Reptile is the common name for one of the main groups of landvertebrates. It is not used so much by biologists, who use more accurate terms.
The name "reptile" comes fromLatin and means "one who creeps". All living reptile species arecold blooded, have scalyskin, and laycleidoic eggs.[1][2] They excreteuric acid (instead ofurea), and have acloaca. A cloaca is a shared opening for theanus, urinary tract and reproductive ducts. Reptiles also share an arrangement of theheart and major blood vessels which is different from that of mammals.[3] Birds have all of these features.
Many important groups of reptiles are nowextinct, for example themosasaurs. We used to say thedinosaurs were extinct, but they survive in the form of their feathered descendants (birds). Ancient reptiles that do survive include theturtles, thecrocodiles and theTuatara, the lone survivor of its group. The great majority of present-day reptiles aresnakes andlizards.
The study of living reptiles is calledherpetology.
Some reptiles are more closely related tobirds than they are to other reptiles. Crocodiles are more closely related to birds than they are to lizards.Theropoddinosaurs are even more closely related, because birds evolved from them.
Cladistic writers prefer to put the birds (over 10,000 species) with what people usually call reptiles.[4][5][6] (seeSauropsida)
Reptilia is anevolutionary grade rather than aclade. The main reason is that the term 'reptile' does not include birds, the descendents oftheropoddinosaurs. 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 many experts use ClassSauropsida (which includes all reptiles and birds, living and extinct). ClassSynapsida includes mammals and all their forebears.Reptile is still the usualinformal term to describe livingsnakes andlizards. Mammals are a genuine clade, and so Mammalia is still the taxonomic term.
Since reptiles are notmonophyletic, reclassifying them is one of the key aims of researchers.[4][7][8] Some taxonomists, such as Benton,[9] make Sauropsida and Synapsida class-leveltaxa. The two groups split in theCarboniferous, from stem-groupAmniotes (the earlytetrapods, which laidcleidoic eggs).
Amembrane forms an innereyelid in reptiles and birds. Whitish or translucent, it can be drawn across the eye to protect it from dust and keep it moist. It is called thenictitating membrane.
Reptiles can live in large and small sizes. Their land sizes can be both bigger and smaller than mammals.Titanosaurs were the largest land reptiles, and the smallest land reptile is achameleon 13.5mm long.[10]
↑Some give birth to live young, with the cleidoic eggs developing internally.
↑2008. "Squamata Suborder: Serpentes". The University of Georgia Museum of Natural History.Archived 2010-06-13 at theWayback Machine
↑Goodrich E.S. 1930.Studies on the structure and development of vertebrates. Macmillan, London.
12Gauthier J.A., Kluge A.G & Rowe T. 1988. The early evolution of the Amniota. pp103–155 in Michael J. Benton (ed)The phylogeny and classification of the tetrapods, Volume 1: Amphibians, Reptiles, Birds.Systematics Association, Special vol 35A. Clarendon Press, Oxford.
↑Modesto, S.P. (1999). "Observations of the structure of the Early Permian reptileStereosternum tumidum Cope".Palaeontologia Africana.35:7–19.
↑Gauthier J.A. 1994. The diversification of the amniotes. In D.R. Prothero and R.M. Schoch (eds)Major features of vertebrate evolution. 129-159. Knoxville, Tennessee: The Paleontological Society.
