Reptilia (Reptiles)


Reptiles are a diverse group of vertebrates, including turtles, crocodiles, lizards and snakes, as well as the extinct dinosaurs, pterosaurs, plesiosaurs and ichthyosaurs. Reptiles lay cleidoic eggs (adapted to dry land), and they include the ancestors of birds and mammals.

Key Concepts

  • The ‘Reptilia’ is a paraphyletic group that includes turtles, lizards, snakes and crocodilians but excludes descendant birds and mammals.
  • Reptiles include the majority of members of clade Amniota, the tetrapod group that lays eggs and are distinguished from amphibians by not having to lay eggs in water and by not having a larval stage for the young.
  • The amniotic egg, with extraembryonic membranes and an allantois to collect waste, is shared by all modern reptiles, birds and mammals.
  • Amniotes fall into two main clades based on their skull structure: diapsids with a double‐arched skull pattern and synapsids with a single, lower temporal opening; some amniotes either did not have temporal openings, or later lost them, the anapsid condition.
  • Diapsid amniotes arose in the Carboniferous, and include modern lizards, snakes, crocodilians, birds, plus extinct dinosaurs and pterosaurs.
  • Synapsid amniotes arose at the same time and include many extinct groups of so‐called mammal‐like reptiles, as well as mammals.
  • There are over 11 050 species of living reptiles, mainly living in the tropics because of their ectothermic (externally regulated) thermophysiology.

Keywords: reptiles; lizards; snakes; turtles; crocodiles; dinosaurs; ectothermy

Figure 1. Basic amniote characters. (a) The cleidoic egg, showing the semipermeable shell and the extraembryonic membranes. (b) The main skull patterns are seen in reptiles, and amniotes in general: anapsid, diapsid and synapsid. Abbreviations: j, jugal; p, parietal; po, postorbital; sq, squamosal. Based on various sources.
Figure 2. Basic design of a diversity of reptiles. (a) The basal amniote Paleothyris, from the Mid Carboniferous of Canada. (b) The living marine turtle Chelone seen from below, with the plastron removed. (c) The extinct synapsid Thrinaxodon, from the Early Triassic of South Africa. (d) The extinct crocodilian Protosuchus from the Early Jurassic of North America. (e) The living sphenodontid Sphenodon, the tuatara. Based on various sources.
Figure 3. Phylogeny of the Amniota, focusing on the major groups of reptiles, their fossil history and current diversity. 1, Pareiasauridae; 2, Procolophonidae. The ‘?’ indicates uncertainty about the initial divergences among diapsids.


Benson RBJ (2012) Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies. Journal of Systematic Palaeontology 10: 601–624.

Benton MJ (1985) Classification and phylogeny of the diapsid reptiles. Zoological Journal of the Linnean Society 84: 97–164.

Benton MJ, Forth J and Langer MC (2014) Models for the rise of the dinosaurs. Current Biology 24: R87–R95.

Brocklehurst RJ, Schachner ER, Codd JR and Sellers WI (2020) Respiratory evolution in archosaurs. Philosophical Transactions of the Royal Society B 375: 20190140.

Carroll RL (1969) A middle Pennsylvanian captorhinomorph and the interrelationships of primitive reptiles. Journal of Paleontology 43: 151–170.

Ford DP and Benson RJB (2020) The phylogeny of early amniotes and the affinities of Parareptilia and Varanopidae. Nature Ecology & Evolution 4: 57–65.

Gauthier J, Kluger AG and Rowe T (1988) Amniote phylogeny and the importance of fossils. Cladistics 4: 105–209.

Hedges SB and Poling LL (1999) A molecular phylogeny of reptiles. Science 283: 998–1001.

Laurin M and Reisz RR (1995) A reevaulation of early amniote phylogeny. Zoological Journal of the Linnean Society 113: 165–223.

Laurin M (2005) Embryo retention, character optimization, and the origin of the extraembryonic membranes of the amniotic egg. Journal of Natural History 39: 3151–3161.

Pincheira‐Donoso D, Bauer AM, Meiri S and Uetz P (2013) Global taxonomic diversity of living reptiles. PLoS ONE 8: e59741.

Pritchard AC and Nesbitt SJ (2017) A bird‐like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida. Royal Society Open Science 4: 170499.

Schoch RR and Sues H‐D (2016) The diapsid origin of turtles. Zoology 119: 159–161.

Seebacher F and Franklin CE (2005) Physiological mechanisms in thermoregulation of reptiles. Journal of Comparative Physiology B 175: 533–541.

Shine R (1983) Reptilian reproductive modes: the oviparity–viviparity continuum. Herpetologica 39: 1–8.

Stubbs TL and Benton MJ (2016) Ecomorphological diversifications of Mesozoic marine reptiles: the roles of ecological opportunity and extinction. Paleobiology 42: 547–573.

Further Reading

Bellairs AA d' (1969) The Life of Reptiles, vol. 2. Weidenfeld & Nicolson: London.

Benton MJ (2015) Vertebrate Palaeontology, 4th edn. Wiley: New York.

Gans C, Gaunt AS and Adler K (eds) (1969) Biology of the Reptilia, vol. 24. Society for the Study of Amphibians and Reptiles: New York, NY.

Pough FH et al. (2015) Herpetology, 4th edn. Sinauer: New York, NY.

Pough FH and Janis CM (2018) Vertebrate Life, 10th edn. Oxford University Press: New York, NY.

Sues H‐D (2009) The Rise of Reptiles: 320 Million Years of Evolution. Johns Hopkins University Press: Baltimore, MD.

Vitt LJ (2013) Herpetology: An Introductory Biology of Amphibians and Reptiles, 4th edn. Academic Press: New York, NY.

Weishampel DB, Osmólska H and Dodson P (eds) (2004) The Dinosauria, 2nd edn. University of California Press: Berkeley, CA.

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Benton, Michael J(Oct 2020) Reptilia (Reptiles). In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0029215]