The oldest knownEospirifer(Brachiopoda) in the Changwu Formation (Late Ordovician) of western Zhejiang, East China, with a review of the earliest spiriferoids

Abstract

Eospirifer praecursorn. sp. is the oldest known eospiriferine, probably ancestral to the entireSpirifergroup. 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 ofE. praecursorn. sp. suggests that the cardinalia of early growth stages are more similar to those of early atrypoids rather than to those of the orthoids but the brachidia in these earliestEospiriferare still unknown. The possibility that eospiriferines were derived from an atrypoid stock cannot be excluded. All early eospiriferine species recorded from the Ashgill, Rhuddanian, and early Aeronian are reviewed for comparison. Their morphological diversification reveals early evolutionary experimentation. Based on the Ashgill occurrence ofEospirifer, it is likely that East Asia may be considered as one of the eospiriferine source areas.