A new specimen of Agorophius pygmaeus (Agorophiidae, Odontoceti, Cetacea) from the Early Oligocene Ashley Formation of South Carolina, USA

The holotype partial skull of Agorophius pygmaeus (the monotypic form for both the genus Agorophius and the Family Agorophiidae) has been missing for approximately 140 years. Since the discovery of Agorophius pygmaeus, many additional taxa and specimens have been placed in the Family Agorophiidae, only to be reclassified and removed later. This has created confusion as to what is and what is not an agorophiid and a lack of clarity as to what characteristics delimit the Agorophiidae. A newly discovered skull of an agorophiid recently collected from an underwater cliff face of the Ashley River, South Carolina, USA, is assigned to Agorophius pygmaeus. It derives from the base of the Ashley Formation (early Oligocene). The new specimen consists of most of the skull and periotics, which are well preserved and described for the first time in an agorophiid. The new specimen provides an opportunity to diagnose the Agorophiidae and place the genus and species within the phylogenetic context of t...小始喙鲸（Agorophius pygmaeus）的正模部分头骨（始喙鲸属（Agorophius）与始喙鲸科（Agorophiidae）均为单型类群）已失踪约140年。自该物种被发现以来，先后有诸多类群与标本被归入始喙鲸科，但后续均被重新分类并移出该科。这导致学界对始喙鲸科的类群界定产生混淆，同时也难以明确该科的鉴别特征。近日，一件新发现的始喙鲸类头骨从美国南卡罗来纳州（South Carolina）阿什利河（Ashley River）的水下崖壁中被采集，该标本被归入小始喙鲸，其产出层位为渐新世（Oligocene）早期的阿什利组（Ashley Formation）底部。该新标本包含大部分头骨与围耳骨（periotics），其保存状态完好，且为首次在始喙鲸科类群中对围耳骨进行正式描述。该新标本为界定始喙鲸科的鉴别特征提供了契机，并可将该属与种置于（原文截断）的系统发育框架中。