order i EHYXCHOCEPHALIA 145 



effected by Blainville in 1816, and approved by Menem in 1820, but a satis- 

 factory classification was impossible until after the researches of Owen, 

 Huxley, von Meyer, Marsh, Cope, Osborn, Baur, and others had vastly 

 increased our knowledge of fossil forms. Universal agreement does not by 

 any means obtain regarding the limitations of the different groups, but most 

 modern authorities are in favour of recognising nine independent orders, as 

 follows : — Rhynchocephalia, Squamata, Ichthyosauria, Sauropterygia, Theromorpha, 

 Chelonia, Crocodilia, Dinosauria, and Pterosaur in. Of these the Permian 

 Rhynchocephalians include the earliest and most primitive forms, and may 

 be regarded in a broad sense as ancestral to all Archosauria (or reptiles with 

 two temporal arches), as well as Aves. 



Order 1. RHYNCHOCEPHALIA. 1 



Lacertiform reptiles with amphicoelous vertebrae, sometimes pierced for the noto- 

 chord. Upper and lower temporal arcades well defined. Quadrate fixed, ami 

 Imt tressed by the pterygoids, which extend forward to the vomer; premaxillae paired. 

 Mandibular symphysis usually ligamentous; teeth acrodont. Sternum present; 

 sacrum composed of two, or in the Pelycosauria of three vertebrae. Limbs ambu- 

 latory, pentadactyle. Dermal armour of corneous scales. 



The existing genus Sphenodon (Hatteria) of New Zealand is the sole 

 survivor of an ancient and primitive order of reptiles which attained its 

 maximum specialisation in the Trias, and whose earliest representatives 

 (Proterosauria) resemble the Microsaurian Stegocephalia in noteworthy respects. 

 This primitive Permian group also occupies the cleft between Squamata, 

 Crocodilia, and Dinosauria, and is in all probability ancestral to birds through 

 a primitive Dinosaur-avian stem. 



The body in Rhynchocephalians is lizard-like, long-tailed, sometimes scaly ; 

 the vertebral centra are amphicoelous or amphiplatyan, with persistent noto- 

 chord, and often with small intercentra (hypocentra). The neural arches are 

 well ossified, and zygapophyses and diapophyses usually conspicuous. With 

 the exception of the anterior cervicals and posterior caudals, all the vertebrae 

 bear strong single-headed ribs. Several or numerous longitudinal series of 

 abdominal ribs occur between the limb girdles, and correspond to the ventral 

 armouring of Stegocephalians. 



The skull (Fig. 237) is remarkable for the large size of the orbits and 

 temporal vacuities. There are always two temporal arcades, the upper one 



1 Literature : 



Baur, G., Palaeohatteria and the Proganosauria (Amer. Journ. Sci. [3], vol. XXXVII. p. 310), 

 1889. — Boulenger, G. A., On British remains of Homaeosaurus, with remarks on the classification 

 of the Rhynchocephalia (Proc. Zool. Soc. p. 167), 1891. — Credner, H., Ueber Palaeohatteria and 

 Kadaliosaurus (Zeitschr. deutsch. geol. Ges. vol. XL. p. 488), 1888. — Dollo, L., Premiere note sur 

 le Simaedosaurus d'Erquellinnes (Bull. Mus. Roy. d'Hist. Nat. Belg. vol. III.), 1884. — Sur 

 l'identite des genres Champsosaurus et Simaedosaurus (Bull. Soc. Belg. Geol. vol. V. p. 151), 1891. 

 — G anther, A., Contribution of the anatomv of Hatteria (Phil. Trans, vol. CLVIL), 1867. — Huxley, 

 T. H., On Hyperodapedon, etc. (Quar. Journ. Geol. Soc. vols. XV. p. 435 ; XXV. p. 138 ; XLIII. 

 p. 675), 1859-87. — Lortet, L., Les reptiliens fossiles du bassin du Rhone (Arch. Mus. d'Hist. Nat. 

 Lyon, vol. V.), 1892. — Meyer, II. von, Zur Fauna der Vorwelt (vols. III., IV.), 1857-60.- — Seeley, 

 H. G., On Proterosaurus (Phil. Trans, vol. CLXXVIII. p. 187), 1887.— Siebenn yck, F., Zur 

 Osteologie des Hatteria-Kopfes (Sitzber. Akad. Wiss. Wien, vol. CII. pt. 1), 1893. — Wagner, A., 

 Saurier aus dem lithographischen Schiefer (Abhandl. Baver. Akad. Wiss. vols. VI., VII., IX.), 

 1852-61. 



VOL. II L 



