Godfrey et al.—New specimen of Agorophius pygmaeus (Odontoceti, Cetacea)
tooth were both missing in 1907 (True, 1907), and Fordyce (1981) gives an extremely thorough discussion of the history and possible whereabouts of the skull as well as the rediscovery of the holotype tooth. The holotype tooth is described in detail by Fordyce
(1981), who rediscovered the mislabeled tooth in the MCZ collection. He notes that the crown bears three anterior and three posterior denticles, and that the two roots are joined by an isthmus proximal to the crown. The crown shape is very triangular and it is much taller (12.7mm) than long (7.5 mm).
Type locality.—Greer’s Landing, South Carolina (Tuomey, 1848), bed of the Ashley River about 10 miles from Charleston (Tuomey, 1847a, 1847b), PBDB collection 45761. Greer’s Landing is in the general vicinity of Middleton Place Gardens, on the west bank of the Ashley River approximately 20.2km (12.5 miles) upriver from Charleston, in Dorchester County, South Carolina, USA (after Whitmore and Sanders, 1977), at approximately 32° 54' N, 80° 8'W(Fordyce, 1981). Additional efforts to precisely locate Greer’s Landing have not produced results. Besides Tuomey (1848), Greer’s Landing is also mentioned by Ruffin (1843) as a site where carbonate of lime was mined, with no additional information. Census records from 1850 indicate the presence of a family with the surname of Greer living in the area, (then known as Charleston County, St. Andrews Parish) but these records do not specify an exact address or location.
Age and distribution.—The holotype skull of Agorophius pygmaeus probably came from the upper part of the Rupelian Ashley Formation (Fordyce, 1981). Specimen ChM PV4256 (Fig. 2) was recovered from the Chattian Chandler Bridge Formation, at Leveston Bluff, PBDB collection 156031. The Ashley Formation was previously considered Chattian
(late Oligocene) in age by older authors (Katuna et al., 1997; Koretsky and Sanders, 2002; Sanders and Barnes, 2002a) and Rupelian (early Oligocene) by more recent authors (Geisler and Sanders, 2006; Weems and Sanders, 2014; Weems et al., 2004). All specimens of A. pygmaeus are known from the greater Charleston, South Carolina, USA region and range in age from Rupelian to Chattian.
Referred specimens.—Fordyce (1981) restricted the species to the holotype specimen only. Given that the holotype skull was so well figured (see Fig. 1), we think that additional specimens can be referred to Agorophius pygmaeus. Geisler et al. (2012) list specimen ChM PV4256 (Fig. 2) as belonging to Agorophius pygmaeus, following Geisler and Sanders (2003). This specimen is from the Chattian Chandler Bridge Formation and was collected underwater from the bed of the Edisto River. Measurements of the skull are illustrated in Supplemental Material in Deméré et al. (2008) list ChM PV4256 as well as ChM PV5852 as Agorophius sp. Here, we follow Geisler and Sanders (2003) and Geisler et al. (2012) and identify ChM PV4256 as Agorophius pygmaeus, and follow Geisler et al. (2011) in identifying ChM PV5852 as Odontoceti indet., pending additional study of the specimen. We also identify a new partial skull, SC 2015.51.1 (Figs. 3–7), as Agorophius pygmaeus, which is described below.
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Diagnosis.—Cetacean with key odontocete synapomorphy of an ascending process of maxilla that is expanded posteriorly and laterally to overlap dorsal surface of supraorbital process of frontal (Barnes, 1990; Fordyce, 1994; Geisler and Sanders, 2003; Heyning, 1989; Messenger and McGuire, 1998; Miller, 1923; Uhen, 2010). Odontocete in which an intertemporal constriction is present. An intertemporal constriction is a con- dition in which the parietals and interparietal broadly separate the face from supraoccipital (Mead and Fordyce, 2009). This differentiates Ashleycetidae, Mirocetidae, Xenorophidae, Simocetidae, and Agorophiidae from the clade of odontocetes including Patriocetidae and more derived odontocetes, which all lack an intertemporal constriction. Among the basal odontocetes that possess an intertemporal
constriction, Agorophius pygmaeus has a premaxillary sac fossa that lies mostly anterior to its antorbital notch but approximately one quarter of its length does reach posterior to the level of the notch (premaxillary sac fossa anterior to antorbital notch in Xenorophidae and Simocetidae, mostly posterior to antorbital notch in Waipatiidae); premaxillary cleft is deeply imbedded in the body of the bone immediately anterior to sigmoid curve of the posteroexternal plate (no cleft in Xenorophidae, pre- maxillary cleft presents as a shallow groove in Simocetidae and Waipatiidae); sigmoid curve of the posteroexternal plate lies opposite the middle of the length of the orbit (level to posterior margin of orbit in Xenorophidae [if present at all], absent in Simocetidae, well posterior to orbit in Waipatiidae); external nares open approximately at the level of the antorbital notch (behind notch in Xenorophidae, ahead of notch in Simocetidae, well posterior notch in Waipatiidae); single posterior dorsal infraorbital foramen in each maxilla at about the midpoint in the length of the orbit (absent in Xenorophidae, two per maxilla present in Simocetidae at midpoint in orbit length, two present [i.e., maxillary foramina] posterior to orbit in Waipatiidae); posterior margin of maxilla extends posterior to premaxilla but not posterior to postorbital process of frontal (premaxilla extends further posterior in Xenorophidae, maxilla extends further posterior to both premaxilla and postorbital process of frontal in Simocetidae and Waipatiidae); multiple supraorbital foramina in frontals between posteromedial margins of pre- maxilla (no such foramina in Xenorophidae or Waipatiidae, present in Simocetidae); parietals contribute to the dorsal intertemporal region of the skull without the presence of a sagittal crest (i.e., between the posterior margin of the frontals and the anterior margin of the supraoccipital), (sagittal crest present in Xenorophidae, absent in Simocetidae, no possibility of a parietal crest in Waipatiidae because parietals excluded from skull roof); in dorsal view, supraoccipital thrust forward anterior to line running from the angle formed by the zygomatic process of the squamosal within the temporal fossa to the other (apex of supraoccipital behind level of zygomatic angle in Xenorophidae, Simocetidae, and Waipatiidae); in lateral view, skull presents a horizontal profile (tabular dorsally) between the nasofrontal suture and the anterior margin of the supraoccipital; width of the skull at the level of the temporal fossae nearly twice as wide as deep. The single known buccal tooth (following the terminology
of Rothausen (1968) can be used to differentiate Agorophius pygmaeus from almost all other Oligocene taxa for which teeth
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