中国科学院南京地质古生物研究所机构知识库

Material from two Upper Cambrian horizons in north-western Hunan, China, represents two new species of Shumardiidae. These provide important information concerning the morphology and evolution of early members of this family of small trilobites. Oculishumardia hunania gen. and sp. nov., the type species of Oculishumardia, from the middle Huaqiao Formation (Youshian Stage), is the oldest-known shumardiid. Symplesiomorphic characters, possibly inherited from a ptychoparioid ancestor, include the presence of palpebral lobes, facial sutures and an anterior border. This suggests that the sighted condition may have been phylogenetically basal for the shumardiid clade, and O. hunania may represent an intermediate stage of evolution between eye-bearing ptychoparioids and more derived. generally eyeless, shumardiids. Akoldinioidia shanjiangensis sp. nov. from the overlying Shenjiawan Formation (upper Taoyuanian Stage) has five thoracic segments, two of which are macropleural. It may represent an intermediate stage in an evolutionary succession from Akoldinioidia dydimacantha to Acanthopleurella. Acanthopleurella may have been derived from a form comparable to A. dydimacantha by reduction both in holaspid size and in the number of holaspid thoracic segments. The hypostome in A. shanjiangensis suggests that shumardiids were characterised by a natant mode of hypostomal attachment.