Ordovician trilobites from the Yingan Formation of northwestern Tarim, Xinjiang, northwestern China

Abstract

Three trilobite species, Lisogorites mistus sp. nov., Taklamakania tarimensis W. T. Zhang and Ampyxinella rotundata W. T. Zhang, are described from the Yingan Formation near Kalpin in southern Xinjiang, NW China. They occur with graptolites in an assemblage of late Caradoc age. Lisogorites is an aberrant asaphid, and is considered to be a senior synonym of Trigonoaspis and Tangyaia. Ampyxinella is regarded as referable to the subfamily Endymioninae. The raphiophorid Taklamakania has only three thoracic segments and may have been derived from Ampyxina by neoteny. The morphological and taphonomical features of the trilobites suggest that this faunule lived on a soft muddy substrate in a quiet, deeper-water, slope environment of the ‘Raphiophorid Biofacies’. Palaeogeographically the Kalpin area was located on the northwestern slopes of the Tarim carbonate platform during Caradoc times. Closest zoogeographic relationships of this fauna are with South China, Kazakhstan, North China and eastern Australia.