Added December 2004.

Class Reptilia


The following is a more detailed listing of Class Reptilia. It includes those known extinct members, since these outnumber the living species and also give some guide to the relationships between dinosaurs, living reptiles, birds and mammals.

One of the major characteristics used to classify reptiles is the number of openings, or temporal fossae, in the skull. These large openings arose early on in reptilian life and allowed the jaw muscles to extend through them and be anchored onto the outside of the dermocranium. This in turn gave greater power to the jaws. The lack of temporal fossae should not be associated with backwardness, however: the turtles and tortoises of today, considered to be the more intelligent representatives of the Reptilia, all have anapsid skulls.

The dinosaurs are divided into two main orders based on the arrangement of the hip bones.

The listing given here is a fairly traditional one, and readers should note a couple of areas of difference: firstly, the Rhynchocephalia are not always recognised, and the tuatara considered instead as a suborder of the Squamata, along with lizards, snakes and amphisbaenians: secondly, the cladistic approach considers the birds to be a sister group of the Crocodilia and direct descendants of the dinosaurs. While there is a strong case for both these latter assertions (and in the nineteenth century the similarities had already been noted), it seems naturally difficult for most people to suddenly start regarding feathered creatures as the same type as scaled creatures, and so Class Aves (the birds) is traditionally regarded as separate from Class Reptilia.

Links are provided to the living families, about which information is provided elsewhere on the site. The rest of the groups listed here are extinct.

Anapsida     Temporal fossae lacking
  Captorhinomorpha Includes romeriids, earliest known reptiles
  Cotylosauria Large herbivores descended from captorhinomorpha
  Mesosauria Amphibious, with webbed feet, flattened tails and long narrow jaws with slender teeth: about 1m (3ft) long
  Testudinata/Chelonia Turtles and tortoises
    Cryptodira Chelonians retracting their head straight back
    Pleurodira Chelonians retracting their head sidewards
Synapsida     1 pair of temporal fossae below the squamosal bone
  Pelycosauria Mammal-like dentition
  Therapsida Mammal-like and ancestral to mammals
Euryapsida     1 pair of temporal fossae above the squamosal bone
  Protosauria Small lizard-like creatures
  Sauropterygia Paddle-limbed marine reptiles
  Plesiosauria Marine with flippers and often long necks
  Ichthyosauria Marine with fish-shaped bodies: may alternatively be considered a subclass
Lepidosauria     Primitive diapsids with 2 pairs of temporal fossae and scaly skins
  Eosuchia Common ancestor to lepidosaurs and possibly also to archosaurs
  Rhynchocephalia Lizard-like creatures: only 1 living species
  Squamata Modern reptiles, all of which periodically shed their skin
    Lacertilia/Sauria Lizards
    Ophidia/Serpentes Snakes
    Amphisbaenia Amphisbaenians or "worm lizards"
Archosauria     Advanced diapsids with 2 pairs of temporal fossae
  Thecodontia Teeth in sockets; originated bipedality; ancestral to dinosaurs
  Phytosauria Aquatic crocodile-like predators
  Crocodilia Quadrupedal, short-legged amphibious predators: largest living reptiles
  Saurischia Reptile-hipped dinosaurs having pubic symphysis
    Theropoda Carnivorous bipeds, including ancestors of birds
    Sauropodomorpha Quadrupedal herbivores, often reaching gigantic sizes
  Ornithischia Bird-hipped dinosaurs lacking pubic symphysis, usually herbivorous and quadrupedal
    Hadrosauria Bipedal, mostly duck-billed and amphibious
    Stegosauria Dorsal series of erect plates
    Ankylosauria Short-legged heavily-armoured
    Ceratopsia Bony head shield and horns
  Pterosauria Winged reptiles


Zoology, the Animal Kingdom: A complete course in 1000 questions and answers, Nancy M Jessop, McGraw-Hill, 1995. A very useful and readable course in zoology, although modern concepts such as cladistics are not covered. The table above owes its inspiration to that on page 320 of the book (Table 21.1).


Vertebrate Life, Pough, Geiser