A new Eocene cylindrodont rodent (Mammalia, Rodentia) from the eastern Gobi of Mongolia. American Museum novitates ; no. 3253

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New York, NY : American Museum of Natural History
A new genus and species of cylindrodont rodents, Proardynomys borkhoii, from the middle Eocene Mergen locality of the eastern Gobi, Mongolia, is among the earliest cylindrodontids of Asia. Comparisons with cylindrodontids, sciurids, aplodontids, ischyromyids, and ctenodactyloids show that P. borkhoii is most similar to Ardynomys olseni of the Cylindrodontidae in having the p4 trigonid basin open anteriorly; the lower molars with two anterior and one posterior root; the metalophid II extending from the protoconid toward the metaconid and enclosing a small trigonid basin; a short ectolophid bearing no mesoconid; the hypoconid projecting anterolabially; the entoconid separated from the posterolophid but connected with the ectolophid in front of the hypoconid by a complete hypolophid; the metastylid crest and entoconid separated by a narrow gap at the lingual edge of the tooth; a strong posterolophid bearing no hypoconulid; and the lower incisor with uniserial enamel ultrastructure. It differs from A. olseni in having a rounded ventral surface on the lower incisor; the molar teeth lower crowned and the trigonid higher than the talonid; the lophs and lophids narrower and less well developed; the hypoconid not unicuspal hypsodont; the anterior part of the talonid basin wide open; and a lower metastylid crest bordering the lingual margin of molars. A recent proposal of a sister group relationship between Cylindrodontidae and Ctenodactylidae is reviewed and is rejected because of insufficient evidence. The possibility that the Cylindrodontidae are related to sciuromorphs, particularly Sciuridae and Aplodontidae, is speculated; these taxa may have been derived from an ischyrornyid stock.
18 p. : ill. ; 26 cm.
Includes bibliographical references (p. 15-18).