azemiopinae - Fea's viper
    Subfamily Causinae - Night adders
    Subfamily Crotalinae - Pit vipers
    Subfamily Viperinae - Pitless vipers

Subclass Archosauria

Order Crocodylia - Crocodiles

Suborder Eusuchia
- Family Crocodylidae

Tuatara

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reptiles

scientific classification

Male tuatara

Tuatara
Conservation status: Vulnerable

Male tuatara

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Order:	Sphenodontia
Family:	Sphenodontidae
Genus:	Sphenodon Gray, 1831

Species

Sphenodon punctatus (Gray, 1842)
Sphenodon guntheri Buller, 1877
Sphenodon diversum (extinct)

The tuatara is a reptile of the family Sphenodontidae, endemic to New Zealand. The two species are the only surviving members of the Sphenodontians. The tuataras resemble lizards, but are equally related to lizards and snakes, which are their closest living relatives. For this reason, they are of great interest in the study of the evolution of lizards and snakes, and for the reconstruction of the appearance and habits of the earliest diapsids (the group that additionally includes birds and crocodiles).

The tuatara has been classified as an endangered species since 1895. Tuataras, like many of New Zealand's native animals, are threatened by habitat loss and introduced species, such as mustelids and rats. They were extinct on the mainland, with the remaining populations confined to 32 offshore islands,[1] until the first mainland release into the heavily fenced and monitored Karori Wildlife Sanctuary in 2005.

References

Cited references

New Zealand Department of Conservation - Tuatara page
Cree, Alison. 2002. Tuatara. In: Halliday, Tim and Adler, Kraig (eds.), The new encyclopedia of reptiles and amphibians, Oxford University Press, Oxford, pp. 210-211. ISBN 0-19-852507-9
Fraser, Nicholas; Sues, Hans-Dieter; (eds) (1994). "Phylogeny" In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cambridge University Press. ISBN 0-521-45242-2.
Lepidosauromorpha
Fact Sheet on BBC website
New Zealand Ecology--Living Fossils
Wu, Xiao-Chun (1994). "Late Triassic-Early Jurassic sphenodontians from China and the phylogeny of the Sphenodontia" in Nicholas Fraser & Hans-Dieter Sues (eds) In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cambridge University Press. ISBN 0-521-45242-2.
Tuatara on Kiwi Conservation Club
Kaplan, Melissa (2003-09-06). Reptile Hearing. Melissa Kaplan's Herp Care Collection
Animal Diversity Web: Tuatara - Habitat
Thompson MB and Daugherty CH (1998). "Metabolism of tuatara, Sphenodon punctatus". Comparative biochemistry and physiology A 119: 519-522.
Cree et al (1992). "Reproductive cycles of male and female tuatara (Sphenodon punctatus) on Stephens Island, New Zealand". Journal of Zoology 226: 199-217.
C. Gand, J.C. Gillingham and D.L. Clark (1984). "Courtship, mating and male combat in Tuatara, Sphenodon punctatus". Journal of Herpetology 18(2): 194-197.
Tuatara Sex Debate
http://www.waitangi-tribunal.govt.nz/doclibrary/public/wai262/matauranga_maori/Chapt06.pdf
Five Cents for the Tuatara

General references

McKintyre, Mary (1997). Conservation of the Tuatara. Victoria University Press. ISBN 0-86473-303-8.
Parkinson, Brian (2000). The Tuatara. Reed Children’s Books. ISBN 1-86948-831-8.
Lutz, Dick (2005). Tuatara: A Living Fossil. DIMI PRESS. ISBN 0-931625-43-2.

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Tuatara taxonomy and evolution

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Tuatara - Sphenodon Punctatus

Tuataras, and their sister group Squamata (which includes lizards, snakes and amphisbaenians), belong to the superorder Lepidosauria, the only surviving taxon within Lepidosauromorpha. Squamates and tuataras both show caudal autotomy, loss of the tail-tip when threatened, and have a transverse cloacal slit. The origin of the tuatara probably lies close to the split between the Lepidosauromorpha and the Archosauromorpha. Though tuatara resemble lizards, the similarity is mostly superficial, since the family has several characteristics unique among reptiles. The typical lizard shape is very common for the early amniotes; the oldest known fossil of a reptile, the Hylonomus, resembles a modern lizard.

Tuataras were originally classified as lizards in 1831 when the British Museum received a skull. The species remained misclassified until 1867, when Albert Günther of the British Museum noted features similar to birds, turtles and crocodiles. He proposed the order Rhynchocephalia (meaning "beak head") for the tuatara and its fossil relatives.

During the years since the inception of the Rhynchocephalia, many disparately related species have been added to this order. This has resulted in turning the rhynchocephalia into what taxonomists call a "wastebin taxon". Sphenodontia was proposed by Williston in 1925. Now, most authors prefer to use the more exclusive order name of Sphenodontia for the tuatara and its closest living relatives.

Sphenodon punctatus, drawing from unknown period

There are two extant species of tuatara: Sphenodon punctatus and the much rarer Sphenodon guntheri, or Brothers Island tuatara, which is confined to The Brothers Islands in Cook Strait. The Brothers Island tuatara have olive skin with yellowish patches. Sphenodon punctatus has two subspecies: the Cook Strait tuatara (unnamed subspecies), which lives on other islands in and near Cook Strait, and the northern tuatara (Sphenodon punctatus punctatus), which lives on the Bay of Plenty, and some islands further north.

Tuataras have been referred to as living fossils This means that they have remained mostly unchanged throughout their entire history, which is approximately 200 million years. However, taxonomic work on Sphenodontia has shown that this group has undergone a variety of changes throughout the Mesozoic. Many of the niches normally associated with lizards were instead held by sphenodontians. There was even a successful group of aquatic sphenodontians known as pleurosaurs, which differed markedly from living tuataras. Tuataras show cold weather adaptations that allow them to thrive on the islands of New Zealand; these adaptations are probably unique to tuataras and not present in extinct sphenodontians, which lived in much warmer climates.

This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Tuatara taxonomy and evolution

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Cladogram showing relationships of extant members of the Sauria. Numbered items are:
1. Tuatara
2. Lizards
3. Snakes
4. Crocodiles
5. Birds
"Lizards" are paraphyletic. Branch lengths do not indicate divergence times.

Tuataras, and their sister group Squamata (which includes lizards, snakes and amphisbaenians), belong to the superorder Lepidosauria, the only surviving taxon within Lepidosauromorpha. Squamates and tuataras both show caudal autotomy, loss of the tail-tip when threatened, and have a transverse cloacal slit.[2] The origin of the tuatara probably lies close to the split between the Lepidosauromorpha and the Archosauromorpha. Though tuatara resemble lizards, the similarity is mostly superficial, since the family has several characteristics unique among reptiles. The typical lizard shape is very common for the early amniotes; the oldest known fossil of a reptile, the Hylonomus, resembles a modern lizard.

During the years since the inception of the Rhynchocephalia, many disparately related species have been added to this order. This has resulted in turning the rhynchocephalia into what taxonomists call a "wastebin taxon".[3] Sphenodontia was proposed by Williston in 1925.^[1] Now, most authors prefer to use the more exclusive order name of Sphenodontia for the tuatara and its closest living relatives.^[2]

There are two extant species of tuatara: Sphenodon punctatus and the much rarer Sphenodon guntheri, or Brothers Island tuatara, which is confined to The Brothers Islands in Cook Strait.[5] The Brothers Island tuatara have olive skin with yellowish patches. Sphenodon punctatus has two subspecies: the Cook Strait tuatara (unnamed subspecies), which lives on other islands in and near Cook Strait, and the northern tuatara (Sphenodon punctatus punctatus), which lives on the Bay of Plenty, and some islands further north.^[3]

Tuataras have been referred to as living fossils [6] This means that they have remained mostly unchanged throughout their entire history, which is approximately 200 million years.[6] However, taxonomic work[7] on Sphenodontia has shown that this group has undergone a variety of changes throughout the Mesozoic. Many of the niches normally associated with lizards were instead held by sphenodontians. There was even a successful group of aquatic sphenodontians known as pleurosaurs, which differed markedly from living tuataras. Tuataras show cold weather adaptations that allow them to thrive on the islands of New Zealand; these adaptations are probably unique to tuataras and not present in extinct sphenodontians, which lived in much warmer climates.

Cited references

^ ^a ^b Fraser, Nicholas; Sues, Hans-Dieter; (eds) (1994). "Phylogeny" In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cambridge University Press. ISBN 0-521-45242-2.
^ Lepidosauromorpha. Retrieved on 2006-07-27.
^ ^a ^b ^c New Zealand Department of Conservation - Tuatara page. Retrieved on 2006-02-28.

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Physical description of tuatara

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Male tuatara

The tuatara is considered the most unspecialised living amniote; the brain and mode of locomotion resemble that of amphibians and the heart is more primitive than any other reptile. Adults are about 50 centimetres (20 in) long and weigh between 0.5 and 1 kilogram (1.1-2.2 lb). They display sexual dimorphism, as the males are larger, weighing up to 1 kilogram (2.2 lb), almost twice the weight reached by females. The spiny crest on their back, made of triangular soft folds of skin, is bigger in males than in females, and can be stiffened for display. The male abdomen is narrower than the female's. The tuatara's color ranges from olive green to brown to orange-red, and it can change color over its lifetime. It sheds its skin once a year.

Skull

In the course of evolution, the skull has been modified in most diapsids from the original version evident in the fossil record. However, in the tuatara, all the original features are preserved: it has two openings (temporal fenestrae) on each side of the skull, with complete arches. In addition, in the tuatara, the upper jaw is firmly attached to the skull. This makes for a very rigid, inflexible construction.
Testudines (turtle and tortoise) skulls were once believed to be the most primitive among amniotes, but newer research suggests this is not the case, as they might have lost the temporal holes in the skull secondarily rather than never having had them.

Tuatara teeth In the tuatara, two rows of teeth in the upper jaw close over one row in the lower jaw

The tip of the upper jaw is beaklike and separated from the remainder of the jaw by a notch. There is a single row of teeth in the lower jaw and a double row in the upper jaw, with the bottom row fitting perfectly between the two upper rows when the mouth is closed. This is a tooth arrangement not seen in any other reptiles; although most snakes also have a double row of teeth in their upper jaw, their arrangement and function is different from the tuatara's. The jaws, joined by ligament, chew with backwards and forwards movements combined with a shearing up and down action. The force of the bite is suitable for shearing chitin and bone.[2] The double-row arrangement provides a self-sharpening mechanism. The tuatara's teeth are not replaced, since they are not separate structures like real teeth, but sharp projections of the jaw bone. As their teeth wear down, older tuataras have to switch to softer prey such as earthworms, larvae, and slugs, and eventually have to chew their food between smooth jaw bones.

Sensory organs

In tuataras, both eyes can focus independently, and are specialized with a "duplex retina" that contains two types of visual cells for vision by both day and night , and a tapetum lucidum which reflects on to the retina to enhance vision at night. There is also a third eyelid on each eye, the nictitating membrane.

Tuatara at Hamilton Zoo

The tuatara has a third eye on the top of its head called the parietal eye. It has its own lens, cornea, retina with rod-like structures and degenerated nerve connection to the brain, suggesting it evolved from a real eye. The parietal eye is only visible in hatchlings, which have a translucent patch at the top centre of the skull. After four to six months it becomes covered with opaque scales and pigment.[2] Its purpose is unknown, but it may be useful in absorbing ultraviolet rays to manufacture vitamin D, as well as to determine light/dark cycles, and help with thermoregulation. Of all extant tetrapods, the parietal eye is most pronounced in the tuatara.

Together with turtles, the tuatara has the most primitive hearing organs among the amniotes. There is no eardrum, and the middle ear cavity is filled with loose tissue, mostly adipose tissue. The stapes comes into contact with the quadrate (which is immovable) as well as the hyoid and squamosal. The hair cells are unspecialized, innervated by both afferent and efferent nerve fibers, and respond only to low frequencies. Even though the hearing organs are poorly developed and primitive with no visible external ears, they can still show a frequency response from 100-800 Hz, with peak sensitivity of 40 dB at 200 Hz.

Spine and ribs

Adult tuatara on a rock

The tuatara spine is made up of hour-glass shaped amphicoelous vertebrae, concave both before and behind. This is the usual condition of fish vertebrae and some amphibians, but is unique to tuataras within the amniotes.

The tuatara has gastralia, rib-like bones also called gastric or abdominal ribs, the presumed ancestral trait of diapsids. It is found in some lizards (in lizards they are mostly made of cartilage), crocodiles and the tuatara, and are not attached to the spine or thoracic ribs.

The real ribs are small projections, with small, hooked bones, called uncinate processes, found on the rear of each rib. This feature is also present in birds. The tuatara is the only living tetrapod with well developed gastralia and uncinate processes.

In the early tetrapods, the gastralia and ribs with uncinate processes, together with bony elements such as bony plates in the skin (osteoderms) and clavicles (collar bone), would have formed a sort of exo-skeleton around the body, protecting the belly and helped to hold in the guts and inner organs. These anatomical details most likely evolved from structures involved in locomotion even before the vertebrates migrated onto land. It is also possible the gastralia were involved in the breathing process in primitive and extinct amphibians and reptiles. The pelvis and shoulder girdles are arranged differently than in lizards, as is the case with other parts of the internal anatomy and its scales.

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Natural history of tuatara

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Tuatara at the Karori Wildlife Sanctuary

Adult tuataras are terrestrial and nocturnal reptiles, though they will often bask in the sun to warm their bodies. Hatchlings hide under logs and stones, and are diurnal, likely because adults are cannibalistic. Tuataras survive in temperatures much lower than those tolerated by most reptiles, and hibernate during winter. They can maintain normal activities at temperatures as low as 7° C, while temperatures over 28° C are generally fatal. The optimal body temperature for the tuatara is from 16 to 21° C, the lowest of any reptile.[10] The body temperature of tuatara is lower than that of other reptiles ranging from 5.2–11.2° C over a day, whereas most reptiles have body temperatures around 20° C.[11] The low body temperature results in a slower metabolism.

Burrowing seabirds such as petrels, prions and shearwaters share the tuataras' island habitat during the bird's nesting season. The tuataras use the bird's burrows for shelter when available, or dig their own. The seabirds' guano helps to maintain invertebrate populations that tuataras predominantly prey on; including beetles, crickets and spiders. Their diet also consists of frogs, lizards and bird's eggs and chicks. Seabirds may provide beneficial fatty acids.

Tuatara juvenile

Tuataras reproduce very slowly; taking ten years to reach sexual maturity. Mating occurs in midsummer; females mate and lay eggs once every four years. During courtship, a male makes his skin darker, raises his crests and parades toward the female. He circles himself around the female while slowly walking with stiffened legs. The female will either submit, and allow the male to mount her, or retreat to her burrow. Males do not have a penis; they reproduce by the male lifting the tail of the female and placing his vent over hers. The sperm is then transferred into the female.

Tuatara eggs have a soft, parchment-like shell. It takes the females between one and three years to provide eggs with yolk, and up to seven months to form the shell. It then takes between 12 and 15 months from copulation to hatching. This means reproduction occurs at 2 to 5 year intervals, the slowest in any reptile. The sex of a hatchling depends on the temperature of the egg, with warmer eggs tending to produce male tuataras, and cooler eggs producing females. Eggs incubated at 21° C have an equal chance of being male or female. However, at 22° C, 80% are likely to be males, and at 20° C, 80% are likely to be females; at 18° C all hatchlings will be females. There is some evidence that sex determination in tuataras is determined by both genetic and environmental factors.

Tuataras probably have the slowest growth rates of any reptile, continuing to grow larger for the first 35 years of their lives. The average lifespan is about 60 years, but they can live to be over 100 years old.

Conservation status

Tuataras, like many native New Zealand animals, are threatened by habitat loss, and introduced species such as mustelids and rats. They were long confined to 32 offshore islands free of mammals.[1] A mainland release occurred in 2005 in the heavily fenced and monitored Karori Wildlife Sanctuary.

Sphenodon guntheri is present naturally on one small island with a population of approximately 400, and has been reintroduced to two others. Sphenodon punctatus naturally occurs on 29 islands and its population is estimated to be over 60,000 individuals.

There are several Tuatara breeding programmes within New Zealand. Southland Museum and Art Gallery in Invercargill, was the first to have a tuatara breeding programme; they breed Sphenodon punctatus. Hamilton Zoo and Wellington Zoo also breed tuataras for release into the wild. The Victoria University of Wellington maintains a research programme into the captive breeding of tuataras, and the National Wildlife Centre at Pukaha Mount Bruce keeps a pair and juvenile. The WildNZ Trust has a tuatara breeding enclosure at Ruawai.

Etymology and cultural significance

The name "tuatara" derives from the Māori language, meaning "peaks on the back".[8] Tuataras feature in a number of indigenous legends, and are held as ariki (God forms). Tuataras are regarded as the messengers of Whiro, the god of death and disaster, and Māori women are forbidden to eat them.[15] The tuatara is featured on one side of the New Zealand 5 cent coin, to be phased out in October 2006 .

Sphenodon is derived from the Greek language for "wedge" (sphenos) and "tooth" (odon(t)); punctatus is Latin for "spotted"; guntheri alludes to Albert Günther, keeper of Zoology at the British Museum in London.

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Agamidae

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Red-headed Rock Agama

Agamids or lizards of the family Agamidae include more than 300 species in Africa, Asia, Australia, and a few in Southern Europe. Phylogenetically they may be sister to the Iguanidae, characterized by predominantly acrodont dentition. Agamids usually have well-developed, strong legs. Their tails cannot be shed and regenerated like those of Geckoes, though a certain amount of regeneration is observed in some. Many agamid species are capable of limited change of their colours. Ecologically they range from hot deserts to tropical rainforests.

Agamids

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Suborder:	Sauria
Family:	Agamidae

Subfamilies

Agaminae
Leiolepidinae
Draconinae

There have been very few studies of the Agamidae with the first comprehensive assessment by Moody (1980) followed by a more inclusive assessment by Frost and Etheridge (1989). Subsequent studies were based mitochondrial DNA loci with Macey et al. (2000) and Honda et al. (2000) and Joger (1991)(using allozymes) sampling across the Agamidae. Few other studies focused on clades within the family, but the Agamidae have not been as well investigated as the Iguanidae.

Among the Agamidae, six clades or lineages are generally recognized including the Leiolepidinae (Leiolepis), Uromasticinae (Uromastyx), Amphibolurinae (Australian and New Guinean), Hydrosaurinae (Hydrosaurus), Draconinae (South and Southeast Asian), and Agaminae (African and Arabian). The Chamaeleons of the sister family Chamaeleonidae are sometimes discussed as sub-family Chamaeleoninae and sub-family Agaminae (referring to Agamidae, not the Agaminae mentioned above).

Link

http://www.embl-heidelberg.de/~uetz/families/Agamidae.html

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Archosaurs

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herbivorous aetosaurs

crocodilians

Gharial

Archosaurs
Fossil range: Early Triassic - Recent

Living archosaurs include crocodiles (pictured above) and birds.

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Subclass:	Diapsida
Infraclass:	Archosauromorpha
(unranked)	Archosauria Cope, 1869

Groups

Crurotarsi
- Aetosauria
- Crocodilia (crocodiles)
- Phytosauria
- Rauisuchia
Ornithodira
- Pterosauria
- Marasuchus
- Dinosauria
  - Aves (birds)

Archosaurs (Greek for 'ruling lizards') are a group of diapsid reptiles that first evolved from Archosauriform ancestors during the Olenekian (Lower Triassic Period). They are represented today by birds and crocodiles. Archosaurs are set apart by having socketed teeth (a feature that inspired the traditional name, 'thecodonts', for the Triassic forms) and four-chambered hearts, among other characteristics. Most early forms were carnivores, with narrow serrated meat-tearing teeth. Their "reptilian" metabolism seem to have given them a clear advantage over the mammal-like therapsids that were their contemporaries in the arid interiors and strong monsoon climates that were the natural result of the single world-continent, Pangaea. Thus, whereas the Permian was dominated by synapsids, the Triassic came to be dominated by sauropsids.

There are two primary groups of archosaurs — the Ornithodira which were insignificant during the Middle Triassic but in the Late Triassic radiated as the dinosaurs and pterosaurs; and the Crurotarsi, which were the predominant group at this time, and included a number of purely Triassic groups like the rauisuchians, the phytosaurs, and the herbivorous aetosaurs, as well as the ancestors of the crocodilians.

A number of these archosaur groups - chiefly those large Crurotarsi that are in pre-cladistic books called the Thecodonts - became extinct 195 million years ago, during the Triassic-Jurassic extinction event. The survivors - the Dinosaurs and the Pterosaurs among the Ornithodira, and first the Sphenosuchia and Protosuchia then their descendants the Crocodilia among the Crurotarsi - flourished during the Jurassic and Cretaceous Periods. The dinosaurs dominated the land, the pterosaurs and later another archosaurian group, the birds, dominated the air,and the crocodiles dominated the rivers and swamps and even invaded the seas (the Teleosaurs and Metriorhynchidae).

Most of these taxa perished 65 million years ago, during the Cretaceous-Tertiary extinction event. The only groups of archosaurs to continue through to the Tertiary and, ultimately, to the present day, are the birds (which are descended from the dinosaurs) and the crocodylia (which include all modern crocodiles, alligators, and gharials).

Birds are traditionally treated as a separate class, Aves, while the rest of the archosaurs are treated as a subclass or infraclass, Archosauria, within the class Reptilia. More recently, with the cladistic method dominating Biology, only monophyletic groups are considered valid and birds are included within the division Archosauria.

Taxonomy

Infraclass Archosauromorpha
- (unranked) Archosauriformes
  - (unranked) ARCHOSAURIA
    - (unranked) Crurotarsi ("Pseudosuchia")
      - Order Phytosauria
      - Order Aetosauria
      - Order Rauisuchia
        Order Crocodilia
    - (unranked) Ornithodira ("Ornithosuchia" sensu Gauthier but without Ornithosuchidae)
      - Order Pterosauria
      - Superorder Dinosauria
        Class Aves

References

Benton, M. J. (2004), Vertebrate Paleontology, 3rd ed. Blackwell Science Ltd
Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, W. H. Freeman and Co. New York

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Crocodiles

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Superorder Crocodylomorpha

modern species

Eusuchia

Nile Crocodile

Crocodilia
Fossil range: Triassic - Recent
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Crocodilia, Owen, 1842
Suborders: Eusuchia, Protosuchia †, Mesosuchia †, Sebecosuchia †, Thalattosuchia †

Crocodilia is an order of large reptiles that appeared about 220 million years ago. They are the closest living relatives of birds, as the two groups are the only survivors of the Archosauria.[1]

Spelling

The group is often spelled 'Crocodylia' for consistency with the genus Crocodylus Laurenti, 1768. However, Richard Owen used the -i- spelling when he published the name in 1842, so by the usual rules of scientific classification his name has priority. In any case, the -i- spelling is a more accurate Latinization of the Greek κροκόδειλος (krokodeilos, literally "pebble-worm", referring to the shape and texture of the animal).

Evolution

When their extinct species and stem group are examined, crocodylians prove to have been a very diverse and adaptive group of reptiles. Not only are an ancient group of animals, at least as old as the dinosaurs, they also evolved into a great variety of forms. The earliest forms, the Sphenosuchians, evolved during the Late Triassic, and were highly gracile terrestrial forms built like greyhounds. Several terrestrial species during the Cretaceous evolved herbivory, such as Simosuchus clarki and Chimaerasuchus paradoxus. During the Jurassic and the Cretaceous marine forms in the family Metriorhynchidae such as Metriorhynchus evolved forelimbs that were paddle-like and had a tail similar to modern fish. Dakosaurus andiniensis a closely related species to Metriorhynchus had a skull that was adapted to eat large marine reptiles.

Eusuchia, a modern clade which includes the crown group Crocodylia, first appeared in the Lower Cretaceous of Europe. The recently-described fossil, Isisfordia duncani, lived approximately 95 to 98 million years ago, during the Cenomanian epoch of the Upper Cretaceous. Isisfordia is the second oldest known eusuchian, and the earliest crocodylian yet found in Australia. Eusuchians underwent a mass radiation during the Late Cretaceous and the Paleogene, in which they evolved into numerous forms, such as semi-aquatic dinosaur-eating species (Deinosuchus); hooved, terrestrial carnivores (Pristichampus), and 'hatchet'-shaped skulled forms (Baru).

In popular Culture

Several science fiction movies have giant crocodilians as their stars, such as Lake Placid, DinoCroc, and the crocodile series.

Extinct species

Superorder Crocodylomorpha
- (unranked) Sphenosuchia
  - Family Terrestrisuchidae
    Family Sphenosuchidae
- (unranked) Crocodyliformes
  - Family Shartegosuchidae
  - (unranked) Protosuchia
    - Family Protosuchidae
  - (unranked) Mesoeucrocodylia
    - Family Hsisosuchidae
      Family Gobiosuchidae
    - Suborder Thalattosuchia
      - Family Teleosauridae
        Family Metriorhynchidae
    - Suborder Metasuchia
      - (unranked) Notosuchia
        Family Notosuchidae
        Family Sebecosuchidae
        Family Baurusuchidae
      - (unranked) Neosuchia
        Family Trematochampsidae
        Family Peirosauridae
        Family Atoposauridae
        Family Dyrosauridae
        Family Pholidosauridae
        Family Goniopholididae
        
        Family Paralligatoridae
        (unranked) Eusuchia (see below)

Modern species

(unranked) Eusuchia
- Genus Hylaeochampsa (extinct)
- Genus Allodaposuchus (extinct)
  - Genus Borealosuchus (extinct)
    Genus Pristichampsus (extinct)
  - Superfamily Gavialoidea
    - Family Gavialidae
      - Genus Gavialis - Gharial/Gavial
        Genus Tomistoma - False Gharial/Gavial
  - Superfamily Crocodyloidea
    - Family Mekosuchidae (extinct)
    - Family Crocodylidae
      - Subfamily Crocodylinae - Crocodiles
  - Superfamily Alligatoroidea
    - Family Nettosuchidae (extinct)
    - Family Alligatoridae
      - Subfamily Alligatorinae - Alligators
      - Subfamily Caimaninae - Caimans

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Crocodilians description and comparison

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From the left: Heads of the Indian gharial (Gavialis gangeticus), American Alligator (Alligator mississippiensis), and an American Crocodile (Crocodylus acutus).

Like mammals and unlike most other reptiles (with the notable exception of monitor lizards), crocodiles have a four-chambered heart; however, unlike mammals, oxygenated and deoxygenated blood can be mixed when the foramen of Panazzi is open, which bridges both ventricles in the heart. The foramen is typically only open during diving, in order to shunt blood away from the lungs. Their blood has shown to have strong antibacterial properties.

All crocodilians have, like Homo sapiens (humans), thecodont dentition (teeth set in bony sockets) but unlike mammals, they replace their teeth throughout life (though not in 'extreme' old-age). Juvenile crocodilians replace teeth with larger ones at a rate as high as 1 new tooth per socket every month. After reaching adult size in a few years, however, tooth replacement rates can slow to two years and even longer. Very old members of some species have been seen in an almost "edentulous" (toothless) state, after teeth have been broken and replacement slowed or ceased. The result of this is that a single crocodile can go through at least 3,000 teeth in its lifetime. Each tooth is hollow, and the new one is growing inside the old. In this way, a new tooth is ready once the old is lost.

Crocodilians have a secondary bony palate that enables them to breathe when partially submerged, even if the mouth is full of water. Their internal nostrils open in the back of their throat, where a special part of the tongue called the "palatal valve" closes off their respiratory system when they are underwater. This way they can open their mouths underwater without choking. Most reptiles lack a secondary palate, but some skinks (family Scincidae) have evolved a bony secondary palate too, to varying degrees.

The tongue is attached to the floor of its mouth, making it hard to move at all.

They lack a vomeronasal organ (yet it is detectable in the embryo) and a urinary bladder.

They have alveoli in their lungs and a unique muscular attachment to the liver and viscera that acts as a piston to breathing, separating the thoracic and abdominal cavities (similar to the diaphragm of mammals). Although tegu lizards have a primitive proto-diaphragm, separating the pulmonary cavity from the visceral cavity and allowing greater lung inflation, this has a different evolutionary history.

Like all reptiles they have a relatively small brain, but it is more advanced than in other reptiles. Among other things it has a true cerebral cortex.

Crocodiles are often seen lying with their mouths open, a behavior called gaping. One of its functions is probably to cool them down, but since they also do this at night and when it is raining, it is possible that gaping has a social function too.

The crocodile basic body plan is a very successful one. Their form is well-adapted to their semi-aquatic niche, which is why modern forms look similar today as they did when the dinosaurs were still around (though only to the semi-aquatic forms). Mammals too have adapted to this body plan at least once in history. One ancestral whales family, Ambulocetidae, was an aquatic predator living in rivers and lakes. Ambulocetids filled an ecological niche similar to the modern crocodiles.

They have a semi-erect (semi-sprawled) posture, holding their legs more directly underneath them than most other reptiles (the chameleons are probably the only reptiles with a more erect posture than Crocodylia). This makes it possible for some species to even gallop on land if necessary; an Australian species can reach a speed of over 16 km/h while galloping on an irregular forest floor. But their ancestors actually had a fully erect posture; their sprawling and semi-erect posture are secondary and evolved after they adapted to a life in water as ambush predators. Their the ankle bones (tarsals) are highly modified. In other words, their locomotion is not primitive, it is in fact specialised to their semi-aquatic lifestyle. Their distant ancestors were fast-moving terrestrial predators, like Junggarsuchus sloani. An extinct terrestrial species, Pristichampsus rollinatii, even had hoof-like toes.

As in many other aquatic or amphibian tetrapods, the eyes, ears, and nostrils are all located on the same plane. They see well during the day and may even have colour vision, plus the eyes have a vertical, cat-like pupil which also gives them excellent night vision. The iris is silvery (light reflecting layer of tapetum behind the retina greatly increases their ability to see in weak light) also makes their eyes glow in the dark. A third transperant eyelid, the nictitating membrane, protects their eyes underwater. However, they cannot focus under water, meaning other senses are more important when submerged under water.

While birds and most reptiles have a ring of bones around each eye which supports the eyeball (the sclerotic ring), the crocodiles lack these bones, just like mammals and snakes. The eardrums are located behind the eyes and are covered by a movable flap of skin. This flap closes, along with the nostrils and eyes, when they dive, preventing water from entering their external head openings. The middle ear cavity has a complex of bony air-filled passages and a branching eustachian tube. There is also a small muscle (which is also seen in gecko) next to or upon the stapes, the stapedius, which probably functions in the same way as the mammalian stapedius muscle does, dampening strong vibrations.

The gender of the juvenile is determined by the incubation temperature. This means crocodilians do not have genetic sex determnination (like us), but a form of environmental sex determination which is based upon temperature embryo's undergo early in their development.

The skin is covered with non-overlapping scales composed of the protein keratin (the same protein that forms hoofs, skin, horns, feathers, hair, claws and nails in other tetrapods), which are shed individually. On the head the skin is actually fused to the bones of the skull. There are small plates of bone, called osteoderms or scutes, under the scales. Just like a tree, crocodile osteoderms have annual growth rings, and by counting them it is possible to tell their age. Osteoderms are found especially on the back, and in some species also on the belly. The overlapping rows of scutes cover the crocodile's body from head to tail, forming a tough protective armor. Beneath the scales and osteoderms is another layer of armor, both strong and flexible and built of rows of bony overlapping shingles called osteoscutes, which are embedded in the animal's back tissue. The blood-rich bumpy scales seen on their backs acts as solar panels.

Their spool-shaped vertebrae in their ancestors went from being biconcave to having a concave front and a convex back in the modern forms. This made the vertebral column more flexible and strong, a useful adaptation if you are hunting in water.

They possess ribs of dermal origin restricted to the sides of the ventral body wall. The collar bone (clavicle) is absent.

Crocodiles and gharials have modified salivary glands on their tongue (salt glands), which are used for excreting excess salt ions from their body. Alligators and caimans have them too, but here they are non-functioning. This indicates that at some point the common origin of the Crocodylia were adapted to saline/marine environments. This also explains their wide disribution across the continents (i.e. marine dispersal). Species like the saltwater crocodile (C. porosus) can survive protracted periods of time in the sea, and can hunt prey within this environment.

Crocodylians are known to swallow stones, gastroliths ("stomach-stones"), which act as a ballast in addition to aiding post-digestion processing of their prey. The crocodiylian stomach is divided into two chambers, the first one is described as being powerful and muscular, like a bird gizzard. This is where the gastroliths are found. The other stomach has the most acidic digestive system of any animal, and it can digest mostly everything from their prey; bones, feathers and horns.

The upper and lower jaws are covered with sensory pits, seen as small, black speckles on the skin, the crocodile version of the lateral organ we see in fish and many amphibians. But they have a completely different origin. These pigmented nodules encase bundles of nerve fibers that respond to the slightest disturbance in surface water, detecting vibrations and small pressure changes in water, making it possible for them to detect prey, danger and intruders even in total darkness. These sense organs are known as DPRs (Dermal Pressure Receptors). While alligators and caimans only have them on their jaws, crocodiles have similar organs on almost every scale on their body. The function of the DPRs on the jaws are clear, but it is still not quite clear what the organs on the rest of the body in crocodiles actually do. They are probably doing the same as the organs on their jaws, but it seems like they can do more than that, like assisting in chemical reception or even salinity detection.

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Avicephalans

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Coelurosauravus BW

Avicephala is an extinct order of bizarre diapsid reptiles that lived during the Late Permian and Triassic periods. Many species had odd specialized grasping limbs and prehensile tails, adapted to arboreal (and possibly aquatic) lifestyles.

Fossil range: Permian-Triassic
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Subclass: Diapsida
Avicephala, Senter, 2004
Families: Longisquamidae, Coelurosauravidae, Drepanosauridae

References

Colbert, E. H. & Olsen, P. E. (2001). "A new and unusual aquatic reptile from the Lockatong Formation of New Jersey (Late Triassic, Newark Supergroup)." American Museum Novitates: #3334, pp. 1-24.
Harris, J. D. & Downs, A. (2002). "A drepanosaurid pectoral girdle from the Ghost Ranch (Whitaker) Coelophysis quarry (Chinle Group, Rock Point Formation, Rhaetian), New Mexico." Journal of Vertebrate Paleontology: Vol. 22, #1, pp. 70-75.
Renesto, S. (1994). "Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of northern Italy." Journal of Vertebrate Paleontology: Vol. 14, #1, pp. 38-52.
Renesto, S. (2000): Bird-like head on a chameleon body: new specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of northern Italy. Rivista Italiana di Paleontologia e Stratigrafia 106: 157–180. HTML abstract
Senter, P. (2004). "Phylogeny of Drepanosauridae (Reptilia: Diapsida)." Journal of Systematic Palaeontology 2 (3): 257-268.

Anatomy and Lifestyle of the Avicephalans

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Rautiania

The name "avicephala" means "bird heads", in reference to the distinctive triangular skulls of these reptiles that mimic the shape of bird skulls. A few avicephalans, such as Hypuronector, even appear to have had pointed, toothless, bird-like beaks. This cranial similarity to birds has led a few scientists to theorize that birds descended from avicephalans like Longisquama, though a majority see the similarity simply as convergence. This similarity may also have led to the possible misidentification of the would-be "first bird", Protoavis (Renesto, 2000).

Avicephalans possessed a variety of odd and distinctive characteristics in addition to their bird-like skulls. Some displayed unique dermal appendages, such as the feather-like dorsal plumes of Longisquama, and the laterally-oriented rib-like rods of Coelurosauravus, which supported membranes and may have been used to glide from branch to branch in an arboreal habitat.

Another avicephalan group, the drepanosaurids, featured a suite of bizarre, almost chameleon-like skeletal features. Above the shoulders of most species was a specialized "hump" formed from fusion of the vertebrae, possibly used for advanced muscle attachments to the neck, and allowing for quick forward-striking movement of the head (perhaps to catch insects). Many had derived hands with two fingers opposed to the remaining three, an adaptation for grasping branches. Some individuals of Megalancosaurus (possibly exclusive to either males or females) had a primate-like opposable toe on each foot, perhaps used by one sex for extra grip during mating. Most species had broad, prehensile tails, sometimes tipped with a large "claw", again to aid in climbing. These tails, tall and flat like those of newts and crocodiles, have led some researches to conclude that they were aquatic rather than arboreal. Senter (2004) dismisses this idea, while Colbert and Olsen (2001), in their description of Hypuronector, state that while other drepanosaurs were probably arboreal, Hypuronector was uniquely adapted to aquatic life. The tail of this genus was extremely deep and non-prehensile – much more fin-like than other drepanosaurs.

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Fictional reptiles

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reptiles

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Fictional reptiles

Fictional dinosaurs

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Dinotopia LAFT cover

Literature

The dinosaurs from the book series Dinotopia
Michael Crichton's Jurassic Park series.

Film

26, a baby Chasmosaurus in Dinotopia series
Aladar and most other characters in Dinosaur
Godzilla
Half the characters in We're Back: A Dinosaur's Story
Littlefoot and most other characters in The Land Before Time
Tasha, extrasmart dinosaur in Land of the Lost series (1991)
Theodore Rex, a genetically modified Tyrannosaurus rex in Theodore Rex
Zippo, a neurotic Stenonychosaurus in Dinotopia series
Rhedosaurus the dinosaur from the Ray Haryhausen classic The Beast from 20,000 Fathoms
Yonggary from the movie 'Reptilian'

Animation, cartoon and puppetry

Barney, Baby Bop, and B.J. in Barney & Friends
The mousers... Little robot dinosaurs in the Teenage Mutant Ninja Turtles
Bob, Dawn, and Rex in Dilbert
Dink the Little Dinosaur
Steggy Doctari Thuggo Mr.Rex El Gordo in Thunderlizard Terrible in Eek! The Cat
Casimir and Hippolyte in the French series L'Île aux Enfants
Denver
Animated Godzilla (Zilla) (Not a true dinosaur but the son of a mutated iguana)
Dino in The Flintstones
Gertie the Dinosaur by Winsor McCay
"Grumpy" and many others from Land of the Lost
Half the characters from Harry and His Bucket Full of Dinosaurs
The characters from Dinosaurs
Most of the characters in Dinosaucers
Littlefoot and most other characters in The Land Before Time
Old Lace, a genetically engineered Deinonychus from the future in Marvel's Runaways
Rex the Green Dinosaur in Toy Story and Toy Story 2
Rocky B from the Brach's Rocks commercials
The three dinosaurs in Dinosaur Comics
Tootsie The Triceratops Pet Bubba caveduck Ducktales
T. Bone and most of his friends in the Extreme dinosaurs
Dorothy the Dinosaur, character in The Wiggles
Greymon, MetalGreymon, and numerous other Digimon
Various dinosaurs, including a Tyrannosaurus and a Stegosaurus, in the "Rite of Spring" sequence of Fantasia.
Dinosaur Transformers including Autobot Dinobots and Decepticon Trypticon.

Video games

Yoshi, and later on, Boshi, in the Mario series.
Birdo from the Mario series.
Rex, Dino Rhino, and various other enemies in the Mario series.
Blablanadon, a pterosaur in the Mario series.
Bub and Bob in Bubble Bobble
The Dinosaur Tribes in Star Fox Adventures
The Lizardmen in Spider-Man
Tirra in Bomberman/Bomberman Duel/Bomberman fantasy race
'Trinity', the name of a man-made dromaeosaurid from the video game 'Dino Stalker'.
Tricky the triceratops, from Diddy Kong Racing and the newer Star Fox games.
Rexaur a gigantic tyrannosaur enemy from Final Fantasy VIII
Many Pokémon are considered dinosaurs such as Lapras, Aerodactyl, Tyranitar, et cetera.

Lepidosaurs

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A Coachella Valley Fringe-toed Lizard

Lepidosaurians
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Subclass: Diapsida
Infraclass: Lepidosauromorpha
Superorder: Lepidosauria
Orders: Sphenodontia, Squamata

The Lepidosauria are reptiles with overlapping scales. They include the tuataras, lizards, snakes and amphisbaenians. Lepidosaurians are the most successful of modern reptiles.

Lepidosauria is a superorder of Sauropsida and comprises the orders :

Squamata - scaled reptiles (lizards, snakes and amphisbaenians)
Sphenodontia or Rhynchocephalia - tuatara

Links

This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Sauropterygia

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classification

scientific classification

Sauropterygians
Fossil range: Late Permian - Late Cretaceous

Artistic recreation of a plesiosaur

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Sauropterygia Owen, 1860

Orders

?Thalattosauriformes
Placodontia
Nothosauroidea
Plesiosauria

Sauropterygia ("lizard flippers") is a group of very successful aquatic reptiles that flourished during the Age of the Dinosaurs before they became extinct. They are united by a radical adaptation of their shoulder, designed to support powerful flipper strokes. Some later sauropterygians like the pliosaurs developed a similar mechanism in their pelvis.

The earliest sauropterygians appeared about 245 million years ago (Ma), at the start of the Triassic period. Early examples were small (around 60 cm), semi-aquatic lizard-like animals with long limbs (pachypleurosaurs), but they quickly grew to be several meters long and spread into shallow waters (nothosaurs). The Triassic-Jurassic extinction event wiped them all out except for the plesiosaurs. During the Early Jurassic these diversified quickly into both long-necked small-headed plesiosaurs proper, and short-necked large-headed pliosaurs. Originally it was thought that Plesiosaurs and Pliosaurs were two distinct superfamilies that followed separate evolutionary paths. It now seems that these were simply morphotypes in that both types evolved a number of times, with some pliosaurs evolving from plesiosaur ancestors, and vice-versa.

Each morphotype filled a specific ecological role. The large pliosaurs, like the Jurassic Rhomaleosaurus, Liopleurodon and Pliosaurus, and the Cretaceous Kronosaurus and Brachauchenius, were the superpredators of the Mesozoic seas, around 7 to 12 meters in length, and filled a similar ecological role to that of killer whales today. The long-necked plesiosaurs, meanwhile, included both those with medium-long necks, like the 3 to 5 meter-long Plesiosauridae and the Cryptoclididae, and the Jurassic and Cretaceous Elasmosauridae, which evolved progressively longer and more flexible necks, so that by the middle and late Cretaceous the entire animal was over 13 meters in length (e.g. Elasmosaurus), although as most of this was the neck, the actual body size was much smaller than that of the larger pliosaurs. These long-necked forms undoubtedly fed on fish, which they probably snared in their tooth-lined jaws with rapid lunges of the neck and head.

Disregarding reports of lake monsters like the Loch Ness Monster, they all perished 65 Mya during the Cretaceous-Tertiary extinction event.

Classification is difficult because the demands of the aquatic environment caused the same characteristics to evolve multiple times, illustrating convergent evolution. While sauropterygians are considered diapsids, they are also sometimes classified with turtles. The bulky-bodied, mollusc-eating placodonts may also be sauropterygians. In addition to the modifications of the shoulder, the group is also united by several modifications in their skulls.

Taxonomy

Class Sauropsida (reptiles)
- Infraclass Lepidosauromorpha (lizards and relatives)
  - SUPERORDER SAUROPTERYGIA
    - Order Thalattosauriformes
      - Suborder Thalattosauria
    - Order Placodontia
    - (unranked) Eusauropterygia
      - Order Nothosauroidea
        Suborder Pachypleurosauria
        
        Suborder Nothosauria
      - (unranked) Pistosauroidea
        Corosaurus
        Chinchenia
        Kwangsisaurus
        Cymatosaurus
        Family Pistosauridae
        
        Order Plesiosauria
        Suborder Plesiosauroidea (long-necked plesiosaurs)
        Suborder Pliosauroidea (short-necked plesiosaurs)

Nothosaurs

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Nothosaurs

Fossil range: Triassic

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Sauropterygia
Order:	Nothosauria Baur, 1889

Suborders

Suborder Pachypleurosauria
- Pachypleurosauridae
Suborder Nothosauria
- Simosauridae
  Germanosauridae
  Nothosauridae

Nothosaurs (order Nothosauria) were Triassic marine sauropterygian reptiles that may have lived like seals of today, catching food in water but coming ashore on rocks and beaches. They averaged about three meters in length, with a long body and tail. The feet had become paddle-like, and were most certainly webbed in life, to help power the animal when swimming. The neck was quite long, and the head was elongate and flattened, and relatively small in relation to the body. The margins of the long jaws were equipped with numerous sharp outward-pointing teeth, indicating a diet of fish.

The nothosaurs consist of two suborders--the Pachypleurosaurs, tiny, primitive forms, and the true Nothosaurs, which evolved from pachypleurosaurs. Nothosaur-like reptiles were in turn ancestral to the more completely marine plesiosaurs, which replaced them at the end of the Triassic period.

References

Fantastic Facts About Dinosaurs (ISBN 0-75253-166-2)
Benton, M. J. (2004), Vertebrate Paleontology, 3rd ed. Blackwell Science Ltd classification
Colbert, E. H., (1969), Evolution of the Vertebrates, John Wiley & Sons Inc (2nd ed.)
Rieppel, O., (2000), Sauropterygia I, placodontia, pachypleurosauria, nothosauroidea, pistosauroidea: In: Handbuch der Palaoherpetologie, part 12A, 134pp. Verlag Dr. Friedrich Pfeil Table of contents

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Pachypleurosaur

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pachypleurosaurs

reptiles

Triassic period

Pachypleurosaurs

Fossil range: Triassic

Keichousaurus

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Sauropterygia
Order:	Nothosauroidea
Suborder:	Pachypleurosauria Nopcsa, 1928
Family:	Pachypleurosauridae Nopcsa, 1928

Genera

Anarosaurus
Dactylosaurus
Hanosaurus
Keichousaurus
Neusticosaurus
Serpianosaurus

Pachypleurosaurs were primitive Triassic sauropterygian reptiles that vaguely resembled aquatic lizards, and are limited to the Triassic period. They were elongate animals, ranging in size from 20 cm to about a meter in length, with small heads, long necks, paddle-like limbs, and long deep tails. The limb girdles are greatly reduced, so it is unlikely these animals could move about on land. The widely spaced peg-like teeth project at the front of the jaws, and indicate that these animals fed on fish.

Pachypleurosaurs were originally and are often still included among the Nothosaurs (Carroll 1988, Benton 2004). In some cladistic classifications however (Rieppel 2000), they are considered the sister group to the Eusauropterygia, the clade that includes the nothosaurs and plesiosaurs.

References

Benton, M. J. (2004), Vertebrate Paleontology, 3rd ed. Blackwell Science Ltd classification
Carroll, R.L. (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co.
Rieppel, O., (2000), Sauropterygia I, placodontia, pachypleurosauria, nothosauroidea, pistosauroidea: In: Handbuch der Palaoherpetologie, part 12A, 134pp. Verlag Dr. Friedrich Pfeil Table of contents

External links

Lepidosauromorpha: Pachypleurosauridae - Palaeos

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Squamata

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Scientific classification
Kingdom: Animalia
Phylum: Chordata

Class: Sauropsida
Order: Squamata, Oppel, 1811

Suborders
Lacertilia- Lizards
Serpentes - Snakes
Amphisbaenia - Worm lizards

Squamata (scaled reptiles) is the largest recent order of reptiles, including lizards and snakes. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the braincase. This is particularly visible in snakes, which are able to detach their jaws entirely to accommodate very large penises. The male members of the group Squamata are the only vertebrates with a hemipenis. This is also the only reptile group where we can find both viviparous and ovoviviparous species, as well as the usual oviparous reptiles.

Classically, the order is divided into three suborders:

Lacertilia, the lizards;
Serpentes, the snakes;
Amphisbaenia, the worm lizards.

Of these, the lizards form a paraphyletic group. In newer classifications the name Sauria is used for reptiles and birds in general, and the Squamata are divided differently:

Suborder Iguania (the iguanas and chameleons)
Suborder Scleroglossa
- Infraorder Gekkota (the geckos)
  Infraorder Anguimorpha (the monitors, goannas, Komodo dragon, Gila monster, and slow-worms)
  Infraorder Scincomorpha (skinks and common European lizards)
  Infraorder Serpentes (the snakes)
  Infraorder Amphisbaenia

The exact relationships within these two suborders are not entirely certain yet, though recent research strongly suggests that several families form a venom clade which encompasses a majority (nearly 60%) of Squamate species.

The Squamata do not include the tuataras, New Zealand reptiles resembling lizards.

Lizards

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Haeckel Lacertilia "Lacertilla", from Ernst Haeckel's Artforms of Nature, 1904

Fossil range: Jurassic - Recent
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Squamata
Suborder: Lacertilia, Günther, 1867

Lizards are reptiles of the order Squamata, which they share with the snakes (Ophidians). They are usually four-legged, with external ear openings and movable eyelids. Species range in adult length from a few centimeters (some Caribbean geckos) to nearly three meters (Komodo dragons).

Some lizard species called "glass snakes" or "glass lizards" have no functional legs, though there are some vestigial skeletal leg structures. They are distinguished from true snakes by the presence of eyelids and ears. The tail of glass lizards, like many other lizards, will break off as a defense mechanism, unlike snakes.

Many lizards can change color in response to their environments or in times of stress. The most familiar example is the chameleon, but more subtle color changes occur in other lizard species as well (most notably the anole, also known as the "house chameleon" or "chamele").

Lizards typically feed on insects or rodents. A few species are omnivorous or herbivorous; a familiar example of the latter is the iguana, which is unable to properly digest animal protein. Until very recently, it was thought that only two lizard species were venomous: the Mexican beaded lizard and the closely-related Gila monster, both of which live in northern Mexico and the southwest United States. However recent research at the University of Melbourne, Australia and Pennsylvania State University has revealed that in fact many lizards in the iguanians and monitor (lizard) families have venom-producing glands. None of these poses much danger to humans, as their poison is introduced slowly by chewing, rather than injected as with poisonous snakes. Nine toxins previously thought to only occur in snakes have been discovered, and a number of previously unseen chemicals as well.

These revelations are prompting calls for a complete overhaul of the classification system for lizard species to form a venom clade. "These papers threaten to radically change our concepts of lizard and snake evolution, and particularly of venom evolution," says Harry Greene, a herpetologist at Cornell University in New York.

Most other lizard species are harmless to humans (most species native to North America, for example, are incapable even of drawing blood with their bites). Only the very largest lizard species pose threat of death; the Komodo dragon, for example, has been known to attack and kill humans and their livestock. The Gila Monster and Beaded Lizard are venomous however, and though not deadly, can inflict extremely painful and powerful bites. The chief impact of lizards on humans is positive; they are significant predators of pest species; numerous species are prominent in the pet trade; some are eaten as food (for example, iguanas in Central America); and lizard symbology plays important, though rarely predominant roles in some cultures (e.g. Tarrotarro in Australian mythology).

Most lizards lay eggs, though a few species are capable of live birth. Many are also capable of regeneration of lost limbs or tails.

Lizards in the Scincomorpha family, which include skinks (such as the blue-tailed skink), often have shiny, iridescent scales that appear moist. However, like all other lizards, they are dry-skinned and generally prefer to avoid water. All lizards are able to swim if needed, however, and a few (such as the Nile monitor) are quite comfortable in aquatic environments.

Lizards as pets

Many species of lizard are now sold as pet species. A few of these include iguanas, bearded dragon, leopard geckos, tegus, and monitor lizards to name a few. In general, lizards require more maintenance than other exotic pets, particularly snakes and tarantulas. Their feces are usually more offensive, requiring frequent cage cleanings.

References

Anthony Herrel's lizard page
The EMBL reptile database
Tiny gecko - the 'world's smallest' lizard
Venom found to be widespread in lizards [1]

This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Classification of lizards

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Suborder Lacertilia (Sauria) - (Lizards)

†Family Bavarisauridae
†Family Eichstaettisauridae
Infraorder Iguania
- †Family Arretosauridae
  †Family Euposauridae
  Family Corytophanidae (casquehead lizards)
  Family Iguanidae (iguanas and spinytail iguanas)
  Family Phrynosomatidae (earless, spiny, tree, side-blotched and horned lizards)
- Family Polychrotidae (anoles)
  - Family Leiosauridae (see Polychrotinae)
- Family Tropiduridae (neotropical ground lizards)
  - Family Liolaemidae (see Tropidurinae)
    Family Leiocephalidae (see Tropidurinae)
- Family Crotaphytidae (collared and leopard lizards)
  Family Opluridae (Madagascar iguanids)
  Family Hoplocercidae (wood lizards, clubtails)
  †Family Priscagamidae
  †Family Isodontosauridae
  Family Agamidae (agamas)
  Family Chamaeleonidae (chameleons)
Infraorder Gekkota
- Family Gekkonidae (geckos)
  Family Pygopodidae (legless lizards)
  Family Dibamidae (blind lizards)
Infraorder Scincomorpha
- †Family Paramacellodidae
  †Family Slavoiidae
  Family Scincidae (skinks)
  Family Cordylidae (spinytail lizards)
  Family Gerrhosauridae (plated lizards)
  Family Xantusiidae (night lizards)
  Family Lacertidae (wall lizards or true lizards)
  †Family Mongolochamopidae
  †Family Adamisauridae
  Family Teiidae (tegus and whiptails)
  Family Gymnophthalmidae (spectacled lizards)
Infraorder Diploglossa
- Family Anguidae (glass lizards)
  Family Anniellidae (American legless lizards)
  Family Xenosauridae (knob-scaled lizards)
Infraorder Platynota (Varanoidea)
- Family Varanidae (monitor lizards)
  Family Lanthanotidae (earless monitor lizards)
  Family Helodermatidae (gila monsters)
  †Family Mosasauridae (marine lizards)

Extant Lacertilia families

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This is a list of the extant Lacertilia families. Larcertilia is the suborder of reptiles commonly known as lizards.

Taxonomy

There are five infraorders which separate the lizards, these are: Diploglossa, Gekkota, Iguania, Platynota and Scincomorpha. This separation is based mainly on morphological similarities between family groups.

The Diploglossans and Platynotans are two closely related infraorders which are have very diverse families. Very few generalisations can be placed upon these families morphologically. Many species are limbless, while others have fully formed limbs. It is believed that these lizards are the closest lizard relation to the snakes.

The Gekkotans are the second most diverse group of lizards. They can be morphologically distinguished by the absence of temporal arches, which allows greater moveability of the head. Most species also have cloacal sacs and fixed eyelids.

The Iguanians are another diverse group of lizards. All iguanians are fully limbed. Most species ambush their prey, capture it with their tongue and have skin modification, such as crests and fans, used for many different reasons.

The Scincomorphans are the most diverse group of lizards, accounting for almost half the speices of lizards. The major distinguishing morphological feature of the Scincomorphs, is the presence of unsocketed teeth on the inner face of the jaw bones. They also lack the skin modifications present in many of the iguanians. This family contains varying degrees of limb reduction, from completely formed limbs to completely absent of limbs.

As with most taxonomic classifications, there are many different interpretations of the evolutionary relationships. These include moving of familes to different infraorders, merging or splitting of the infraorders and merging and splitting of the families.

Family	Common Names	Example Species
Diploglossa
Anguidae Oppel, 1811	Glass lizards	Slow Worm (Anguis fragilis)
Anniellidae Gray, 1852	American legless lizards	California Legless Lizard (Anniella pulchra)
Xenosauridae Cope, 1866	Knob-scaled lizards	Chinese Crocodile Lizard (Shinisaurus crocodilurus)
Gekkota
Family	Common Names	Example Species
Dibamidae Boulenger, 1884	Blind lizards	Dibamus nicobaricum
Gekkonidae Gray, 1825	Geckos	Thick-tailed Gecko (Underwoodisaurus milii)
Pygopodidae Boulenger, 1884	Legless lizards	Burton's Snake Lizard (Lialis burtonis)
Iguania
Family	Common Names	Example Species
Agamidae Spix, 1825	Agamas	Eastern Bearded Dragon (Pogona barbata)
Chamaeleonidae Gray, 1825	Chameleons	Veiled Chameleon (Chamaeleo calyptratus)
Corytophanidae Frost & Etheridge, 1989	Casquehead lizards	Plumed Basilisk (Basiliscus plumifrons)
Crotaphytidae Frost & Etheridge, 1989	Collared and leopard lizards	Common Collared Lizard (Crotaphytus collaris)
Hoplocercidae Frost & Etheridge, 1989	Wood lizards or clubtails	Club-tail Iguana (Hoplocercus spinosus)
Iguanidae	Iguanas	Marine Iguana (Amblyrhynchus cristatus)
Leiosauridae Frost et al., 2001	-	Darwin's Iguana (Diplolaemus darwinii)
Opluridae Frost & Etheridge, 1989	Madagascan iguanas	Chalarodon (Chalarodon madagascariensis)
Phrynosomatidae Frost & Etheridge, 1989	Earless, spiny, tree, side-blotched and horned lizards	Greater Earless Lizard (Cophosaurus texanus)
Polychrotidae Frost & Etheridge, 1989	Anoles	Caronlina Anole (Anolis carolinensis)
Tropiduridae Frost & Etheridge, 1989	Neotropical ground lizards	(Microlophus peruvianus)
Platynota
Family	Common Names	Example Species
Helodermatidae	Gila monsters	Gila Monster (Heloderma suspectum)
Lanthanotidae	Earless Monitor	Earless Monitor (Lanthanotus borneensis)
Varanidae	Monitors lizards	Perentie (Varanus giganteus)
Scincomorpha
Family	Common Names	Example Species
Cordylidae	Spinytail lizards	Girdle-tailed Lizard (Cordylus warreni)
Gerrhosauridae	Plated lizards	Sudan Plated Lizard (Gerrhosaurus major)
Gymnophthalmidae	Spectacled lizards	-
Lacertidae Oppel, 1811	Wall or true lizards	Eyed Lizard (Lacerta lepida)
Scincidae Oppel, 1811	Skinks	Western Blue-tongued Skink (Tiliqua occipitalis)
Teiidae	Tegus or whiptails	Blue Tegu (Tupinambis teguixin)
Xantusiidae	Night lizards	Granite Night Lizard (Xantusia henshawi)

References

Cogger, H.G., R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press. ISBN 1-877019-69-0.
Tropiduridae. Retrieved on 2006-05-30.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Iguanas

Attachment	Size
Green iguana (Iguana iguana)	125.14 KB

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iguanas

classification

Iguanas

http://www.sfetcu.com/sites/default/files/63_Building_guana.jpg

Green iguana (Iguana iguana)

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Order:	Squamata
Suborder:	Sauria
Family:	Iguanidae

Genera

Amblyrhynchus
Brachylophus
Conolophus
Ctenosaura
Cyclura
Dipsosaurus
Iguana
Sauromalus

Frost et al. (1989) redefined this family. The genera belonging to the different subfamilies were assigned to separate families. This view is not generally accepted.

Frost et al classification of iguanas

Family Iguanidae

Genus Amblyrhynchus
Genus Brachylophus
Genus Conolophus
Genus Ctenosaura
Genus Cyclura
Genus Dipsosaurus
Genus Iguana
Genus Sauromalus
Genus Armandisaurus (extinct)
Genus Lapitiguana (extinct)
Genus Pumila (extinct)

Traditional classification

Family Iguanidae

Subfamily Corytophaninae: casquehead lizards
Subfamily Crotaphytinae: collared and leopard lizards
Subfamily Hoplocercinae: wood lizards, clubtails
Subfamily Iguaninae: iguanas and spinytail iguanas
Subfamily Leiocephalinae
Subfamily Leiosaurinae
Subfamily Liolaeminae
Subfamily Oplurinae: Madagascar iguanids
Subfamily Phrynosomatinae: earless, spiny, tree, side-blotched and horned lizards
Subfamily Polychrotinae: anoles
Subfamily Tropidurinae: neotropical ground lizards

References

Frost, D.E. and R.E. Etheridge (1989) A Phylogenetic Analysis and Taxonomy of Iguanian Lizards (Reptilia: Squamata). Univ. Kansas Mus. Nat. Hist. Misc. Publ. 81
Frost, D.R., R. Etheridge, D. Janies and T.A. Titus (2001) Total evidence, sequence alignment, evolution of Polychrotid lizards, and a reclassification of the Iguania (Squamata: Iguania). American Museum Novitates 3343: 38 pp.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Snakes

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Snakes
Fossil range: Cretaceous - Recent

A coral snake

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Order:	Squamata
Suborder:	Serpentes Linnaeus, 1758

Superfamilies and Families

Henophidia

Aniliidae
Anomochilidae
Boidae
Bolyeriidae
Cylindrophiidae
Loxocemidae
Pythonidae
Tropidophiidae
Uropeltidae
Xenopeltidae

Typhlopoidea

Anomalepididae
Leptotyphlopidae
Typhlopidae

Xenophidia

Acrochordidae
Atractaspididae
Colubridae
Elapidae
Hydrophiidae
Viperidae

Snakes (from Old English snaca, and ultimately from the Proto-Indo-European base *snag- or *sneg-, "to crawl"), also known as ophidians, are cold-blooded legless reptiles closely related to lizards, which share the order Squamata. There are also several species of legless lizard which superficially resemble snakes, but are not otherwise related to them. A love of snakes is called ophiophilia, a fear of snakes is called ophidiophobia. A specialist in snakes is an ophiologist.

An old synonym for snake is serpent (which comes from Old French, and ultimately from *serp-, "to creep"[1]); in modern usage this usually refers to a mythic or symbolic snake, and information about such creatures can be found under serpent (symbolism). This article deals with the biology of snakes.

References

Romulus Whitaker (English edition); Tamil translation by O.Henry Francis (1996). நம்மை சுட்ரியுள்ள பாம்புகள் (Snakes around us, Tamil). National Book Trust. ISBN 81-237-1905-1.

Vipers

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Viperidae

Asp viper, Vipera aspis

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Reptilia
Order:	Squamata
Suborder:	Serpentes
Family:	Viperidae Oppel, 1811

Synonyms

Viperae - Laurenti, 1768
Viperini - Oppel, 1811
Viperidae - Gray, 1825^[1]

The Viperidae are a family of venomous snakes commonly referred to as vipers, although the term viperids is more specific and distinguishes them from the viperines (subfamily Viperinae). These snakes are found all over the world, except in Australia and Madagascar. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four subfamilies are currently recognized.^[2]

Description

All viperids have a pair of relatively long, solenoglyphous (hollow) fangs, that are used to inject venom from glands located towards the rear of the upper jaws. Each of the two fangs is located at the front of the mouth on a short maxillary bone that can rotate back and forth. When not in use, the fangs fold back against the roof of the mouth and are enclosed in a membranous sheath. The left and right fangs can be rotated together or independently. During a strike, the mouth can open nearly 180 degrees and the maxilla rotates forward, erecting the fang. The jaws close on impact and powerful muscles that surround the venom glands contract to inject the venom as the fangs penetrate. This action is lightning-fast and is more a stab than a bite. Viperids use this mechanism both to immobilize their prey and in self-defense.

Almost all vipers have keeled scales, a stocky build with a short tail and, due to the location of the venom glands, a triangular-shaped head distinct from the neck. Their eyes have vertically elliptical, or slit-shaped, pupils that can open wide to cover most of the eye or close almost completely, which helps them to see in a wide range of light levels. Typically, vipers are nocturnal, ambush predators.

Compared to many other snakes, vipers often appear rather sluggish. Most are ovoviviparous, giving birth to live young, but a few lay eggs. Indeed, the name of this group is derived from Latin (vivo = live, parthus = birth) and is in reference to the more common of these two reproductive modes.^[3]

Venom

As opposed to the elapids, which produce mainly neurotoxic venom, viperid venoms are largely proteolytic, meaning that they rapidly destroy blood and tissue. This kind of venom is also dual-purpose. Most vipers have poor digestive systems and often rely on their venom not just to immobilize their prey, but also to aid in the digestion thereof: fluids in the stomach digest the meal from the outside in, while the venom digests it from the inside out.

There are, of course, always exceptions and a number of viperid species produce venom that is partially or even entirely neurotoxic, which can make them extremely dangerous. Examples are the tropical rattlesnakes (Crotalus durissus), some Mojave rattlesnakes (Crotalus scutulatus), and the rare mountain adder (Bitis atropos).

Due to the nature of proteolytic venom, a viperid bite is often a very painful experience and should always be taken seriously, even though it is not necessarily fatal. Even with prompt and proper treatment, a bite can still result in a permanent scar, and in the worst cases the affected limb may even have to be amputated. A victim's actual fate is impossible to predict as this depends on many factors, including (but not limited to) the species and size of the snake involved, how much venom was injected (if any) and the size and condition of the patient prior to being bitten. The patient may also be allergic to the venom and/or the antivenin.

Subfamilies

Subfamily^[2]	Authority^[2]	Genera^[2]	Species^[2]	Common name	Geographic range^[1]
Azemiopinae	Liem, Marx & Rabb, 1971	1	1	Fea's viper	Myanmar, southeastern Tibet across southern China (Fujien,Guangxi,Jiangxi,Kweichow,Sichuan,Yunnan,Zhejiang) to northern Vietnam.
Causinae	Cope, 1859	1	6	Night adders	Subsaharan Africa
Crotalinae	Oppel, 1811	18	151	Pit vipers	In the Old World from eastern Europe eastward through Asia to Japan, Taiwan, Indonesia, peninsular India and Sri Lanka. In the New World from southern Canada southward through Mexico and Central America to southern South America.
Viperinae	Oppel, 1811	12	66	True or pitless vipers	Europe, Asia and Africa.

Type genus = Vipera - Laurenti, 1768^[1]

Taxonomy

That Viperidae is attributed to Oppel (1811), as opposed to Laurenti (1768) or Gray (1825), is subject to some interpretation. However, the consensus among leading experts is that Laurenti used viperae as the plural form of vipera (Latin for viper, adder or snake) and did not intend for it to indicate a a family group taxon. Rather, it is attributed to Oppel, based on his Viperini as a distinct family group name, despite the fact that Gray was the first to use the form Viperinae.^[1]

Cited references

^ ^a ^b ^c ^d McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. ISBN 1-893777-00-6 (series). ISBN 1-893777-01-4 (volume).
^ ^a ^b ^c ^d ^e Viperidae (TSN 174294). Integrated Taxonomic Information System. Accessed on 10 August 2006.
^ Schuett GW, Höggren M, Douglas ME, Greene HW. 2002. Biology of the Vipers. Eagle Mountain Publishing, LC. 580 pp. 16 plates. ISBN 0-9720154-0-X.

Marine reptiles

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Sea turtle

Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semi-aquatic life in a marine environment.

The earliest marine reptiles arose in the Permian period during the Paleozoic era. During the Mesozoic era, many groups of reptiles became adapted to life in the seas, including such familiar clades as the ichthyosaurs, plesiosaurs, placodonts, and mosasaurs.

After the first mass extinction at the end of the Cretaceous period, marine reptiles were less numerous. Extant marine reptiles include marine iguanas, sea snakes, sea turtles, and some species of crocodiles.

Some marine reptiles, such as ichthyosaurs and mosasaurs, rarely venture onto land and give birth in the water. Others, such as sea turtles and saltwater crocodiles, still return to shore to lay their eggs.

Euryapsids

Plesiosaurs
Ichthyosaurs
placodonts

Diapsids

mosasaurs
saltwater crocodiles
marine Iguanas

This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Video: Manado Marine Reptiles

Sea turtles

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species

scientific classification

Green SeaTurtle Hawaiian Green Sea Turtle

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Testudines
Suborder: Cryptodira
Superfamily: Chelonioidea, Bauer, 1893

Genera

Family Cheloniidae (Oppel, 1811)
- Caretta
- Lepidochelys
- Chelonia
- Eretmochelys
- Natator
Family Dermochelyidae
Family Protostegidae (extinct)
Family Toxochelyidae (extinct)
Family Thalassemyidae (extinct)

Sea turtles (Chelonioidea) are turtles found in all the world's oceans with the exception of the Arctic Ocean, and some species travel between oceans. The Flatback turtle is found solely on the northern coast of Australia. The Leatherback Sea Turtle is the largest, measuring six or seven feet (2 m) in length at maturity, and three to five feet (1 to 1.5 m) in width, weighing up to 1300 pounds (600 kg). Most other species are smaller, being two to four feet in length (0.5 to 1 m) and proportionally less wide. There are seven types of sea turtles: Kemp's Ridley, Flatback, Green, Olive Ridley, Leatherback, Loggerhead, and Hawksbill.

Different species are distinguished by varying anatomical aspects: for instance the prefrontal scales on the head, the number of and shape of scutes on the carapace, and the type of inframarginal scutes on the plastron. The Leatherback is the only sea turtle that does not have a hard shell, instead carrying a mosaic of bony plates beneath its leathery skin.

Sea turtles have an extraordinary sense of time and location. They are highly sensitive to the Earth's magnetic field and probably use it to navigate. They can live up to 189 years. The fact that most species return to nest at the locations where they were born seems to indicate an imprint of that location's magnetic features. The ridley turtles are especially peculiar because instead of nesting individually like the other species, they come ashore in one mass arrival known as an "arribada" (arrival). With the Kemp's ridley this occurs during the day and on only one beach in the entire world. Their numbers used to range in the thousands but due to the effects of extensive egg poaching and hunting in previous years the numbers are now in the hundreds.

After about 30 years of maturing, adult female sea turtles return to the land to nest, usually on the same beach from which they hatched. This can take place every two to four years in maturity. They make from four to seven nests per nesting season. They dig a hole with their hind flippers and lay from 70 to 190 eggs in it (depending on the species) before covering it up and returning to the ocean. Some of the eggs are unfertilized 'dummy eggs' and the rest contain young turtles. Incubation takes about 2 months. When the eggs hatch, these baby turtles dig their way out and seek the ocean. Only a very small proportion of them (usually 1%) will be successful, as many predators wait to eat the steady stream of new hatched turtles (since many sea turtles lay eggs en masse, the eggs also hatch en masse).

Parareptiles

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Nyctiphruretus

Parareptilia
Fossil range: Permian to Triassic (without Chelonia); or Permian to Recent (if incl. Chelonia)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Superclass: Tetrapoda
Class: Reptilia/Sauropsida
Subclass: Parareptilia, Olson, 1947

Parareptilia ("at the side of reptiles") is a subclass or clade of Reptiles which are variously defined as an extinct group of primitive anapsids, or a more cladistically correct alternative to Anapsida. Whether the term is valid depends a lot on the phylogenetic position of turtles, the relationships of which to other reptilian groups are still uncertain

The name Parareptilia was coined by Olson 1947 to refer to an extinct group of Paleozoic reptiles, as opposed to the rest of the reptiles or Eureptilia ("true reptiles".

The name fell into disuse, until it was revived by cladistic studies, to refer to anapsida that were thought unrelated to turtles. Gauthier et al. 1988 provided the first phylogenetic definitions for the names of many amniote taxa, including Sauropsida as the parent clade for Reptilia, and argued cladistically that captorhinids and turtles were sister groups, constituting the clade Anapsida (in a much more limited context than the definition given by Romer 1967). A name had to be found for various Permian and Triassic reptiles no longer included in the Anapsids, and "Parareptiles" was chosen. However, they did not feel confident enough to erect Parareptilia as a formal taxon. Their cladogram was as follows:

--o AMNIOTA
  |-- Synapsida
  `--o Sauropsida
     |--o "parareptiles"
     |  |-- Mesosauridae
     |  `--+-- Procolophonidae
     |      `--+-- Millerettidae
     |          `-- Pareiasauria
     `--o Reptilia
        |---o Anapsida
        |   |-- Captorhinidae
        |   `-- Testudines
        `--o Romeriida
           |-- Protorothyrididae
           `-- Diapsida

Laurin and Reisz 1995 presented a different cladogram, in which the Reptilia are divided into Parareptilia (now a formal taxon) and Eureptilia. The Captorhinidae are transferred to the Eureptilia, and the Parareptilia includes both early Anapsid reptiles and turtles, but not the Captorhinidae and Protorothyrididae. The mesosaurs are placed outside both groups, as the sister taxon to the reptiles (but still sauropsids). The traditional taxon of Anapsida is rejected as paraphyletic. This gives the following:

--o AMNIOTA
  |-- Synapsida
  `--o Sauropsida
     |-- Mesosauridae
     `--o Reptilia
        |--o Parareptilia
        |  |-- Millerettidae
        |  `--+-- Pareiasauria
        |      `--+-- Procolophonidae
        |          `-- Testudines
        `--o Eureptilia
           |-- Captorhinidae
           `--o Romeriida
              |-- Protorothyrididae
              `-- Diapsida

In contrast, Rieppel, 1994, 1995; Rieppel & deBraga, 1996; and deBraga & Rieppel, 1997 have argued that turtles are actually related tro sauropterygia, and hence are diapsids. The diapsid affinities of turtles have also been supported by molecular phylogeny (e.g. Zardoya and Meyer 1998). If so, this would mean that the Parareptilia would become a wholy extinct clade. However this hypothesis is not very widely accepted among vertebrate paleontologists, and Benton 2000, 2004, retains the traditional class Anapsida for the "parareptiles" and turtles.

References

Benton, M. J., Vertebrate Paleontology, 2nd ed. 2000, 3rd ed. 2004, Blackwell Science Ltd,
deBraga M. & Rieppel, O., 1997. Reptile phylogeny and the interrelationships of turtles. Zoological Journal of the Linnean Society 120: 281-354.
deBraga, M. & Reisz, R. R., 1996: The Early Permian reptile Acleistorhinus pteroticus and its phylogenetic position. Journal of Vertebrate Paleontology: Vol. 16, #3, pp. 384-395
Gauthier, J., A. G. Kluge, & T. Rowe. 1988. The early evolution of the Amniota. In M. J. Benton (ed.) The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds: 103-155. Oxford: Clarendon Press.
Laurin, M., & Gauthier, J. A., 1996 Phylogeny and Classification of Amniotes, at the Tree of Life Web Project
Laurin, M. & R. R. Reisz. 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society 113: 165-223. (abstract)
Olson E. C. 1947. The family Diadectidae and its bearing on the classification of reptiles. Fieldiana Geology 11: 1-53.
Rieppel, O. 1994. Osteology of Simosaurus gaillardoti and the relationships of stem-group sauropterygia. Fieldiana Geology 1462: 1-85.
Rieppel O. 1995. Studies on skeleton formation in reptiles: implications for turtle relationships. Zoology-Analysis of Complex Systems 98: 298-308.
Rieppel O. & M. deBraga. 1996. Turtles as diapsid reptiles. Nature 384: 453-455.
Romer, A. S., 1967, Vertebrate Paleontology, University of Chicago Press; 3rd edition
Zardoya, R. and Meyer, A. 1998, Complete mitochondrial genome suggests diapsid affinities of turtles, Proc Natl Acad Sci U S A. 1998 November 24; 95(24): 14226–14231.

Pareiasaurus

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Pareiasaurus
Conservation status: Fossil
Fossil range: Mid Permian

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Order:	Procolophonomorpha
Suborder:	Procolophonia
Family:	Pareiasauridae
Genus:	Pareiasaurus

Species

P. baini
P. bombidens
P. russouwi
P. serridens

Pareiasaurus is an extinct genus of anapsid reptile from the Permian period. It was about 2,50 m (8 ft 4 in) long.

Pareiasaurus was a large quadruped with elephantine legs, walking in a semi-erect posture. Its skull had several spine- and wart-like protrusions. Pareiasaurus's leaf-shaped teeth, ideal for biting through tough plant fibers, indicate it was a herbivore. Even the pallet had teeth on it.

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Turtles

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Haeckel Chelonia "Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904

Turtles
Fossil range: Triassic - Recent
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Testudines, Linnaeus, 1758
Suborders: Cryptodira, Pleurodira

Turtles are reptiles of the order Testudines (all living turtles belong to the crown group Chelonia), most of whose body is shielded by a special bony or cartilagenous shell developed from their ribs. The Order Testudines includes both extant (living) and extinct species, the earliest turtles being known from the early Triassic Period, making turtles one of the oldest reptile groups, and a much more ancient group than the lizards and snakes. About 300 species are alive today. Some species of turtles are highly endangered. Like birds, turtles are able to detect the Earth's magnetic field with magnetosensors, which allow them to migrate.

Evolution of turtles

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The first turtles are believed to have existed in the Mesozoic, around 200 million years ago. Their exact ancestry is disputed. It was believed that they are the only surviving branch of the ancient clade Anapsida, which includes groups such as procolophonoids, millerettids, protorothyrids and pareiasaurs. All anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygomatic arch). Most anapsids became extinct in the late Permian period, except procolophonoids and possibly the precursors of the testudines (turtles).

However, it was recently suggested that the anapsid-like turtle skull may be due to reversion rather than to anapsid descent. More recent phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. All molecular studies have strongly upheld this new phylogeny, though some place turtles closer to Archosauria. Re-analysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa broadly enough for constructing the cladogram. Future analyses may show the turtles to be relatives of the placodonts.

A new phylogenetic analysis agrees with prior analyses nesting turtles with pareiasaurs within the much larger clade, Lepidosauromorpha. The closest pareiasaur to turtles appears to be a rarely-studied form, Stephanospondylus. Indeed turtles are related to other reptiles without temporal openings. They are also closer to lizards than they are to archosaurormophs, including placodonts.

The earliest known modern turtle is proganochelys, though this species already had many advanced turtle traits, and thus probably had many millions of years of preceding "turtle" evolution and species in its ancestry. It did lack the ability to pull its head into its shell (and it had a long neck), and had a long, spiked tail ending in a club, implying an ancestry occupying a similar niche to the ankylosaurs (though, presumably, only parallel evolution).

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

Physical description of turtles

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Turtles vary widely in size, although marine turtles tend to be relatively big animals. The largest chelonian is a marine turtle, the great leatherback sea turtle, which can reach a shell length of 200 cm (80 inches) and can reach a weight of over 900 kg (2,000 lb, or 1 short ton). Freshwater turtles are smaller, with the largest species being the Asian softshell turtle Pelochelys cantorii, which has been reported to measure up to 200 cm or 80 in (Das, 1991). This dwarfs even the better-known alligator snapping turtle, the largest chelonian in North America, which attains a shell length of up to 80 cm (31½ in) and a weight of about 76 kg (170 lb). Giant tortoises of the genera Geochelone, Meiolania, and others were relatively widely distributed around the world into prehistoric times, and are known to have existed in North and South America, Australia, and Africa. They became extinct at the same time as the appearance of Man, and it is assumed that humans hunted them for food. The only surviving giant tortoises are on the Seychelles and Galápagos Islands and can grow to over 130 cm (50 in) in length, and weigh about 300 kg (670 lb) [1].

The largest ever chelonian was Archelon ischyros, a Late Cretaceous sea turtle known to have been up to 4.6 m (15 ft) long [2].

The smallest turtle is the speckled padloper tortoise of South Africa. It measures no more than 8 cm (3 in) in length and weighs about 140 g (5 oz). Two other species of small turtles are the American mud turtles and musk turtles that live in an area that ranges from Canada to South America. The shell length of many species in this group is less than 13 cm (5 in) in length.

Some sea turtles have evolved gills near the anus to assist with respiration. These are distinct from the pharyngeal gills (which fish have, and which are lost during embryonic development in turtles).

Neck folding

Turtles are broken down into two groups, according to how they evolved a solution to the problem of withdrawing their neck into their shell (something the ancestral Proganochelys could not do): the Cryptodira, which can draw their neck in while folding it under their spine; and the Pleurodira, which have to fold their neck to the side.

Head

Most turtles and tortoises have eyes placed on the upper sides of their heads. Species of turtles that spend most of their life on land have their eyes looking down at objects in front of them. Some aquatic turtles, such as snapping turtles and soft-shelled turtles, have eyes closer to the top of the head. These species of turtles can hide from predators in shallow water where they lie entirely submerged except for their eyes and nostrils. Sea turtles possess glands near their eyes that produce salty tears that rids their body of excess salt taken in from the water they drink.

Turtles are thought to have exceptional night vision due to the unusually large amount of rod cells in their retinas. Normal daytime vision is marginal at best due to their color-blindness and poor visual acuity. In addition to daytime vision problems, turtles have very poor pursuit movement abilities, which is most likely due to the fact that pursuit movement abilities are normally reserved for predators that hunt quick moving prey.

Turtles have a rigid beak. Turtles use their jaws to cut and chew food. Instead of teeth, the upper and lower jaws of the turtle are covered by horny ridges. Their ancient ancestors have teeth unlike modern-day turtles. Carnivorous turtles usually have knife-sharp ridges for slicing through their prey. Herbivourous turtles have serrated edged ridges that help them cut through tough plants. Turtles use their tongues to swallow food, but they can't, unlike most reptiles, stick out their tongues to catch food.

Shell

The upper shell of the turtle is called the carapace. The lower shell that encases the belly is called the plastron. The carapace and plastron are joined together on the turtle's sides by bony structures called bridges. The inner layer of a turtle's shell is made up of about 60 bones that includes portions of the backbone and the ribs, meaning the turtle cannot crawl out of its shell. In most turtles, the outer layer of the shell is covered by horny scales called scutes that are part of its outer skin, or epidermis. Scutes are made up of a fibrous protein called keratin that also makes up the scales of other reptiles. These scutes overlap the seams between the shell bones and add strength to the shell. Some turtles do not have horny scutes. For example, the leatherback sea turtle and the soft-shelled turtles have shells covered with leathery skin instead.

The shape of the shell gives helpful clues to how the turtle lives. Most tortoises have a large dome-shaped shell that makes it difficult for predators to crush the shell between their jaws. One of the few exceptions is the African pancake tortoise which has a flat, flexible shell that allows it to hide in rock crevices. Most aquatic turtles have flat, streamlined shells which aid in swimming and diving. American snapping turtles and musk turtles have small, cross-shaped plastrons that give them more efficient leg movement for walking along the bottom of ponds and streams.

Tortoises have rather heavy shells in contrast to aquatic and soft-shelled turtles which have lighter shells that help them avoid sinking in water and swim faster and more agilely. These lighter shells have large spaces called fontanelles between the shell bones. The shell of a leatherback turtle is extremely light because they lack scutes and contain many fontanelles.

The color of a turtle's shell may vary. Shells are commonly coloured brown, black, or olive green. In some species, shells may have red, orange, yellow, or grey markings and these markings are often spots, lines, or irregular blotches. One of the most colorful turtles is the eastern painted turtle which includes a yellow plastron and a black or olive shell with red markings around the rim.

Skin and Moulting

As mentioned above, the outer layer of the shell is part of the skin, each scute (or plate) on the shell corresponding to a single modified scale. The remainder of the skin is composed of skin with much smaller scales, similar to the skin of other reptiles. Turtles and terrapins do not moult their skins all in one go, as snakes do, but continuously, in small pieces. When kept in aquaria, small sheets of dead skin can be seen in the water (often appearing to be a thin piece of plastic) when it has been sloughed off, often when the animal deliberately rubs itself against a piece of wood or stone. Tortoises also shed skin, but a lot of dead skin is allowed to accumulate into thick knobs and plates that provide protection to parts of the body outside the shell.

The scutes on the shell are never moulted, and, as they accumulate over time, the shell becomes thicker. By counting the rings formed by the stack of smaller, older scutes on top of the larger, newer ones, it is possible to estimate the age of a turtle, if you know how many scutes are produced in a year [3]. This method is not very accurate, partly because growth rate is not constant, but also because some of the scutes eventually fall away from the shell.

Limbs

Terrestrial tortoises have short, sturdy feet. Tortoises are famous for moving slowly, in part because of their heavy shell but also because of the relatively inefficient sprawling gait that they have, with the legs being bent, as with lizards rather than being straight and directly under the body, as is the case with mammals.

The amphibious turtles normally have limbs similar to those of tortoises except that the feet are webbed and often have long claws. These turtles swim using all four feet in a way similar to the dog paddle, with the feet on the left and right side of the body alternately providing thrust. Large turtles tend to swim less than smaller ones, and the very big species, such as aligator snapping turtles, hardly swim at all, preferring to simply walk along the bottom of the river or lake. As well as webbed feet, turtles also have very long claws, used to help them clamber onto riverbanks and floating logs, upon which they like to bask. Male turtles tend to have particularly long claws, and these appear to be used to stimulate the female while mating. While most turtles have webbed feet, a few turtles, such as the pig-nose turtles, have true flippers, with the digits being fused into paddles and the claws being relatively small. These species swim in the same way as sea turtles (see below)

Sea turtles are almost entirely aquatic and instead of feet they have flippers. Sea turtles "fly" through the water, using the an up-and-down motion of the front flippers to generate thrust; the back feet are not used for propulsion but may be used as rudders for steering. Compared with freshwater turtles, sea turtles have very limited mobility on land, and apart from the dash from the nest to the sea as hatchlings, male sea turtles normally never leave the sea. Females must come back onto land to lay eggs. They move very slowly and laboriously, dragging themselves forwards with their flippers. The back flippers are used to dig the burrow and then fill it back with sand once the eggs have been deposited.