Beginning of the age of mammals in Asia : the late Paleocene Gashato fauna, Mongolia. Bulletin of the AMNH ; v. 144, article 4

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New York : [American Museum of Natural History]
"The earliest Tertiary mammalian fauna known from Asia occurs in southern Mongolia, where it is found in late Paleocene sediments approximately 55 million years old exposed at Gashato and in the Nemegt Basin. Romer (1966) has proposed, but not defined, a 'Gashatan Asiatic Age' for the Gashato fauna and we propose that the term be extended to the occurrence of the same fauna, although to a different faunal facies, in the Nemegt Basin, subsuming Romer's (1966) 'Ulanbulakian Asiatic Age.' We supply a definition of the 'Gashatan Asiatic Age': the joint overlapping time ranges of Palaeostylops, Pseudictops, Prionessus, and Eurymylus. Additional localities in Sinkiang and Kwangtung may also be Gashatan in age. The Gashato fauna is made up of a mixture of endemic genera and a few genera that evidently reached Asia via the Bering route from North America and beyond. There is no special similarity to Paleocene faunas of Europe, but this could be because of a double filtering action. Gashatan mammals have been the notoungulates, but recently Paleocene notoungulates been found in North America and there is no evidence that notoungulates as such originated in Asia. At the beginning of the Eocene (Sparnacian), increased northern dispersal brought about extensive, but still not complete, faunal replacement in eastern Asia. Analysis of geophysical data, as well as the faunal data, suggests that there is strong evidence for a dry-land dispersal route between the North American and European crustal blocks via Greenland and the Barents shelf as late as Sparnacian time in the Eocene, but not thereafter. During Paleocene time, climate and other factors had a filtering effect on dispersal via both the Bering and Greenland-Barents shelf routes, but the former was closer to the rotational pole position in the Paleocene and was a more effective filter. During Sparnacian time, the Bering area still acted as a filter, but the Greenland-Barents shelf route now showed little filter action. Presumably this was the result of a more equable climate. There is no evidence for a Greenland-Iceland-Faeroes dispersal route and some evidence against it. No attempt is made in the present paper to reevaluate, except insofar as they bear on correlation, the Gashatan multituberculates, pseudictopids, eurymylids, Phenacolophus, or pantodonts, but the following taxonomic adjustments are made: 1. Opisthopsalis is synonymized with Sarcodon, and Sarcodon and Hyracolestes are added to the insectivoran family Deltatheridiidae. 2. A new order, Anagalida, is proposed. The Anagalida includes the families Zalambdalestidae, Pseudictopidae, Anagalidae, and Eurymylidae. The Anagalidae are somewhat lagomorph-like and are believed to be related to lagomorphs. 3. Praolestes is referred to the Zalambdalestidae. 4. The Cretaceous genus Zalambdalestes is known from a single species, Z. lechei. The type specimen of Z. lechei is an extremely aged individual with cheek-tooth crowns nearly worn away. P[superscript]1 and P[superscript]2 have dropped out and the alveoli have closed. The type specimen of 'Z. grangeri' is a somewhat younger individual of the same species and the referred specimens in the Polish collections are younger still. New illustrations of American Museum specimens of Zalambdalestes are provided. 5. The Anagalidae are reported from the Paleocene for the first time and a new genus and species, Khashanagale zofiae, is named. A second species of Khashanagale or of a closely related form is present at Gashato, but is not named. 6. A small Dissacus-like mesonychid is present in the Gashato fauna at Gashato. 7. In the classification of uintatheres, utilization of Flerov's subfamily Prodinoceratinae is advocated in preference to Wheeler's subfamily Bathyopsinae"--P. 313.
p. 271-317 : ill., maps ; 27 cm.
Includes bibliographical references (p. 314-317).