Journal of Paleontology, 90(1), 2016, p. 154–169 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2016.4


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


Stephen J. Godfrey,1 Mark D. Uhen,2 Jason E. Osborne,3 and Lucy E. Edwards4


1Department of Paleontology, Calvert Marine Museum, P.O. Box 97, Solomons, Maryland 20688, USA ⟨Godfresj@co.cal.md.us⟩ 2George Mason University, AOES Geology, MS 6E3, Fairfax, Virginia 22030, USA ⟨muhen@gmu.edu⟩ 3Paleo Quest, 4657 Sudley Road, Catharpin, Virginia 20143, USA ⟨paleoquest2@gmail.com⟩ 4926A National Center, U.S. Geological Survey, Reston, Virginia 20192, USA ⟨leedward@usgs.gov⟩


Abstract.—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).


Introduction


Globally, increasing numbers of Oligocene odontocetes are being named (Fordyce, 1994, 2002, 2004; Geisler et al., 2014; Uhen, 2008b [and references therein]; Uhen et al., 2008), which is beginning to fill in the perceived Oligocene cetacean diversity gap noted by Uhen and Pyenson (2007) and references therein. Within eastern North America, Oligocene cetaceans are known from around Charleston, South Carolina (Ashley, Chandler Bridge, and Tiger Leap Formations) and Onslow Beach, North Carolina (Belgrade Formation), (Uhen, 2008b) as well as an unnamed odontocete specimen from the Chickasawhay Formation of eastern Mississippi (Uhen, 2014). Agorophius pygmaeus (Agorophiidae) (Fig. 1) was among the first Oligocene odontocetes to be named from North America (Müller, 1849). Because its cranial morphology is, in many respects, intermediate between archaeocetes and Neogene odontocetes, it has played a central role in discussions of the bauplan from which later odontocetes evolved (Whitmore and Sanders, 1977). However, very unfortunately, the holotype specimen has been lost for the past 140 years, except for a single tooth, despite concerted efforts to locate the missing cranial material (Fordyce, 1981). In reviewing the long and tortuous history of the Agorophiidae, Fordyce (1981) concluded that


A. pygmaeus could not be reduced to a nomen dubium because of the existence of the aforementioned holotype tooth. However, until the holotype skull is rediscovered, that tooth does little to resolve the systematics of both A. pygmaeus and the Agorophiidae. Fordyce (1981) did hold out hope that the dis- covery of a topotypic skull with teeth might clarify the identity of the species and family. Here we offer a partial remedy because of the recent dis-


covery of another agorophiid partial skull that we attribute to Agorophius pygmaeus. However, with only a few illustrations of the holotype to go by (and because this new specimen does not preserve teeth), it is impossible to prove the conspecificity of the present skull. Although the two skulls are not identical, their dif- ferences do not rise to the level of placing the newly found skull in a new agorophiid species (see below). Consequently, we are now able to establish the character states of many additional cranial features for Agorophius pygmaeus.Furthermore,thisnew speci- men provides an opportunity to more accurately include this family in a phylogenetic analysis of early odontocetes.


Systematic paleontology


Abbreviations.—ChM PV, Charleston Museum, Vertebrate Paleontology collection, Charleston, South Carolina;


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