Data from: A new specimen of Agorophius pygmaeus (Agorophiidae, Odontoceti, Cetacea) from the Early Oligocene Ashley Formation of South Carolina, U.S.A.

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, U.S.A., 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, as yet undescribed, potential agorophiid specimens from the Oligocene of the North Pacific.

侏儒始豚（Agorophius pygmaeus）的正模（holotype）部分头骨标本——该属（Agorophius）与始豚科（Agorophiidae）均为单型类群——已遗失约140年。自侏儒始豚被发现以来，已有诸多类群与标本被归入始豚科，但后续均被重新分类并移出该科，这导致学界对哪些类群属于始豚科、哪些不属于产生了混淆，同时也未能明确界定始豚科的鉴别特征。近日，研究人员在美国南卡罗来纳州阿什利河的水下崖壁中采集到一件新发现的始豚科动物头骨，经鉴定归属于侏儒始豚；该标本产自阿什利组底部地层，时代为渐新世早期（Early Oligocene）。这件新标本保存了大部分头骨与听泡（periotics），其保存状态完好，且是始豚科动物中首次被详细记述的听泡结构。该新标本为界定始豚科的分类特征提供了契机，也使得我们能够将该属与该种置于渐新世早期齿鲸（odontocete）辐射演化的系统发育框架中，同时可与阿什利豚科（Ashleycetidae）、迷豚科（Mirocetidae）、父豚科（Patriocetidae）、似豚科（Simocetidae）、怀帕蒂豚科（Waipatiidae）以及异豚科（Xenorophidae）等类群开展对比研究。基于这一新的研究认识，目前确凿的始豚科标本仅发现于美国南卡罗来纳州的渐新世早期地层中，北太平洋渐新世地层内尚有若干尚未正式发表的疑似始豚科标本。