Hurdiid radiodontans from the middle Cambrian (Series 3) of Utah

Radiodontan body elements, some belonging to Peytoia and Hurdia and some unassigned, have been reported from the Langston Formation (Spence Shale Member), Wheeler Formation, and Marjum Formation of the middle Cambrian (Series 3) of Utah. These identifications are reassessed in light of recent work on the morphology of the radiodontan Hurdia. New specimens of Hurdia are identified from the Spence Shale, representing mouthparts (oral cones), cephalic carapace H-elements, frontal appendages, and a single isolated swimming flap. The shape of the H-elements allows H. victoria Walcott, 1912 to be identified from the Spence Shale for the first time. The flap is larger and more complete than any reported from the Burgess Shale and allows for a better understanding of the morphology of Hurdia swimming flaps. A 3D model of a Hurdia frontal appendage indicates that there is only one morph of Hurdia frontal appendage found in both species, and apparent morphological differences between disarticulat...采自美国犹他州中寒武统（统3）兰斯敦组（Langston Formation，斯宾塞页岩段（Spence Shale Member））、惠勒组（Wheeler Formation）与马朱姆组（Marjum Formation）的放射齿类（radiodontan）躯体构件已有报道，其中部分归属于皮托虾（Peytoia）和赫德虾（Hurdia），其余暂未指定分类单元。结合近期针对放射齿类赫德虾形态学的研究进展，本次研究对上述鉴定结果进行了重新评估。研究从斯宾塞页岩中鉴定出全新的赫德虾标本，包括口器（oral cones，口锥）、头甲H构件（cephalic carapace H-elements）、前附肢（frontal appendages）以及一枚孤立的游泳肢（swimming flap）。通过H构件的形态特征，本次研究首次在斯宾塞页岩中鉴定出维多利亚赫德虾（H. victoria Walcott, 1912）。该游泳肢较布尔吉斯页岩（Burgess Shale）已报道的同类标本体型更大、保存更完整，有助于更深入地解析赫德虾游泳肢的形态特征。对赫德虾前附肢的三维模型（3D model）分析表明，两种赫德虾中仅存在一种形态的前附肢，而解离标本间存在显著的形态差异……