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ORDO 2

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Originally appearing in Volume V23, Page 141 of the 1911 Encyclopedia Britannica.
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ORDO 2. CROCODILIA. This classification received the addition of a fifth Reptilian order which with many Lacertilian characters combined important Crocodilian affinities, and in certain other respects differed from both, viz. the New Zealand Hatteria, which by its first describers had been placed to the Agamoid Lizards. A. GUNTHER,4 who pointed out the characteristics of this reptile, considered it to be co-ordinate with the other four orders of reptiles, and characterizes it thus: Rhynchocephalia.—Quadrate bone suturally and immovably united with the skull and pterygoid; columella present. Rami of the mandible united as in Lacertilians. Temporal region with two horizontal bars. Vertebrae amphicoelian. Copulatory organs, none. 5. Period of the Recognition of a Class of Reptilia as Part of the Sauropsida.—Although so far the discovery of every new morphological and developmental fact had prepared naturalists for a class separation of Reptiles and Batrachians, it was left to T. H. Huxley to demonstrate, not merely that the weight of facts demanded such a class separation, but that the reptiles hold the same relation to birds as the fishes to Batrachians. In his Hunterian Lectures (1863) he divided the vertebrates into Mammals, Sauroids and Ichthyoids, subsequently substituting for the last two the terms Sauropsida and Ichthyopsida.5 The Sauropsida contain the two classes of birds and reptiles, the Ichthyopsida those of Batrachians and fishes. 6. Period of the Consideration of Skeletons of Extinct Reptiles. SIR R. OwEN, while fully appreciating the value of the osteological characters on which Huxley based his division, yet Owen. admitted into his consideration those taken from the organs of circulation and respiration, and reverted to Latreille's division of warm- and cold-blooded (haematothermal and haematocryal) vertebrates, thus approximating the Batrachians to reptiles, and separating them from birds.6 The reptiles (or Monopnoa, Leuck.) thus form the highest of the five subclasses into which, after several previous classifications, Owen 7 finally divided the Haematocrya. His division of this subclass, however, into nine orders, makes a considerable step in the progress of herpetology, since it takes into consideration for the first time the many extinct groups whose skeletons are found fossil. He shows that the number of living reptilian types bears but a small proportion to that of extinct forms, and therefore that a systematic arrangement of the entire class must be based chiefly upon osteological characters. Ilis nine orders are the following: a. ICHTHYOPTERYGIA (extinct)—Ichthyosaurus. b. SAUROPTERYGIA (extinct)—Plesiosaurus, Pliosaurus, Nothosaurus, Placodus. c. ANOMODONTIA (extinct)—Dicynodon, Rhynchosaurus, Oudenodon. d. CHELONIA. e. LACERTILIA (with the extinct Mosasaurus). f. OPHIDIA. g. CROCODILIA (with the extinct Teleosaurus and Streptospondylus). h. DINOSAURIA (extinct)—Iguanodon, Scelidosaurus and Megalosaurus. i. PTEROSAURIA (extinct)—Dimorphodon, Rhamphorhynchus and Pterodactylus. Owen was followed by Huxley and E. D. Cope, who, however, restricted still more the selection of classificatory characters by relying for the purposes of arrangement on a few parts of the 4 " Contribution to the Anatomy of Hatteria (Rhynchocephalus, Owen)," in Phil. Trans. (1867), part ii. 5 An Introduction to the Classification of Animals (London, 1869, 8vo), pp. 104 seq. 5 Anatomy of Vertebrates (London, 1866, 8vo), vol. i. p. 6. 7 Op. cit. p. 16.
End of Article: ORDO 2
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