Data from: An alternative interpretation of the Paleogene turtle Cardichelyon rogerwoodi as a hinged kinosternoid

Cardichelyon rogerwoodi is an enigmatic fossil turtle from the late
Paleocene to early Eocene of North America. Previous analyses suggested
affiliation with Testudinoidea, in particular the big-headed turtle
Platysternon megacephalum, based on the presence of multiple musk-duct
foramina and a large head. We here highlight previously undocumented
characteristics for this turtle, notably the presence of short costiform
processes, a rib-like axillary process, and a posterior plastral hinge.
Phylogenetic analysis places Cardichelyon rogerwoodi within Testudinoidea
but the exclusion of testudinoids suggest an affiliation with
Dermatemydidae. Using consilience with external data we favor placement
within Kinosternoidea. Cardichelyon rogerwoodi is therefore an aberrant,
hinged kinosternoid that developed in situ in North America during the
Paleocene long before the arrival of testudinoids on this continent in the
early Eocene.

罗杰伍德心壳龟（Cardichelyon rogerwoodi）是一种产自北美洲古新世晚期至始新世早期的神秘化石龟类。既往研究基于其具有多组麝腺导管孔（musk-duct foramina）以及头部硕大的特征，推测其隶属于龟总科（Testudinoidea），尤其与大头龟（Platysternon megacephalum）存在近缘关系。本文首次披露了该龟类此前未被记录的形态特征，具体包括短肋突（costiform processes）、类肋骨状腋突（axillary process）以及腹甲后铰链（posterior plastral hinge）结构。系统发育分析（phylogenetic analysis）结果显示，罗杰伍德心壳龟虽处于龟总科演化分支内，但当剔除龟总科类群后，其亲缘关系指向泥龟科（Dermatemydidae）。结合外部证据的一致性论证，我们更倾向于将其归入动胸龟总科（Kinosternoidea）。综上，罗杰伍德心壳龟是一类异常特化、带有铰链结构的动胸龟总科类群，于古新世时期在北美洲本土演化形成，远早于龟总科类群在始新世早期抵达该大陆的时间。