9. Squamata.—Bones of postero-lateral region of skull much
reduced and partly absent, never forming more than a slender
superior-temporal bar, thus completely exposing the quadrate,
which is only loosely attached to the cranium at its upper end.
Pineal foramen present. Ribs single-headed. No abdominal ribs.
Sternum present when there are limbs. Limbs, when present, only
for progression; third and fourth digits at least with more than
three phalanges. Dermal armour feeble or absent. Range.—Cretaceous
to Recent.
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| From A. S. Woodward, Outlines of Vertebrate Palaeontology. |
|
Fig. 2.—Diagram of the Cranial Roof in a Labyrinthodont Amphibian, various types of Reptiles, and a Bird. A, Labyrinthodont Amphibian (Mastodonsaurus giganteus). B, Generalized Anomodont or Sauropterygian, passing with slight modification into the Chelonian (sutures dotted to denote inconstancy in fusion of elements). C, Ichthyosaurus. D, Generalized Rhynchocephalian, Dinosaurian, Crocodilian, or Ornithosaurian. E, Generalized Lacertilian, often losing even the arcade here indicated. F, Generalized Bird. fr, frontal; j, jugal; l, lateral temporal vacuity; la, lachrymal; mx, maxilla; n, narial opening; na, nasal; o, orbit; pa, parietal; pmx, premaxilla; prf, prefrontal; ptf, postfrontal; pto, postorbital; q.j, quadrato-jugal; qu, quadrate; s, supratemporal vacuity; s.t, supratemporals and prosquamosal; sq, squamosal. Vacuities shaded with vertical lines, cartilage bones dotted. |
Order 1. Anomodontia.—The Anomodonts are so named in allusion to the peculiar and unique dentition of the first-discovered genera. They are precisely intermediate between the Labyrinthodont Batrachia and the lowest or Monotreme Mammalia. They flourished at the period when the former are known to have reached their culmination, and when the latter almost certainly began to appear. Many of them would, indeed, be regarded as primitive Mammalia, if they did not retain a pineal foramen, a free quadrate bone, and a complex mandible. The term Theromorpha or Theromora is thus sometimes applied to the order they represent. So far as known, they are all land-reptiles, with limbs adapted for habitual support of the body, and their feet are essentially identical with those of primitive mammals. Most of them are small, and none attain a gigantic size. They first appear in the Permian of Europe and North America, and also occur in the Triassic both of Europe and India, but they are best represented in the Karoo formation (Permian and Triassic) of South Africa. The Pariasauria most closely resemble the Labyrinthodont Amphibia, but have a single occipital condyle. Pariasauria itself is a massive herbivorous reptile, with a short tail, and the limbs adapted for excavating in the ground. It is known by several nearly complete skeletons, about 3 metres in length, from South Africa and northern Russia. Elginia, found in the Elgin sandstones of Morayshire, Scotland, is provided with horn-like bony bosses on the skull. Another apparently allied genus (Otocoelus) has a carapace suggesting that it may be an ancestral Chelonian. The Theriodontia exhibit the marginal teeth differentiated (in shape) into incisors, canines and molars (fig. 3). They have two occipital condyles, as in mammals. They seem to have been all carnivorous, or at least insectivorous, but the malariform teeth vary much in shape in the different genera. Cynognathus (fig. 3) and Lycosaurus have cutting teeth, while Tritylodon and Gomphognathus possess powerful grinders. The Dicynodontia have one pair of upper tusks or are toothless: their occipital condyle is trefoil-shaped, as in Chelonia. Dicynodon itself occurs in the Karoo formation of S. Africa, while other genera are represented in India, N. Russia and Scotland.
Order 2. Chelonia.—This order occurs first in the Upper Triassic of Württemberg, where a complete “shell” has been
