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| Reptiles Temporal range: Carboniferous – Recent |
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| A Tuatara, Sphenodon punctatus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Sauropsida Goodrich, 1916 |
| Living orders | |
| Synonyms | |
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Reptile is the common name for one of the main groups of land vertebrates. It is not used so much by biologists, who use more accurate terms.
The name "reptile" comes from Latin and means "one who creeps". All living reptile species are cold blooded, have scaly skin, and lay cleidoic eggs. They excrete uric acid (instead of urea), and have a cloaca. A cloaca is a shared opening for the anus, urinary tract and reproductive ducts. Reptiles also share an arrangement of the heart and major blood vessels which is different from that of mammals.
Many important groups of reptiles are now extinct. The great marine reptiles of the Mesozoic era, the ichthyosaurs, plesiosaurs and mosasaurs, are extinct. We used to say the dinosaurs were extinct, but they survive in the form of their feathered descendants (birds). Ancient reptiles that do survive include the turtles, the crocodiles and the Tuatara, the lone survivor of its group. The great majority of present-day reptiles are snakes and lizards.
The study of living reptiles is called herpetology.
Some reptiles are more closely related to birds than they are to other reptiles. Crocodiles are more closely related to birds than they are to lizards. Theropod dinosaurs are even more closely related, because birds evolved from them.
Cladistic writers prefer a more unified (monophyletic) grouping. This puts the birds (over 10,000 species) with what people normally call reptiles. (see Sauropsida)
Reptilia is an evolutionary grade rather than a clade. The main reason is that the term 'reptile' does not include birds, the descendents of theropod dinosaurs. Another reason is that the word 'reptile' is misleading because many extinct types were very different from living reptiles.
So instead of Reptilia as a taxonomic class, today most experts use Class Sauropsida (which includes all reptiles and birds, living and extinct). Class Synapsida includes mammals and all their forebears. Reptile is still the usual informal term to describe living snakes and lizards. Mammals are a genuine clade, and so Mammalia is still the taxonomic term.
Since reptiles are not monophyletic, reclassifying them is one of the key aims of researchers. Some taxonomists, such as Benton, make Sauropsida and Synapsida as class-level taxa. The two groups split in the Carboniferous, from stem-group Amniotes (the early tetrapods, which laid cleidoic eggs).
Chameleons, a lizard
Komodo dragon, sleeping. Largest living lizard
Reptiles, from Nouveau Larousse Illustré, 1897-1904: Notice the inclusion of amphibians (below the crocodiles).
An "antediluvian monster", a Mosasaurus discovered in a Maastricht limestone quarry, 1770 (contemporary engraving)
Phylogenetic classifications group the traditional "mammal-like reptiles", like this Varanodon, with other synapsids, not with extant reptiles.
Mesozoic scene showing typical reptilian megafauna: dinosaurs including Europasaurus holgeri, iguanodonts and Archaeopteryx lithographica perched on the foreground tree stump.
A = Anapsid, B = Synapsid, C = Diapsid
Sustained energy output (joules) of a typical reptile versus a similar size mammal as a function of core body temperature. The mammal has a much higher peak output, but can only function over a very narrow range of body temperature.
Red-eared slider taking a gulp of air
Skin of a sand lizard, showing squamate reptiles iconic scales
A colubrid snake, Dolichophis jugularis, eating a legless lizard, Pseudopus apodus. Most reptiles are carnivorous, and many primarily eat other reptiles.
Most reptiles reproduce sexually, for example this Trachylepis maculilabris skink
A camouflaged Phelsuma deubia on a palm frond
A White-headed dwarf gecko with shed tail
The 1897 painting of fighting "Laelaps" (now Dryptosaurus) by Charles R. Knight
An early reptile Hylonomus
Varanus priscus was a giant carnivorous goanna lizard, perhaps as long as 7 metres and weighing up to 1,940 kilograms.
Thermographic image of monitor lizards
