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Show 204 DR. 0. J. FORSYTH MAJOR ON MIOCENE SQUIRRELS. [Feb. 28, considered by Schlosser himself to be a Lemurid1, and Osborn2 had placed both of them amongst the Pseudolemuriche. Whilst fully agreeing with Schlosser in his main conclusions, for reasons^ which I shall discuss elsewhere, I am again at a loss to see what trituberculism has to do with the matter 3, and would put but one question : H o w comes it that both Protoadapis and Plesiadapis, which are indeed the most ancient types of Rodents hitherto known, show the so-called heel of inferior molars in such a perfect condition4 in spite of trituberculism, which considers these parts as a late addition to the original triangle of inferior molars ? I have declared myself opposed to the tritubercular theory, but have limited my remarks hitherto merely to criticism, though occasionally I offered some positive argument in favour of an hypothesis which is in many points the very reverse of the prevailing theory. It remains now for m e to justify the position I have taken with regard to it; what I am going to say is partly a summing up of preceding remarks, and partly embraces a far wider field, and will, 1 have no doubt, meet with some opposition. N o better starting-point could be chosen than the " Seiuridce," amongst which we meet with the most primitive form of molars of this low order of Mammalia. P The adherents of trituberculism assert that they have proved the Mammalian molar to be traced back to a more and more simple form. I have tried to show that they have failed to do so, and in my turn assert that the molar of Placentalia can be traced to a polybunous form, and that the real tritubercular pattern is a more specialized secondary stage. So that, as a matter of course, the cardinal point to be established is to show, that the more complex forms, which in the Lower Eocene as well as in the recent period are found side by side with the simpler forms, trituberculate or otherwise, are indeed the primitive, the more generalized type. To prove m y assertion, I start from five assumptions :- 1. Brachydonty is the more primitive, the more generalized, condition of molar form, and so is 2. Bunodonty, as opposed to Lophodonty (or Zygodontg, which is the same thing). S. The more brachydont a molar is, the more multitubercidar it is, or, let vs say, polybunous. 4. The transformation, viz., the reduction and simplification, 1 M. Schlosser, " Die Affen, Lemuren, Chiropteren, Insectivoren etc des euro-paischen Tertiars, etc" Pt. I. Wien, 1887, p. 47. 2 Henry Fairfield Osborn, " A Review of the Cernaysian Mammalia " (Proc. Phil. Acad. Nat. Sci., M a y 6th, 1890, pp. 55, 56). 3 " Dass aber dieser Typus (i. e. Trituberculaitypus) auch den Ausgangspunkt fur die oberen Molaren der Nager darstellt, ersehen wir daraus, dass er sich bei Sciurus sogar noch bis in die Gegenwart ziemlich rein erhalten hat." (L. c. p. 240.) 4 Lemoine, I, c. pi. x. |
