CYCLOPYGID TRILOBITES FROM THE ORDOVICIAN OF NORTHEASTERN TARIM, XINJIANG, NORTHWEST CHINA

Eight species of cyclopygid trilobites are descnbed from the late early Tremadoc and late L1andeiloearly Caradoc of the QueerquekeYaerdang mountain area, northeastern Tarim, Xinjiang, China. Three of them are new: Prosl'ectatrix exquisita, Microl'aria (Heterocyc!ol'yge) abunda and M. (Quadratapyge) Cllrva. The mesopelagic cyclopygids were mainly distributed along the marginal deep facies belt in Tarim, but only some of them were able to penetrate into shallow sites during the period of the great transgression. This indicates that different assemblages of cyciopygid genera may have lived at different depth levels in the water body. Morphological changes which took place during the ontogeny and phylogeny of cyclopygids were minimal, and only a few evolutionary lineages show local heterochronic evolution.

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