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Lepidosauria
The Lepidosauria (from Greek meaning ''scaled lizards'') are reptiles with overlapping scales. This subclass includes Squamata and Rhynchocephalia. It is a monophyletic group and therefore contains all descendents of a common ancestor.〔Evans, S.E., Jones, M.E.H. 2010. The Origin, early history and diversification of lepidosauromorph reptiles. In Bandyopadhyay S. (ed.), "New Aspects of Mesozoic Biodiversity, 27 Lecture Notes," in ''Earth Sciences'' 132, 27-44. DOI 10.1007/978-3-642-10311-7_2〕 Squamata includes snakes, lizards, and amphisbaenia.〔Pyron RA, Burbrink FT, Wiens JJ: A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology 13:93.〕 Rhynchocephalia was a widespread and diverse group 220-100 million years ago;〔Jones, M.E.H. 2009. Dentary tooth shape in ''Sphenodon'' and its fossil relatives (Diapsida: Lepidosauria: Rhynchocephalia). Frontiers of Oral Biology 13: 9–15.〕 however, it is now represented only by the genus ''Sphenodon'', which contains two species of tuatara, native to New Zealand.〔Hay, J.M., Sarre, S.D., Lambert, D.M., Allendorf, F.W., and Daugherty, C.H. 2010. Genetic diversity and taxonomy:a reassessment of species designation in tuatara (Sphenodon: Reptilia). Conservation Genetics 11:1063-1081.〕〔Jones, M.E.H., Cree, A. 2012. Tuatara. Current Biology 22: 986–987 DOI: 10.1016/j.cub.2012.10.049〕 Lepidosauria is the sister taxon to Archosauria, which includes Aves and Crocodilia. Lizards and snakes are the most speciose group of Lepidosaurs and, combined, contain over 9,000 species.〔Uetz P (2010) The original descriptions of reptiles. 'Zootaxa' 2334: 59-68.〕 There are many noticeable distinguishing morphological differences between lizards, tuataras, and snakes.
==Diagnosis==
The reptiles in the subclass Lepidosauria can be distinguished from other reptiles by a variety of characteristics.〔Evans, S.E. 2003. At the feet of the dinosaurs: the early history and radiation of lizards. Biological Reviews, 78:513-551. doi:10.1017/S1464793103006134〕 First, the males have evolved a hemipenis instead of a single penis with erectile tissue that is found in crocodilians, birds, mammals, and turtles. The hemipenis can be found in the base of the tail. The tuatara has not fully evolved the hemipenis, but instead has shallow paired outpocketings of the posterior wall of the cloaca that have been determined to be precursors to the hemipenis.〔Pough, Harvey, et al. Herpetology. New Jersey: Prentice-Hall, 1998.〕
Second, most Lepidosaurs have the ability to autotomize their tails. However, this trait has been lost on some recent species. In lizards, fracture planes are present within the vertebrae of the tail that allow for its removal. Some lizards have multiple fracture planes, while others just have one single fracture plane. The regrowth of the tail is not always complete and is made of a solid rod of cartilage rather than individual vertebrae.〔Pough, Harvey, et al. Herpetology. New Jersey: Prentice-Hall, 1998.〕 In snakes, the tail separates between vertebrae and some do not experience regrowth.〔
Third, the scales in lepidosaurs are horny (keratinized) structures of the epidermis, allowing them to be shed collectively, contrary to the scutes seen in other reptiles.〔 This is done in different cycles, depending on the species. However, lizards generally shed in flakes while snakes shed in one piece. Unlike scutes, lepidosaur scales will often overlap like roof tiles.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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