泥河湾盆地发现短喙象化石

本文记述泥河湾盆地河北蔚县两个地点发现的化石,它们被鉴定为短喙象类的?Anancus和Pentalopodon两个属。

NEW INFORMATION ON BREVIROSTRINAE FROM THE NIHEWAN BASIN IN YUXIAN COUNTY, HEBEI PROVINCE

Two broken teeth of brevirostrine elephantids, one of Pentalophodon sp. and one of Anancus sp. were discovered in Plio-Pleistocene on the right bank of the Huliuhe River near Beishuiquan town, in Yuxian County, Hebei Province, China. The former tooth is from brownred sandy clay deposits located at an elevation of 890 meters at Donggou (40°08′16″N,114°42′25″E). The latter is from grey gravels, associated at 930 meters above sea level, with Palaeoloxodon sp. and other taxa at Shuikugou (40°06′08″N, 114°43′28″E).Pentalophodon and Anancus are recognized as Neogene members of the Gomphotheriidae, both representing members of the subfamily Brevirostrmae. Several characters differentiate these from other genera in the Mastodontoidea. Both taxa's skulls are brachycephalic and brevirostral in form, the jaws are shortened as those of the elephantids. The pretrite and posttrite of the cheek teeth are alternating. Their molar enemel folds are often not accentuated or are lacking altogether. Some paleontologists have merged Pentalophodon into the genus Anancus, but we consider that they should remain two different genera because they are as yet represented by few fossil materials and the tooth form of Pentalophodon appears to be very different from that of Anancus. Specifically Anancus displays trefoils on its molars and more conules than does Pentalophodon.The highest visible terrace of the Huliuhe River near Beishuiquan town is part of the Cheng-chia-wan Platform named by G. B. Barbour in the Nihewan sedimentary basin in 1926. The terrace section of over 100 meters consists, from bottom to top, of four lithofacies: Jurassic rock,, brown-red sandy clay with gravel and calcareous concretion of Pliocene origin, fluviatile-lacustrine sediments of Lower-Middle Pleistocene age and the loess of Late Pleistoceneage. The brown-red sandy clay zone is about one-hundred meters thick.The fossil mammalian fauna discovered at Xiyaozitou, near Donggou has been divided by Wang Ande (1982) into two parts: the Yuxian Formation of Upper Pliocene age, with Viverra sp., Hipparion houfenense, Chilotherium sp., Gazella blacki, Antispiroides hopeiensis, Sinoryx sp. and other species, and the Huliuhe Formation of Lower Pleistocene age with Leporids, Canis multicuspus, Nyctereutes sinensis, Hipparion cf. hippidiodus, Paleotragus sp., Gazella blacki and other taxa. The Donggou locality which yielded the Pentalophodon sp. fossil probably corresponds with the Huliuhe Formation of Wang Ande. The Shuikugou locality yielding the Anancus sp. material is in the fluviatile-lacustrine sediment zone, situated approximately 1,200 meters north of the well-known Danangou locality from which Tang Yinjun (1980) collected many mammalian fossils, including Lynx variabilis, Zygolophodon sp., Hipparion sinense and others. The stratum yielding this fauna was named the Dongyaozitou Formation by Tang Yinjun and Ji Hongxiang (1983), assigned to the boundary between the Upper Pliocene and the Lower Pleistocene. The Shuikugou locality is about 50 meters abov the Danangou locality in the local section. Therefore, Anancus unexpectedly appears here with a Neogene fossil mammalian element, above the Plio-Pleistocene Danangou locality. This discovery of Anancus from the Shuikugou locality suggests that the Anancus genus survived into the Pleistocene or perhaps that the fossil has been redeposited from older strata through fluvial action.