Reptile

? Reptiles
Eastern Herman's Tortoise
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Reptilia Linnaeus, 1758
Extant Orders
Testudines - Turtles  Rhynchocephalia - Tuataras  Squamata   Suborder Sauria- Lizards   Suborder Orphidia (Serpentes) - Snakes   Suborder Amphisbaenia - Worm lizards  Crocodylia - Crocodilians

Reptiles are tetrapods (four-legged vertebrates) and amniotes (animals whose embryos are surrounded by an amniotic membrane that encases it in amniotic fluid). Reptiles have traditionally been defined as including all the amniotes except birds and mammals.

Today, reptiles are represented by four surviving orders:

• Crocodilia (crocodiles, caimans, and alligators)
• Rhynchocephalia (tuataras from New Zealand)
• Squamata (lizards, snakes and amphisbaenids ("worm-lizards"))
• Testudines (turtles)

According to a report by Uetz in 2000, comprehensive compilations reveal a total of 7,870 species of reptiles, with the majority being lizards (4,470 species) and snakes (2,920), and with 23 described species of living crocodiles, 295 species of living turtles, 156 amphisbaenians, and 2 species of tuataras. Uetz reported that 51% of known reptile species belong to one of three families: colubrid snakes (1,850 species), skinks (1,200), and geckos (1,000). New reptile species continue to be described at the rate of about 60 species per year (Uetz 2000).

A subsequent tabulation by Uetz in 2005 showed a total of 8,240 extant reptile species, and his March 2006 list revealed 8,364 known species. The International Union for the Conservation of Nature and Natural Resources (IUCN) tabulated 8,163 described species of reptiles in 2004.

A herpetologist is a zoologist who studies reptiles and amphibians.

Overview

Reptiles are found on every continent except for Antarctica, although their main distribution comprises the tropics and subtropics. Uetz (200) reported 2100 living species of reptiles in Asia (including new Guinea), 1550 in South America, 1350 in Africa, 1050 in Central America, and 850 in Australia. There were but 190 species of living reptiles in Europe and 360 in North America.

Though all cellular metabolism produces some heat, modern species of reptiles do not generate enough to maintain a constant body temperature and are thus referred to as "cold-blooded" (ectothermic). (TheLeatherback Sea Turtle is an exception: a reptile that elevates its body temperature well above that of its surroundings.) Instead they rely on gathering and losing heat from the environment to regulate their internal temperature, such as 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 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 some members of the Testudines, all reptiles are covered by scales.

Systems

Circulatory system

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). 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).

Greek tortoise of North-East Turkey

Respiratory system

All reptiles breathe using lungs. Aquatic turtles have developed more permeable skin, and for some species even gills in their anal region (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 a way around it. Varanids, and a few other lizard species, employ buccal pumping (a method of respiration using the throat muscles) as a complement to their normal 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."

The turtles and tortoises have found a variety of solutions to breathing, given 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 red-eared sliders 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 (Landberg et al. 2003).

Most reptiles lack a secondary palate, meaning that they must hold their breath while swallowing. Crocodylians 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 have a different approach and extended their trachea instead. Their tracheal extension sticks out like a fleshy straw. By thrusting their windpipe into the throat, these animals can swallow large prey without suffering from asphyxiation, despite the fact that swallowing may take several hours.

Digestion and excretory system

Land-dwelling reptiles, such as snakes and lizards, extrete nitrogenous wastes in pasty or dry form as crystals of uric acid (Towle 1989). Two small kidneys are used in excretion.

Snakes have hinged upper and lower jaws, which move independently. These jaws stretch when unhinged, allowing snakes to swallow large prey. Saliva begins to digest food before it reaches the stomach, which is bascially an enlargement at the end of the esophogus where digestion can slowly proceed (Towle 1989).

Crocodilians have modified salivary glands on their tongue, salt glands, used for excreting excess salt from their body, although they are non-functioning in alligators and caimans. Crocodilians are known to swallow stones, gastroliths ("stomach-stones"), which help to crush up the bones of their prey. The crocodile stomach is divided into two chambers, the first one is described as being powerful and muscular, like a bird gizzard, adn 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.

Nervous system and senses

Reptiles have an advanced nervous system compared to amphibians. They have twelve pairs of cranial nerves. The brain is relatively small.

Crocodilians see well at day and may even have color vision; their vertical, cat-like pupil gives them excellent night vision.

In crocodilians, the upper and lower jaws are covered with sensory pits, the crocodile version of the lateral organ we see in fish and many amphibians. 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. While alligators and caimans only have them on their jaws, crocodiles have similar organs on almost every scale on their body

Reproductive system

Most reptiles reproduce sexually. Many male snakes rely on scent to find females, with fertilization being internal.

However, sexual 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 (expecially Aspidocelis) and lacertids (Lacerta). Parthenogentic species are also suspected to occur among chameleons, agamids, xantusiids, and typhlopids.

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, just like mammals (Pianka and Vitt 2003). They often provide considerable initial care for their hatchlings.

Amniotic eggs covered with leathery or calcareous shells. Amnionic eggs consist of four membranes: (1) the amnion (thin membrane that encloses the amnion fluid within which the embryo rests), (2) the yolk sac (enclosing the yolk, the protein-rich food for the embryo), the (3) allantois (which stores the nitrogenous wastes until hatching), and (4) the chorion (the outer membrane that lines the shell) (Towle 1989). Eggs are waterproof but permeable to gases. Sperm are placed inside the female by internal fertilization prior to the formation of the shell.

In some reptiles, the sex of the juvenile is determined by the incubation temperature.

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, Araeoscelis, Paleothyris, Ophiacodontidae, Archaeothyris, mesosaurs, and Ophiacodon are other examples of fossil animals considered to be ancient reptiles.

The first true "reptile" or Amniotes are categorized as anapsids. Anapsids (Anapsida) are vertebrates characterized by solid skulls without openings near the temples, but with holes in the skull only for nose, eyes, spinal cord, etc. Turtles are believed by some to be surviving anapsids, indeed the only surviving anapsids, as they also share this skull structure. However, this point has become contentious, with some arguing that turtles reverted to this primitive state in the process of improving their armor. Both sides have marshalled evidence, and the conflict has yet to be resolved.

Shortly after the appearance it the fossil recored of the first reptiles, two branches appeared in the fossil record. One lead to the Anapsidia, which did not develop holes in their skulls, and the other to the Diapsida (diapsids), which possessed a pair of holes in their skulls behind the eyes, along with a second pair located higher on the skull. Diapsids ("two arches") are a group of tetrapod animals that appeared in the fossil record about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and are considered to include all birds, crocodiles, lizards, snakes, and tuataras (and possibly even turtles). While some lost either one hole (lizards), or both holes (snakes), they are still classified as diapsids based on their ancestry

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 containing pterosaurs and dinosaurs).

The earliest, solid-skulled amniotes are also considered to have given rise to a separate line, the Synapsida (synapsids). Synapsids developed a pair of holes in their skulls behind the eyes (similar to the diapsids), which have the advantage of lightening the skull and increasing the space for jaw muscles. The synapsids eventually evolved into mammals, and are often referred to as mammal-like reptiles.

Classification of reptiles

As noted above, 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 are considered to have developed from the original reptile. Colin Tudge (2000) 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'.

Some cladists thus redefine Reptilia as a monophyletic group, including both the classic reptiles as well as the birds and perhaps the mammals (depending on ideas about their relationships). Others abandon it as a formal taxon altogether, dividing it into several different classes. However, other biologists believe that the common characters of the standard four orders are more important than the exact relationships, or feel that redefining the Reptilia to include birds and mammals would be a confusing break with tradition. A number of biologists have adopted a compromise system, marking paraphyletic groups with an asterisk, e.g. class Reptilia*. Colin Tudge (2000) notes other uses of this compromise system:

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.

College-level references, such as Benton (2004), 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.

Termiology: Sauropsida versus Synapsida

The terms Sauropsida ("Lizard Faces") and Theropsida ("Beast Faces") were coined to distinguish between lizards, birds, and their relatives on one hand (Sauropsida) and mammal-like reptiles and mammals (Theropsida) on the other. This classification supplemented, but was never as popular as the classification of the reptiles according to the positioning of temporal fenestrae mentioned above under evolution of the reptiles (Anapsida, Diapsida, Synapsida, etc.)

A diverse group of egg-laying vertebrate animals, the Sauropsida includes all modern and most extinct "reptiles" (excluding synapsids). Living sauropsids include lizards, snakes, turtles, crocodiles and birds. Extinct sauropsids include dinosaurs (excepting birds), pterosaurs, plesiosaurs, Ichthyosaurs, and many others.

The synapsids were originally defined, at the turn of the 20th Century, as one of the five main subclasses of reptiles, on the basis of their distinctive temporal openings. The synapsids represented the reptilian lineage that led to the mammals, and gradually evolved increasingly mammalian features, hence, "mammal-like reptiles." The traditional classification continued through to the late 1980s.

In the current cladistic based system, the Linnean classification of the Class Reptilia in terms of four sub-classes has been replaced. "Sauropsid" (as a monophyletic clade) is retained to refer to all non-synapsid amniotes (or just replaced by "Reptilia" even though the sauropsid group includes birds). The term "Theropsida" is replaced by Synapsida, which now refers to both the old subclass Synapsida and the mammals. In the new (2004) edition of his textbook, Dr Michael Benton uses the term "Class Sauropsida" to refer to all non-synapsid reptiles. Because Synapsids evolved into mammals, the mammals therefore are included under the Clade Synapsida. That is, "synapsids" are now also known as "theropsids."

Reptile classification according to Benton (2000)

The following is a very abbreviated classification of the extensive classification system presented by Benton (2000).

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

Classification of extant reptiles by Uetz (2005)

The following classification of living reptiles was given by Uetz (2005), which was modified from the overall taxonomy of Zug et al. (2001), and with the Iguania mainly after Frost et al. (2001) and the turtles mainly after Fujita et al. (2004).

Subclass Anapsida

• Order Testudines - Turtles (phylogeny)
  • Suborder Cryptodira
    • Family Chelydridae (Snapping Turtles)
    • Superfamily Testudinoidea
      • Family Emydidae (Pond Turtles/Box and Water Turtles)
      • Family Testudinidae (Tortoises)
      • Family Geoemydidae (Bataguridae) (Asian River Turtles, Leaf and Roofed Turtles, Asian Box Turtles)
    • Superfamily Trionychoidea
      • Family Carettochelyidae (Pignose Turtles)
      • Family Trionychidae (Softshell Turtles)
    • Superfamily Kinosternoidea
      • Family Dermatemydidae (River Turtles)
      • Family Kinosternidae (Mud and Musk Turtles)
    • Superfamily Chelonioidea
      • Family Cheloniidae (Sea Turtles)
      • Family Dermochelyidae (Leatherback Turtles)
  • Suborder Pleurodira (phylogeny)
    • Family Chelidae (Austro-American Sideneck Turtles)
    • Superfamily Pelomedusoidea
      • Family Pelomedusidae (Afro-American Sideneck Turtles)
      • Family Podocnemididae (Madagascan Big-headed and American Sideneck River Turtles)

Subclass Archosauria

• Order Crocodylia - Crocodiles, caimans, alligators
  • Suborder Eusuchia
    • Family Crocodylidae (Crocodylians)

Subclass Lepidosauria

• Order Rhynchocephalia
  • Suborder Sphenodontida
    • Family Sphenodontidae (Tuataras)
• Order Squamata
  • Suborder Sauria (Lacertilia) - Lizards (phylogenies1 and 2)
    • Infraorder Iguania
      • Family Agamidae (Agamas)
      • Family Chamaeleonidae (Chameleons)
      • Family Iguanidae ("Iguanas") [Pleurodonta]
    • Infraorder Gekkota
      • Family Gekkonidae (Geckoes)
      • Family Pygopodidae (Legless Lizards)
      • Family Dibamidae (Blind Lizards)
    • Infraorder Scincomorpha
      • Family Cordylidae (Spinytail Lizards)
      • Family Gerrhosauridae (Plated Lizards)
      • Family Gymnophthalmidae (Spectacled Lizards)
      • Family Teiidae (Whiptails and Tegus)
      • Family Lacertidae (Lacertids, Wall Lizards)
      • Family Scincidae (Skinks)
      • Family Xantusiidae (Night Lizards)
    • Infraorder Diploglossa
      • Family Anguidae (Glass Lizards and Alligator Lizards; Lateral Fold Lizards)
      • Family Anniellidae (American Legless lizards)
      • Family Xenosauridae (Knob-scaled Lizards)
    • Infraorder Platynota (Varanoidea)
      • 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 (Serpentes) - Snakes (phylogeny)
      • Superfamily Typhlopoidea (Scolecophidia)
        • Family Anomalepidae (Dawn Blind Snakes)
        • Family Typhlopidae (Blind Snakes)
        • Family Leptotyphlopidae/Glauconiidae (Slender Blind Snakes)
      • Superfamily Henophidia (Boidea)
        • Family Aniliidae/Ilysiidae (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 incl. Ungaliophiidae (Dwarf Boas)
        • Family Uropeltidae (Shield-tail Snakes)
        • Family Xenopeltidae (Sunbeam Snakes)
      • Superfamily Xenophidia (Colubroidea = Caenophidia)
        • Family Acrochordidae (File Snakes)
        • Family Atractaspididae (Mole Vipers)
        • Family Colubridae (Colubrids) (20 KB !)
        • Family Elapidae (incl. Hydrophiidae; Cobras, Kraits, Coral Snakes, Sea Snakes)
        • Family Viperidae (Vipers and Pit Vipers)

References

ISBN links support NWE through referral fees

• Zug, G. R., L. J. Vitt, and J. P. Caldwell. 2001. Herpetology, 2nd ed. San Diego: Academic Press.

• 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 pages).

• Fujita, M. K., T. N. Engstrom, D. E. Starkey, and H. B. Shaffer. 2004. Turtle phylogeny: insights from a novel nuclear intron. Molecular Phylogenetics and Evolution 31(3):1031-1040

• Bauer, A. M. 1999. Twentieth century amphibian and reptile discoveries. Cryptozoology 13:1-17.
• Benton, M. J. 2004. Vertebrate Paleontology, 3rd edition. Blackwell Science Ltd
• Colbert, E. H. 1969. Evolution of the Vertebrates, 2nd edition. New York: John Wiley and Sons Inc.
• Eschmeyer, W. N., C. J. Ferraris, and M. D. Hoang. 1998. Catalogue of Fishes, 3 Volumes. San Francisco: California Academy of Science.
• Glaw, F., and J. Kohler. 1998. Amphibian species diversity exceeds tat of mammals. Herpetological Review 29(1):11-12.
• Uetz, P. 2000. How many reptile species? Herpetological Review 31(1):13-15.
• Uetz, P. 2005. The EMBL Reptile Database. http://www.embl-heidelberg.de/~uetz/db-info/SpeciesStat.html

• 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, 116-118, University of California Press. 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.

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