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ORDERS OF CLASS

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Originally appearing in Volume V23, Page 145 of the 1911 Encyclopedia Britannica.
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ORDERS OF CLASS REPTILIA 1. Anomodontia.—Bones of postero-lateral region of skull forming a complete roof over the temporal and masseter muscles, or contracted into a single broad zygomatic arch, leaving a superior-temporal vacuity. Pineal foramen present. Ribs completely or imperfectly double-headed. No abdominal ribs. A large separately ossified epicoracoid. Limbs for support as well as progression; third and fourth digits with not more than three phalanges. Dermal armour feeble or absent. Range.—Permian and Triassic. 2. Chelonia.—Postero-lateral region of skull as in Anomodontia, except bones of ear-capsule more modified. No pineal foramen. Ribs single-headed. No sternum. Pectoral and pelvic arches unique in being situated completely inside the ribs. No epicoracoid. Abdominal ribs replaced by three or four pairs of large plates, which, with the clavicles and interclavicle, form a plastron. Limbs only for progression; third and fourth digits with not more than three phalanges. A regular dorsal carapace of bony plates intimately connected with the neural spines, and ribs of seven to nine dorsal vertebrae. Range.—Upper Triassic.to Recent. 3. Sauropterygia.—Bones of postero-lateral region of skull contracted into a single broad zygomatic arch, leaving a superior-temporal vacuity. Pineal foramen present. No fused sacral vertebrae. All dorsal ribs single-headed, articulating with transverse processes of the neural arches. Abdominal ribs forming dense plastron. Apparently no sternum. Coracoid, pubis and ischium in form of much-expanded plates. Limbs modified as paddles, with not more than five digits, of which the third and fourth always have more than three phalanges; all digits usually consisting of numerous phalanges. No dermal armour. Range.—Upper Triassic to Cretaceous. 4. Ichthyopterygia.—Bones of postero-lateral region of skull contracted into a single broad zygomatic arch, leaving a superior-temporal vacuity. Pineal foramen present. Vertebral centra short and deeply biconcave, with feeble neural arches which are almost or completely destitute of zygapophyses. No fused sacral vertebrae. Cervical and dorsal ribs double-headed, articulating with tubercles on the vertebral centra. Abdominal ribs forming dense plastron. Apparently no sternum. Coracoid an expanded plate, probably with cartilaginous epicoracoid. Pelvis very small, not connected with vertebrae. Limbs modified as paddles, with digits of very numerous short phalanges, which are closely pressed together, sometimes with supplementary rows of similar ossicles. No dermal armour. A vertical triangular caudal fin, not supported by skeletal rays. Range.—Triassic to Cretaceous. 5. Rhynchocephalia.—Bones of postero-lateral region of skull contracted into two slender zygomatic bars, leaving a superior-temporal and a lateral-temporal vacuity, and partly exposing the quadrate bone from the side. Pineal foramen present o absent. Ribs single-headed. Abdominal ribs present. Sternum present. Epicoracoid cartilaginous. Limbs only for progression; third and fourth digits with four or five phalanges. Dermal armour feeble or absent. Range.—Lower Permian to Recent. 6. Dinosauria.—Postero-lateral region of skull as in Rhynchocephalia. No pineal foramen. Cervical and dorsal ribs double-headed. Rarely abdominal ribs. Sternum present, but apparently no clavicular arch. Limbs for support as well as progression; third and fourth digits with four and five phalanges respectively. Dermal armour variable. Range.—Triassic to Cretaceous. 7. Crocodilia.—Postero-lateral region of skull as in Rhynchocephalia. No pineal foramen. Cervical and dorsal ribs double-headed. Abdominal ribs present. Sternum present; also inter-clavicle, but no clavicles. Limbs only for progression on land or swimming; third and fourth digits with four or five phalanges. Dermal armour variable. Range.—Lower Jurassic to Recent. 8. Ornithosauria.—All bones extremely dense, light and hollow, the organism being adapted for flight. Postero-lateral region of skull as in Rhynchocephalia. No pineal foramen. Cervical and dorsal ribs double-headed. Abdominal ribs present. Sternum present, and keeled for attachment of pectoral muscles; no clavicular arch. Fifth digit of hand much elongated to support a wing-membrane, but with only four phalanges. Hind limb feeble. No dermal armour. Range.—Lower Jurassic to Cretaceous. i IICI,I, i I I~ ~~~ i lhll I~ r zr plupl II III mll~1lN ~~4i14~1, qu 4u Lcu. j A B After Credner. After C. W. Andrews. B, Palate of Mesozoic Reptile (Plesiosaurus macrocephalus). b.occ, basioccipital; bs, basisphenoid; eept, ectopterygoid; i.pt, interpterygoid vacuity; j, jugal; mx, maxilla; pas, parasphenoid; pl, palatine; pmx, premaxilla; pt, pterygoid; pt. par, posterior pares; qu, quadrate; s.o, suborbital vacuity; v, vomer. pax.. mac ,.pt.nar pt. ncsr... S. o. 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. Order I. ANOMODONTIA.—The Anomodonts are so named in allusion to the peculiar and unique dentition of the first-discovered genera. They are precisely intermediate between theand 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 Therio- B. ~~V... im" s: "~m~ptt+t ~I~III!lI1~11~NI Illl~uoL 7J- F qu. From A. S. Woodward, Outlines of Vertebrate Palaeontology. fr, frontal; j, jugal; 1, 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. sq. 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 dontia 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 Wurttemberg, where a complete " shell" has been found (Proganochelys). Its members are proved to have been toothless since the Jurassic period, and have only changed very From A. S. Woodwartl, Outlines of Vertebrate Palaeontology. d, dentary; j, jugal; l.t.f, incipient lateral temporal vacuity; la, lachrymal; nix, maxilla; na, nasal; orb, orbit; pa, parietal; pmx, premaxilla; prf, prefrontal; pia., postorbital; ptf, post-frontal; s.t, supratemporal (prosquamosal); sq, squamosal. slightly since their first appearance. The marine turtles seem to have first: acquired elongated paddles and vacuities in the shell during the Cretaceous period, and the Trionychia, destitute of epidermal shields, apparently arose at the same time. Order 3. SAUROPTERYGIA.—These are amphibious or aquatic reptiles (fig. 4). The head is comparatively small in most genera, and the neck is usually elongated though not flexible. The tail is insignificant, generally short, and both pairs of paddles seem to have been concerned in progression. The order appears to have arisen from a group of land-reptiles, for its earliest members, from the Triassic of Europe (Lariosaurus) and from the Permo-Carboniferous of S. Africa (Mesosaurus) and Brazil (Stereosternum), are all amphibious animals. They are comparatively small, and their limbs are only just becoming paddle-like. The skull suggests affinities with the terrestrial effective paddles with elongated digits, and as the genera are traced upwards in the geological formations it is possible to observe how the arches supporting the limbs become more rigid until the maximum of strength is reached. A few genera, such as Pliosaurus from the Jurassic and Polyptychodon from the Cretaceous of Europe, are distinguished by their relatively large head and stout neck. Some of the largest Upper Jurassic and Cretaceous species must have been so metres in length. They were cosmopolitan in their distribution, but became extinct before the dawn of the Tertiary period. Order 4. ICHTHYOPTERYGIA.—The Ichthyosaurians are all fish-shaped, with a relatively large head and very short neck. Both pairs of paddles are retained, but the hinder pair is usually. very small, and locomotion seems to have been chiefly effected by a large caudal fin. This fin, as shown in impression by certain fossils from Wurttemberg and Bavaria, is a vertical, triangular, dermal expansion, without any skeletal support except the hindermost part of the attenuated vertebral column, which extends along the border of its lower lobe (fig. 5). Another triangular fin, without skeletal support, is known to occur on the back, at least in one species (fig. 5). Some of the genera are proved to have been viviparous. Like the Sauropterygia, the Ichthyopterygia appear to have originated from terrestrial ancestors, for their earliest Triassic representatives (Mixosaurus) have the teeth less uniform and the limbs slightly less paddle-. shaped than the latter genera. In this connexion it is noteworthy that their hollow conical teeth exhibit curious infoldings of the wall, like those observed in many Labyrintho.donts, while their short, biconcave vertebrae almost exactly resemble those of the Labyrinthodont Mastodonsaurus and its allies. As the Ichthyosaurs are traced up-wards in geological time, some genera become almost, or quite, toothless, while the paddles grow wider, and are rendered more flexible by the persistence of . cartilage round their constituent bones (Ophthalmosaurus). They were cosmopolitan in distribution, but disappeared from all seas at the close of the Cretaceous period. The largest forms, with a skull 2 metres in length, occur in the Lower Lias. Order 5. RHYNCHOCEPHALIA.—TheSe are small lizard-shaped reptiles, which have scarcely changed since the Triassic period. Though now represented only by Sphenodon or Hatteria, which survives in certain islands off New Zealand, in the Mesozoic epoch they ranged at least over Europe, Asia.and North America. They comprise the earliest known reptile, Palaeohatteria, from the Lower Permian of Saxony, which differs from the Triassic and later genera in having an imperfectly ossified pubis and ischium, more numerous abdominal ribs, and the fifth metatarsal Lias, Wurttemberg. (After E. Fraas.) The irregularities behind the triangular dorsal fin are torn pieces of skin, Anomodontia, and the shape of the scapula seems to show some connexion with the Chelonia. The truly aquatic Sauropterygians of the Jurassic (fig. 4) and Cretaceous periods possess most bone normal. They are also represented in the Permian, chiefly of North America, by the so-called Pelycosauria, which have sharp teeth in sockets, and are remarkable for the extreme
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