On the evolution of the mammalian palate

Abstract

In spite of the fact that the possible homologies of the mammalian vomer have been under review for over fifty years, there still remain two strongly conflicting opinions. The original view that the paired “ prevomers” of the reptile fused to form the single vomer of the mammal has been repeatedly attacked, and few writers maintain this homology to-day. Instead, it is usually believed that the mammalian vomer is a derivative of the reptilian parasphenoid, and that the reptilian “ prevomers” are represented in the mammal only by the palatine processes of the premaxillae. But during the last few years doubts have been expressed about the validity of some of the evidence used, and it has been claimed that there is now good reason to return to the original homology. Whether the mammalian vomer evolved from the parasphenoid or from the “ prevomers” is not, in itself, a very important matter. But the current parasphenoidvomer hypothesis is founded mostly on embryology, while the doubts of its validity have arisen from a consideration of recent palaeontological evidence, and the importance of the problem lies in the necessity of finding an explanation which satisfies both lines of evidence. To do this it has been necessary to re-examine both the facts and the lines of reasoning. The value of such an analysis lies in its promise to expose unreliable evidence and misleading methods.