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What are the Major Groups of Reptile?

Michael Anissimov
Updated May 21, 2024
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Reptiles, also known as Class Reptilia, Class Sauropsida, or merely sauropsids, are ectothermic ("cold-blooded" -- though this term has now fallen out of fashion) animals covered in scales. There are over 8,200 reptile species, about 50% more than their relatives, the mammals. The reptile is one of the few taxonomic classifications among tetrapods that are polyphyletic -- meaning the group deviates from the convention of including all descendants of a common ancestor. Birds are actually descendants from ancient reptiles, the dinosaurs, but are not considered reptiles. If birds were included in Reptilia, the group would be monophyletic.

Reptiles are one of two amniote groups, the other being the synapsids, represented today by the mammals. Amniotes nurture their embryos using a series of complex membranes. By contrast, amphibians, that is, non-amniotes, have simple eggs that must be laid in water.

Reptiles and the ancestors of mammals, the synapsids, split from each other a very long time ago. The earliest known reptile, Hylonomus, and the earliest known synapsid, Archaeothyris both lived during the Late Carboniferous period, about 315 million years ago. They both superficially resembled small lizards, but gave rise to radically different descendants. Synapsids and sauropsids have since alternated in their domination of the Earth, with synapsids ruling from the Carboniferous until the Permian-Triassic extinction about 251 million years ago. From then on out, dinosaurs began to evolve, and the balance tipped back in favor of the reptile. That is why this period of time was called the Age of Reptiles. After the Cretaceous-Tertiary extinction 65 million years ago, all non-avian dinosaurs were obliterated, and synapsids, in the form of mammals, took over again.

There are four living Orders of reptile: Crocodilia (crocodiles, alligators, caimans, and gharials, 23 species), Sphenodontia (tuatara from New Zealand, 2 species), Squamata (lizards, snakes and amphisbaenids ("worm-lizards"), about 7,900 species) and Testudines (turtles and tortoises, about 300 species). The tuatara is considered a living relic, and is a popular subject of study among the phylogenetic and taxonomic communities.

The relationship between reptile groups can be confusing. Testudines either split off very early or is more closely related to the others: we don't know. Turtles lack holes in their skull, which is similar to some of the early reptiles, but they may have lost their skull holes more recently. Aside from Testudines, there are two main groups: archosaurs, which includes crocodilians and dinosaurs (including birds, which are descended from dinosaurs) and lepidosaurs, which includes everything else.

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Michael Anissimov
By Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.
Discussion Comments
By ValleyFiah — On May 29, 2011

I am taking a road trip from Maryland to Orlando, and I was hoping if someone could tell me where the best reptile stores are along the way. I am looking to buy a new snake, and I want to find a store (or breeder) with a large assortment of some rare and advanced breeds. I have a few snakes that I have had for about seven years, and I think I would like to add one more to the collection. I have a pinstripe ball python, a corn snake, and a blue morph tree python, all captive bred and healthy. I would appreciate any advice.

By istria — On May 28, 2011

@babalaas- When it comes to reptile habitats, the chameleon habitat is an advanced habitat compared to other animals. Chameleons will vary in their needs by species, but for the most part, they are arboreal reptiles that have a few common needs.

Chameleon habitats need to be large with plenty of foliage and tree limbs to climb on. Chameleons also need plenty of full spectrum light, warmth, and good ventilation. Some chameleons also need a high humidity enclosure. Finally, Chameleons need a source of dripping water for drinking.

If you can keep a chameleon happy, It can live about 10 years. This means that it must be fed a protein and mineral rich diet, live a fairly stress free life, and have the occasional outdoor enclosure experience to bask in natural light and ventilation (at least a few times a week). Chameleons are a labor intensive pet, but if you have the patience, you will be rewarded with a stunningly unique animal for a decade.

By Babalaas — On May 26, 2011

I want to buy a chameleon, but I would like to study them a little more before I make an impulse decision. I do not want to be an irresponsible pet owner that abandons a pet after a year or two.

What are the most important features of a reptile enclosure? Do chameleons have any special needs for their habitats? How long do they live?

Michael Anissimov
Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology...
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