云南建水早第三纪哺乳类的发现

FIRST RECORD OF EARLY TERTIARY MAMMALS FROM SOUTHERN YUNNAN

本文记述了在云南省建水县岔科地区发现的哺乳动物化石。根据豫鼠(Yuomys),定地层时代为晚始新世。这套地层暂称岔科组,以示滇南地区第一个含早第三纪哺乳动物的地点和层位。

Some mammalian fossils wererecently collectedJianshui County, Yunnan Province by山e authors infrom the Late Eocene f hoke area,pring of 1987. It is the first record forthe Early Tertiary mammals in Southern Yunnan, though the Province is bundant in fossilsin many places. A rodent animal, Yuomys yutananensis sp. nov. of Ctenodactyloid familyuomyidae is ecognized in the present paper. Yuomys yunndnensis is represented by。lowerjaw with DPq-M2 and a proxitual`part of a right adius. Judging from the cheek teeth, thespecies is characterized by relatively big lower trigon; weak and elongated metalophid ; ra-her long metalophid IT,, connecting with the base of the metaconid; elongated and straight hy-polophid and comparatively xternally situated ectolophid. Together with the materials of Yuomys yuzznanensis, there are two broken lower jaws: onebearing posterior part of Mg is probably of a small Perissodactyla; the other with damagedP2-Mz may belong to Edentat-like nimal. }'hough the specimens are too broken to makedefinite determination, it is worth notice that some new forms seem o be occurred in theregion Up to the present, the genus Yuomys contains five species, ranging in age from the lateMiddle ocene to Late Eocene and restricting to China geographically. Among all the knownspecies, Yzsomys yzznnanensis is most similar o Y. caviodes morphologically, indicating thatthe age of the two fossil-bearing beds should be nearly, equivalent.— Late ocene. The outcrop of the Eocene deposits exposes excellently near the Choke Town. The se-diments can be divided into two arts: the lower part, yielding fossil mammals, consists ofownish-red mudstone and siltstone, seldom with grayish-green ltstone ntercalated; the upperis made up of alternating beds of brownish-red mudstone and grayish-green siltstone, with gre-en and rayish-white marl intercalated. The whole deposits exposed are about seven hundr-ed meters in thickness, According to Yuomys urezzazzensis, the strata, at least the lower part,are Late Eocene in age. For the purpose of use, the deposits are entatively called ChokeFormation.