p. 531-533 : ill. ; 24 cm.Includes bibliographical references (p. 533)

Case, E. C. (Ermine Cowles), b. 1871.

American Museum of Natural History Scientific Publications

56.79,5L(1 15)Article XXVI.-NOTES ON THE SKULL OF LYSOROPHUSTRICARINA TUS COPE.BY E. C. CASE.The genus Lysorophus was first described by Cope from several verte-brae from the bone bed of eastern Illinois (Cope, '77). Later Case gave amore detailed account of the vertebral column (Case, '00 and '02). FinallyBroili, from very full material, supplemented the description of the verte-brie and gave an account of the skull. He came to the conclusion thatLysorophus was entirely limbless and a member of an extremely primitivefamily of reptiles to which he gave the name Paterosauridee (Broili, '04and '04). This family he regarded as one of the original groups of reptiles,assigning to the reptiles a diphyletic origin. He says ('04): "Wir mussenalso fur die Reptilien eine diphyletische Entwicklung annehmen, dereneine Wurzel bei den amphibischen Stegocephalen zu finden, deren andere,aller Wahrscheinlichkeit nach, bei den Fischen zu suchen ist."A series of five skulls in the collection of the American Museum, collectedby the author in Texas in the summer of 1906, permits some addition toBroili's description of the skull. In one the palate is exposed and a carefulpreparation has revealed something of the interorbital structure. Thebones of the upper surface show a practical agreement with the descriptiongiven by Broili. The bone described by him as the postfrontal extendsforward to the nostril and forms a portion of its border, it having the positionusually occupied in the reptiles by the postfrontal, prefrontal and the lachry-mal. The posterior angles of the skull and the region of the nostrils arewider than figured by Broili, but these may well be specific differences(Fig. 1, C).The palate is distinctly amphibian. The posterior surface is formed bya large flat bone, undoubtedly a parasphenoid; in two specimens whichshow this bone there is a line dividing it into anterior and posterior portions,but it is impossible to say whether this is a simple break or a break followingthe line of a suture. In one specimen the posterior portion is directly con-tinued into the occipital region forming a portion of the articulation; it isimpossible to tell whether this occipital portion is a separate element or iscontinuous with the large plate. I take the large plate to be the para-sphenoid plus the basisphenoid, with the basioccipital cartilaginous. Itseems certain that Broili's assumption, that there was a basioccipital with- ~~~~~~~5.31Bulletin American Museum of Natural History. [Vol. XXIV,a single, reptilian condyle and that it has been lost, is wrong. The articu-lation of the skull to the vertebral column was by two exoccipital (?) condyles.Anterior to the parasphenoid it is impossible to determine the separateelements. There are two nearly concentric rows of sharp, even teeth. Themaxillary-premaxillary series is nearly semicircular and extends back nearlyas far as the anterior end of the parasphenoid. The inner, vomerine seriesis shorter but has nearly the same form as the outer. Between the innerrows of teeth and the plates which support them there is a deep vacuityextending to the upper surface of the skull; this region was excavated withthe greatest care and not the slightest trace of any roof to this portion of theFig. 1. Lysorophws tricarinatus Cope. Figures X 2. A, lateralview of skull; B, posterior view of skull; C, upper view of skull; D,palatal view of skull.mouth was encountered. It probably represents the large posterior openingsof the nares (Fig. 1, D).The lateral view of the skull shows the large orbital cavity. Broiliconsiders that this must have been divided by a slender bar into temporaland orbital cavities, but in several perfect specimens of this region I find notrace of such a bar. The interorbital septum is composed, in the specimen,of three pieces but these may be fractured portions of an originally solidplate. In the posterior portion of the cavity a vertical plate appears justbeneath the anterior edge of the quadrate; this may be the epipterygoid orthe anterior edge of the brain case, more probably the latter (Fig. 1, A).The articulation with the vertebral column was by two condyles formed532Case, Skull of Lysorophus tricarinatus Cope.by distinct, exoccipital elements (Fig. 1, B). In two specimens there arepaired pre-atlantal elements between the skull and the first vertebra.The evidence furnished by the palate emphasizes the extremely primitivecharacter, as determined by Broili. The complete ossification of the verte-br.e, the intra-vertebral position of the ribs (some of which are distinctlytwo-headed), and the well developed quadrate speak for the reptilian char-acter of the animal; but the presence of the parasphenoid and the doublearticular condyles seem to render its amphibian nature unquestionable.Were it not for the extreme specialization of this limbless, Gymnophiona-like form it would occupy almost exactly the transitional position betweenthe amphibians and reptiles. This evidence of its amphibian naturenegatives the conclusion of Broili, drawn from the presence of jugularplates, that the reptiles may have had a diphyletic origin and have sprungfrom the fish as well as from the amphibians.1877. Cope, E. D. Descriptions of the Extinct Vertebrata from the Permian andTriassic formations of the United States. Proc. Am. Phil. Soc., Vol.XVII, pp. 182-193.1900. Case, E. C. The Vertebrates from the bone bed of Vermillion County, Ill.Journ. Geol., Vol. VII, p. 698.1902. Case, E. C. Paleontological Notes. Journ. Geol., Vol. X, No. 3, p. 256.1904. Broili, Ferd. Permische Stegocephalen u. Reptilien aus-Texas. Paleonto-graphicca, Bd. L, p. 1.1904. Broili, Ferd. Stammreptilien. Anat. Anzeiger, Bd. XXV, p. 579.1908.] 533

Skull of Lysorophus tricarinatus Cope

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