Data from: 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 the early odontocete radiation in the Oligocene, along with other taxa such as the Ashleycetidae, Mirocetidae, Patriocetidae, Simocetidae, Waipatiidae, and Xenorophidae. Based on this new understanding, Agorophiidae are known with certainty only from the early Oligocene of South Carolina, with other undescribed, potential agorophiid specimens from the Oligocene of the North Pacific region (Japan, Mexico, and Washington State).

侏儒始喙鲸（Agorophius pygmaeus）的正模部分头骨（该属与始喙鲸科均为单型类群）已失踪近140年。自侏儒始喙鲸被发现以来，先后有诸多分类单元与标本被归入始喙鲸科，随后又被重新分类并移出该科，这造成了学界对何为始喙鲸类的认知混乱，同时也使得始喙鲸科的鉴别特征始终未能明确。近日，一件采自美国南卡罗来纳州阿什利河水下崖壁的始喙鲸类新头骨标本被归入侏儒始喙鲸，其产出层位为阿什利组底部（渐新世早期）。该新标本保存了大部分头骨与听泡骨（periotics），其保存状态完好，且是始喙鲸类中首次被详细描述的听泡骨材料。该新标本为始喙鲸科的正式界定提供了契机，同时可将该属与该种置于渐新世早期齿鲸类辐射演化的系统发育框架中，一同纳入讨论的类群还包括阿什利鲸科（Ashleycetidae）、迷鲸科（Mirocetidae）、爱国鲸科（Patriocetidae）、西莫鲸科（Simocetidae）、怀帕蒂鲸科（Waipatiidae）以及异喙鲸科（Xenorophidae）。基于这一新的研究认知，目前确凿的始喙鲸科化石仅发现于美国南卡罗来纳州的渐新世早期地层；而北太平洋区域（日本、墨西哥与华盛顿州）的渐新世地层中，亦存在未被正式描述的疑似始喙鲸类标本。