THE OLDEST KNOWN EOSPIRIFER (BRACHIOPODA) IN THE CHANGWU FORMATION (LATE ORDOVICIAN) OF WESTERN ZHEJIANG, EAST CHINA, WITH A REVIEW OF THE EARLIEST SPIRIFEROIDS

Eospirifer praecursor n. sp. is the oldest known eospiriferine, probab ly ancestral to the entire Spirifer group. It is described here based on external and internal mold material from the uppermost part of the Changwu Formation (mid-Ashgill, Late Ordovician), Hejiashan, Jiangshan , western Zhejiang, East China. A study of the ontogeny of E. praecurs or n. sp. suggests that the cardinalia of early growth stages are more similar to those of early atrypoids rather than to those of the ortho ids but the brachidia in these earliest Eospirifer are still unknown. The possibility that eospiriferines were derived from an atrypoid stoc k cannot be excluded. All early eospiriferine species recorded from th e Ashgill, Rhuddanian, and early Aeronian are reviewed for comparison. Their morphological diversification reveals early evolutionary experi mentation. Based on the Ashgill occurrence of Eospirifer, it is likely that East Asia may be considered as one of the eospiriferine source a reas.