Primitive Reptiles. a Review

PRIMITIVE REPTILES A REVIEW S. W. WILLISTON From the Paleontological Laboratory, University 01 Chicago ONE FIGURE The evidence seems now conclusive that th.e extensive Ameri- can reptilian fauna hitherto called Permian is in part of upper Pennsylvanian, in part of lower Permian age, and, therefore, is the oldest known. From other parts of the world there are only a few known forms supposed to be of equivalent, or approxi- mately equivalent, age, the chief of which, if not the only ones, are Stereosternum and Mesosaurus from the Santa Catherina System of Brazil, the latter genus also from the upper Dwyka of South Africa. From immediately superjacent beds in South Africa, doubtless of lower Permian age, but one or two reptiles are known, Archaeosuchus and Eccasaurus, referred by Broom, the former at least, to the dinocephalian group of the Therapsida. From the Beaufort beds, upper and lower, of Africa, numerous genera of reptiles are known, referred to the Cotylosauria and Therapsida. Because of the close affinity or identity of some of'these genera with those found in Russia, they doubtless should all be considered of upper Permian age, as distinguished from lower Permian. From the Rothliegende of Germany and France, of lower Permian age, the following genera of reptiles are known: Stephanospondylus, Phanerosaurus, Datheosaurus, Stereorhachis, Kadaliosaurus, Callibrachion, Aphelosaurus, and Paleohatteria (Haptodus). Leaving Archaeosuchus and Eccasaurus out of account in the following discussion, the present paper will deal with the carboniferous and lower Permian reptiles only, including 637 638 S. W. WILLISTON the genera mentioned above and the numerous ones known from the American Permio-carboniferous. Two other, disputed groups of contemporary air-breathers, believed to be reptiles by some authors of repute, will be discussed in the sequel. All of the so-called orders represented by these reptiles are believed to be continuous, not only throughout the Permian of Europe or Africa, but also throughout more or less of the trias if not the mesozoic, though in most cases the later forms are either distinctly modified, or have reached a higher degree of specialization; and their discussion may be omitted here. Pareia- saurus and Propappus, for instance, from the upper Permian of Russia and Africa, have dorsal osseous scutes, a distinct acromi- a1 process of the scapula, and coossified calcaneum and astragalus, all unknown in the American Cotylosauria; characters, which in themselves are sufficient to separate the Pareiasauria as a distinct group. Procolophon, also, with its allies Telerpeton, Sclerosaurus and Koiloskiosaurus from the trias, have departed so far from the primitive simplicity of the earlier types of America in the skull structure and in the pectoral girdle as stated by Huene, that they may well be separated into a group by themselves. Procolophon has been supposed for years, to be a primitive form of the double-arched or ‘Diapsidan’ type, notwith- standing its occurence in much later deposits than those of Paleo- hatteria. Huene has recently expressed the opinion, one I have had for the past five years, that the Procolophonia have nothing to do genetically with the rhynchocephalian or archaeosaurian phylum. Using then the term Permocarboniferous to include the upper carboniferous and lower Permian, and omitting the imperfectly known Archaeosuchus and Eccasaurus, we have perhaps thirty or more genera of undisputed reptiles which it will be of interest to compare directly. The first and lowest group of these, the Cotylosauria as usually accepted, began in the upper Pennsylvanian of North America and continued into the Procolophonia of the trias of South Africa and Europe; it has generally been believed to be the order from which all later Amniota have been derived. The second order, PRLMITIVE REPTILES 639 the Theromorpha of Cope as limited by me,' in part the Pely- cosauria of authors, began also in carboniferous times and extend- ed as an order into triassic times in Europe. The third group, the Proterosauria, as represented by Paleohatteria, Proterosaurus and less well known allied forms, began, so far as we know, in the middle Rothliegende of Germany and continued throughout the Permian; it is generally supposed to be the ancestral group from which all later true reptiles, that is the double-arched forms, arose, and is often included among the Rhynchocephalia, sens. lat. The fourth group, the Proganosauria, as originally defined by Baur and later restricted by Osborn and McGregor, has been accepted by some, though not by all students as an early group of the Sauropterygia, which continued to near the close of mesozoic times. From a study of all these I have endeavored to summarize and correlate those structural characters upon which phylogenies and classificabion must depend. Many of the known forms are as yet represented by fragmentary and incomplete specimens only, whether those of America or of other lands; of the latter I have little or no autoptic knowledge, a fact less to beregretted since most of them, and those the most important ones, have been described and illustrated by competent students. Of the American forms I have studied with more or less care nearly all the known material, with the exception of that preserved in the museum at Munich, which has been ably discussed by Broili. Of this material I am familiar with complete or nearly complete skeletons pertaining to the following genera: Diadectes Cope, Diasparactus Case, Limnoscelis Will., Seymouria Broili, Cap- torhinus Cope, Labidosaurus Cope, Varanosaurus Broili, Casea Will,, Ophiacodon Marsh and Dimetrodon Cope. I have also studied the less complete specimens belonging in the following genera : Diadectoides Case, Pantylus Cope, Edaphosaurus (Naosaurus) Cope,2 Sphenacodon Marsh, Clepsy drops Cope, Araeoscelis Williston and Animasaurus C. and W,, together with the more fragmentary material of nearly all the other known gen- 1 American Permian Vertebrates, p. 70. 2 The identity of Naosaurus with Edaphosaurus is now established. 640 S. W-. WILLISTON era from Illinois, Kansas, Oklahoma, Texas, New Mexico and Colorado. And I need not add that I have diligently studied all the literature bearing on these American reptiles, especially that of Case and Broili. I am indebted to Dr. Case for the kindly criticism of the manuscript of the present article. It will be understood that I give the characters so far as they seem to be established by numerous forms, though it is quite possible that future discoveries of new forms, or of better material of forms now imperfectly known, may require the removal of some of the characters included under the constant list to the inconstant or variable list. But the converse will not be possible unless I have committed errors, since here the evidence is positive, not negative. Among so many and- diverse forms it must be evident that most of the characters common to all, so far as the material goes, are to be considered as primitive ones, that is, characters possessed by the earlier or earliest reptiles far back in Pennsylvania times. But, by no means are these the only primitive characters, since it is very evident that even by the close of the carboniferous not a few had become variable. CONSTANT CHARACTERS OF PERMOCARBONIFEROUS REPTILES Crawling reptiles from about 0.3 to about 24 meters in length. A parietal foramen, postorbital, postfrontal, lacrimal, nasal and probably at least one additional membranous cranial bone not occurring in Sphenodon present in the skull. Quadratojugal, paroccipital, epipterygoid and septomaxillary probably always distinct; parietals, frontals and nasals never fused in middle line; stapes probably always large; a separate prearticulae bone; splenial entering symphysis ; coronoid small; teeth on paired premaxillae, maxillae, palatines, pterygoids and dentaries; pterygoids articulating with vomers (prevomers), basisphenoid, palatines and quadrates; quadrate always fixed, though not always firmly attached. * This term (1903) had become established in paleontological literature before Gaupp (‘OS), in ignorance of its use, proposed the name goniale for the same bone. PRIMITIVE REPTILES 641 Vertebrae notochordal (or at least deeply and conically bicon- cave) ; all vertebrae to the second-sixth caudal with intercentra and all to the eighth or ninth with ribs, those of the lumbar, sacral and basal caudal united more or less suturally with body and arch, but in all cases the capitulum more or less intercentral in position. Capitulum of free ribs articulating intercentrally, resting more or less on the front end of the centrum, but not articulating with a parapophysial process. Chevrons present on all the caudals, save the first two-six and the extreme terminal ones. Proatlas probably always present. Atlas composed of a large free odontoid supporting the paired neural arch chiefly, and an intercentrum not much larger than the one following Fig. 1 Proatlas, atlas and axis of Ophiacodon between atlas and axis. Axis with anterior zygapophysial facets for articulation with atlas. Interclavicle with expanded anterior part and a long posterior stem; clavicles large, smooth, articulating with interclavicle, scapula and sometimes with the cleithrum; scapula and coracoid suturally united, fused in maturity; anterior coracoid, the so- called procoracoid (the true coracoid of later reptiles) always forming a part of the glenoid articulating surface; a supracoracoid and a supraglenoid foramen always

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