American Museum of Natural History

452 OSBORN, THE REPTILIAN SUBCLASSES DIAPSIDA AND SYNAPSIDA.
late Professor George Baur, who always seemed to me to be nearer the truth
and more logical in his theories than the late Professor Edward D. Cope whose
classifications were based too largely on single characters. The comnprehensive
treatise of Professor Carl von Zittel has been of the greatest service in the study
of the reptiles, as well as the more recent and more condensed treatise of another
friend, Dr. Arthur Smith Woodward. After this memoir had been practically
completed I fortunately learned through Franz Baron Nopcsa of the important
recent papers of Dr. R. Broom, and I received some of these papers from the
author in time to incorporate part- of his--work in the present memoir; especially
that on the homologies of the vomer and prevomer, which tends to confirm rather
than disprove the theory of the division of the Reptilia into subclasses; also
his surprising demonstration -of the actual affinity of Procolophon to the Rhynchocephalia
rather than to the Cotylosauria. I am greatly indebted to Dr. J.
H. McGregor and Mr. W. K. Gregory for assistance in the preparation of
this memoir.
PART I.-THE PRIMARY DIVISION OF THE REPTILIA INTO
TWO SUBCLASSES, SYNAPSIDA AND DIAPSIDA.
The classification and phylogeny of the Reptilia is at present in very great
confusion. It appears that Cope was less logical in his arrangement of the reptilian
orders than in that of any other group of vertebrates: his 'Archosauria' will
have to be abandoned; his 'Theromorpha,' as Baur showed, was founded upon a
misconception and must be totally eliminated from classification. The impression
left by the masterly writings of Baur was that the Reptilia all traced their origin
back through a primitive Sphenodon-like form or 'Proganosaurian,' to the Cotylosauria.
This is certainly an error, because many reptiles never passed through a
'proganosaur' or rhynchocephalian stage.
None the less, Cope and Baur have been, more or less unconsciously, among
the leading contributors toward a movement or tendency which appears to result
in the separation of the Reptilia into two great groups phylogenetically distinct.
The steps in this movement may now be briefly outlined.
I. OUTLINE OF RECENT HISTORY OF CLASSIFICATION.
(i) In I867 there began a tendency to classify the Reptilia by the structure
of the temporal region of the skull. In that year Gunther1 showed that the
RHYNCHOCEPHALIA differ from the Squamata (Lacertilia, Mosasauria, Ophidia) in
the possession of both upper and lower temporal arches, the Squamata retaining
only the upper arch.
' GUnther, A. C. Contribution to the Anatomy of Hat/eria (Rhynchocephalus Owen). Philos. Trans. Roy. Soc.,
London, CLVII, pp. 595-629, I867.