Acta Geologica 3. (1955)
4. szám - Kretzoi, M.: Dolomys and Ondatra
M. KRETZOI As regards the shape of Mj cap and development of M3, Ondatra Link 1795 cannot be distinguished from Dolomys, their palatal structure, too, being almost identical ; divergences appear in two respects only : a) the re-entrant folds of the molars in Ondatra are filled with cement (never occurring in any of the above three genera, not even as an exception) ; b) even the smallest form of the genus Ondatra are much larger in size than those of the undoubted species of Dolomys. However, in view of the fact that cement is lacking in the unworn teeth and that the folds are filled gradually with advancing age only, while the difference in size is not too convincing in the smaller fossil forms (e. g. in the case of Ondatra annectens Brown) ,the delimitation of the said two genera, as based on the known characters, is anything but sharp. This seems to completely justify the hypothesis of MÉHELY regarding the close relationship between the two genera. The rootless teeth of Neofiber True 1884 serve to distinguish it from the rest, while, in other respects, it is quite as difficult to separate it from Dolomys s. str. as from Ondatra. * The above survey has offered not only a more detailed arrangement of the forms known as Dolomys but has, at the same time, demonstrated that the three above treated genera (and especially one of them, viz. Dolomys s. str.) are in the closest relation to the Ondatra types of North America. This close relation makes it necessary to separate them from the other groups so that they should be included in the family of voles as a separate unit. This, however, is not so easy, one of the chief difficulties being that, with complete disregard of phylogenetic principles, the supergeneric system of the voles still follows the conservative tripartition -— lemmings, voles, Ellobius — although this division has become obsolete from ethiological-external morphologic points of view. The evolution of the voles (Arvicolidae Gray 1821 = Microtidae Cope 1891) from Hesperomyne ancestors has supposedly taken place since the beginning of the Miocene age ; in the course of this evolution a prismatisation of the molars, as a consequence of Graminea food, has been brought about in a manner perfectly identical to that observed in the phyletic evolution of horses. While the Miocene representatives of this ancestral line have not been found or recognized yet, its lowest Pliocene and late lower Pleistocene (Sicilian) members are represented by the East Asiatic genera Anatolomys and Microtodon and the South Hungarian genus Baranomys. This branch, i. e. the Baranomyinae is sharply distinguished from the Mongolian Lower Pleistocene Microtoscoptes. Not far beyond the line of Microtoscoptes, the branch of Ellobiinae has branched off ; small-sized relatives of this branch appear in the Lower Sicilian of Germany and Hungary as the genera Germanomys and Ungaromys ; suppos-