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

Published online by Cambridge University Press:  15 June 2016

Stephen J. Godfrey,
Mark D. UhenOpen the ORCID record for Mark D. Uhen[Opens in a new window],
Jason E. Osborne and
Lucy E. Edwards
Stephen J. Godfrey
Affiliation:
Department of Paleontology, Calvert Marine Museum, P.O. Box 97, Solomons, Maryland 20688, USA 〈Godfresj@co.cal.md.us〉
Mark D. Uhen
Affiliation:
George Mason University, AOES Geology, MS 6E3, Fairfax, Virginia 22030, USA 〈muhen@gmu.edu〉
Jason E. Osborne
Affiliation:
Paleo Quest, 4657 Sudley Road, Catharpin, Virginia 20143, USA 〈paleoquest2@gmail.com〉
Lucy E. Edwards
Affiliation:
926A National Center, U.S. Geological Survey, Reston, Virginia 20192, USA 〈leedward@usgs.gov〉
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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).

Information

Type
Articles
Information
Journal of Paleontology , Volume 90 , Issue 1 , January 2016, pp. 154 - 169
Copyright
Copyright © 2016, The Paleontological Society 

Introduction

Globally, increasing numbers of Oligocene odontocetes are being named (Fordyce, Reference Fordyce1994, Reference Fordyce2002, Reference Fordyce2004; Geisler et al., Reference Geisler, Colbert and Carew2014; Uhen, Reference Uhen2008b [and references therein]; Uhen et al., Reference Uhen, Fordyce and Barnes2008), which is beginning to fill in the perceived Oligocene cetacean diversity gap noted by Uhen and Pyenson (Reference Uhen and Pyenson2007) 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, Reference Uhen2008b) as well as an unnamed odontocete specimen from the Chickasawhay Formation of eastern Mississippi (Uhen, Reference Uhen2014). Agorophius pygmaeus (Agorophiidae) (Fig. 1) was among the first Oligocene odontocetes to be named from North America (Müller, Reference Müller1849). 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, Reference Whitmore and Sanders1977). 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, Reference Fordyce1981). In reviewing the long and tortuous history of the Agorophiidae, Fordyce (Reference Fordyce1981) 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 (Reference Fordyce1981) did hold out hope that the discovery of a topotypic skull with teeth might clarify the identity of the species and family.

Figure 1

Partial skull of Agorophius pygmaeus. Type specimen. Plate of Phocodon holmesii Agassiz, reproduced and edited in Adobe Photoshop® from True (Reference True1907): (1) right lateral view; (2) left lateral view; (3) dorsal view; (4, 5, 6) single tooth in medial, lateral, and posterior views respectively. The scale is based on the “greatest breadth” of the skull given by True (Reference True1907) as 7.5 in. Unfortunately, that dimension does not proportionately correspond to the maximum length of the skull given as 14.5 in. The greatest breadth dimension was chosen to calibrate the scale in this image because based on what is preserved that dimension could not be any larger, whereas some of the original measured length of the skull could have been lost prior to this illustration having been made. Scale bar represents 10 cm.

Here we offer a partial remedy because of the recent discovery 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 differences 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, this new specimen 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; MCZ, Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts; PBDB, Paleobiology Database, paleobiodb.org; SC, South Carolina State Museum, Columbia, South Carolina; USNM, United States National Museum of Natural History, The Smithsonian Institution, Washington, D.C.

Order Cetacea Brisson, Reference Brisson1762

Pelagiceti Uhen, 2008

Neoceti Fordyce and de Muizon, Reference Fordyce and de Muizon2001

Suborder Odontoceti Flower, Reference Flower1867

Family Agorophiidae Abel, Reference Abel1914

Type genus

Agorophius Cope, 1895a

Included genera

Type and only genus, Agorophius Cope, 1895a

Diagnosis

As for the only included species, Agorophius pygmaeus, in the only included genus, Agorophius, see below.

Comments

Fordyce (Reference Fordyce2002) stated that “the lithograph [of the holotype of Agorophius pygmaeus does not]… provide enough information to allow the Agorophiidae to be rediagnosed in a cladistic sense.” Given that Fordyce’s (Reference Fordyce1981, Reference Fordyce2002) concept of the Family Agorophiidae includes only the genus Agorophius and the species Agorophius pygmaeus; and given that Fordyce considers the species diagnosable (see below), the family must be diagnosable as well using these same characteristics as the species. Gingerich (Reference Gingerich2005) erected a superfamily Agorophioidea that included the families Agorophiidae, Simocetidae and Patriocetidae (?) without discussion. Subsequent phylogenetic analyses (Geisler et al., Reference Geisler, Godfrey and Lambert2012, Reference Geisler, Colbert and Carew2014; Sanders and Geisler, Reference Sanders and Geisler2015; Uhen, Reference Uhen2008b) have shown this assemblage of families to be polyphyletic, and thus the superfamily Agorophioidea is not recognized here.

Several authors previously included the genus Xenorophus in the Agorophiidae (Hay, Reference Hay1930; Miller, Reference Miller1923; Simpson, Reference Simpson1945), but it has been subsequently removed to its own family, the Xenorophidae (Uhen, Reference Uhen2008b). Likewise, the genus Archaeodelphis has also been placed in the Agorophiidae (Miller, Reference Miller1923; Rothausen, Reference Rothausen1968), but it too has been removed to the Xenorophidae (Geisler et al., Reference Geisler, Colbert and Carew2014; Uhen, Reference Uhen2008b). Rothausen (Rothausen, Reference Rothausen1968) also suggested that Microzeuglodon aff. caucasicum belonged in the Agorophiidae, but Microzeuglodon is now considered a nomen dubium (Uhen and Pyenson, Reference Uhen and Pyenson2007) and the status of the species Microzeuglodon aff. caucasicum remains unclear. Aslanova (Reference Aslanova1977) named a new genus and species Atropatenocetus posteocenicus based on a partial neurocranium and vertex from the Chattian of Azerbaijan, and placed it in the family Agorophiidae without justification. Neither descriptions nor photographs or illustrations of the specimen are clear enough for comparison to other Oligocene Odontoceti. Thus, Uhen (Reference Uhen2008b) placed Atropatenocetus in Odontoceti incertae sedis.

Several additional specimens have been identified previously as members of the Agorophiidae but not yet assessed in detail, nor have they been assigned to any particular genus or species. Interestingly, all of these additional specimens are from the North Pacific, rather than the North Atlantic where all of the specimens herein attributed to Agorophius pygmaeus are found (see below). These include the following specimens. Japan: PBDB collection 45787, Morawan, Morawan Formation, Chattian (Sawamura et al., Reference Sawamura, Kimura, Barnes and Furusawa1996), two specimens Agorophiidae indet. n. gen. n. sp., large species and Agorophiidae n. gen. n. sp. “very aberrant” agorophiid; PBDB collection 76045, Kitakyushu, Yamaga Formation, Chattian (Okazaki, Reference Okazaki1995), cf. Agorophiidae indet. Mexico, Baja California Sur: PBDB collection 45695, San Juan de la Costa, El Cien Formation, Chattian (Cruiz-Marin and Barnes, Reference Cruiz-Marin and Barnes1996), Agorophiidae indet.; PBDB 66429, Tembabichi, Chattian (Gonzalez-Barba, Reference Gonzalez-Barba2007), Agorophiidae indet. U.S.A., Washington State: LACMVP 5984, PBDB collection 45807, Makah Formation, Rupelian (Goedert et al., Reference Goedert, Squires and Barnes1995) “Agorophiidae” indet.; LACMVP5112, PBDB collection 45809, Pysht Formation, Chattian (Goedert et al., Reference Goedert, Squires and Barnes1995), small “Agorophiidae” indet. None of these specimens has been adequately identified or described to determine if they are more closely related to Agorophius than any other Oligocene odontocete, and thus whether they belong in the Agorophiidae or some other clade. Until they are compared directly with the specimens described here as Agorophius pygmaeus, they should all be considered Odontoceti indet.

Agorophius Cope, 1895a

Type species

Zeuglodon pygmaeus Müller Reference Müller1849.

Included species

No other species besides the type species, Agorophius pygmaeus, are currently included in the genus Agorophius.

Diagnosis

As for the only included species, Agorophius pygmaeus, below.

Comments

Cope (Reference Cope1895) does not include any discussion of the etymology of the generic name Agorophius.

Agorophius pygmaeus (Müller, Reference Müller1849)

1847 Zeuglodon Gibbes, p. 8.

1847 Basilosaurus Gibbes, plate 5.

1847 Zeuglodon Tuomey, p. 284, figured.

1847 Zeuglodon (or Basilosaurus) Tuomey, p. 16, not figured.

1849 Zeuglodon pygmaeus Müller, p. 29, not figured.

1854 Basilosaurus pygmaeus Leidy, p. 8, not figured.

1868 Doryodon pygmaeus Cope, p. 155, not figured.

1869 Squalodon pygmaeus Leidy, p. 420, plate XXIX.

1869 Phocodon holmesii Agassiz (in Leidy)

1895 Agorophius pygmaeus Cope, p. 139, not figured.

1907 Agorophius pygmaeus True, p. 3, figured.

1914 Agorophius pygmaeus Abel, p. 202, figured.

1916 Squalodon pygmaeum Dal Piaz, p. 154, not figured.

1981 Agorophius pygmaeus Fordyce, p. 1029, figures 1–3.

Holotype

Fragmented but reassembled skull (Fig. 1) lacking ventral midline elements between orbits and basisphenoid, periotics and auditory bullae, and anterior portion of the rostrum; bearing a single right cheek tooth, figured by True from a plate prepared by Agassiz and labeled “Phocodon homesii” (True, Reference True1907). Only the cheek tooth remains, cataloged as MCZ 8761 (Fordyce, Reference Fordyce1981). True notes that the holotype skull and tooth were both missing in 1907 (True, Reference True1907), and Fordyce (Reference Fordyce1981) 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 (Reference Fordyce1981), 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 (12.7 mm) than long (7.5 mm).

Type locality

Greer’s Landing, South Carolina (Tuomey, Reference Tuomey1848), bed of the Ashley River about 10 miles from Charleston (Tuomey, Reference Tuomey1847a, Reference Tuomey1847b), PBDB collection 45761. Greer’s Landing is in the general vicinity of Middleton Place Gardens, on the west bank of the Ashley River approximately 20.2 km (12.5 miles) upriver from Charleston, in Dorchester County, South Carolina, USA (after Whitmore and Sanders, Reference Whitmore and Sanders1977), at approximately 32° 54' N, 80° 8' W (Fordyce, Reference Fordyce1981). Additional efforts to precisely locate Greer’s Landing have not produced results. Besides Tuomey (Reference Tuomey1848), Greer’s Landing is also mentioned by Ruffin (Reference Ruffin1843) 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, Reference Fordyce1981). 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., Reference Katuna, Geisler and Colquhoun1997; Koretsky and Sanders, Reference Koretsky and Sanders2002; Sanders and Barnes, Reference Sanders and Barnes2002a) and Rupelian (early Oligocene) by more recent authors (Geisler and Sanders, Reference Geisler and Sanders2006; Weems and Sanders, Reference Weems and Sanders2014; Weems et al., Reference Weems, Self-Trail and Edwards2004). 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 (Reference Fordyce1981) 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. (Reference Geisler, Godfrey and Lambert2012) list specimen ChM PV4256 (Fig. 2) as belonging to Agorophius pygmaeus, following Geisler and Sanders (Reference Geisler and Sanders2003). 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. (Reference Deméré, McGowen, Berta and Gatesy2008) list ChM PV4256 as well as ChM PV5852 as Agorophius sp. Here, we follow Geisler and Sanders (Reference Geisler and Sanders2003) and Geisler et al. (Reference Geisler, Godfrey and Lambert2012) and identify ChM PV4256 as Agorophius pygmaeus, and follow Geisler et al. (Reference Geisler, McGowen, Yang and Gatesy2011) 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.

Figure 2

Partial skull of Agorophius pygmaeus, ChM PV4256, The Charleston Museum, Charleston, South Carolina: (1) left lateral view; (2) dorsal view; (3) posterior (occipital) view; (4) ventral view of left maxilla showing posterior-most alveoli (anterior to the left). Scale bar represents 10 cm.

Figure 3

Partial skull of Agorophius pygmaeus, SC 2015.51.1a & b: (1) left facial/supraorbital region in dorsal view; (2) cerebral moiety in dorsal view; (3, 4) interpretive illustrations based on (1) and (2). (5) Line drawing to show how the two parts of the skull in (1) and (2) overlap. Scale bar represents 10 cm for (1) and (2).

Figure 4

Partial skull of Agorophius pygmaeus. SC 2015.51.1a & b: (1) left facial/supraorbital region in left lateral view; (2) left facial/supraorbital region in ventral view; (3) cerebral moiety in ventral view; (4) posterior (occipital) view; (5) cerebral moiety in right lateral view. Skull lightly coated with sublimed ammonium chloride. Scale bar represents 10 cm.

Figure 5

Restoration of the skull of Agorophius pygmaeus based on SC 2015.51.1 and ChM PV 4256.

Figure 6

Left periotic of Agorophius pygmaeus. SC 2015.51.1a: (1) periotic in situ in ventral view; (2, 3) stereo pairs of the left periotic. Scale bar for (1) represents 10 mm.

Figure 7

Partial right periotic of Agorophius pygmaeus. SC 2015.51.1c: (1) ventral view; (2) medial view; (3) dorsomedial view; (4) dorsal view. Scale bar represents 10 mm.

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, Reference Barnes1990; Fordyce, Reference Fordyce1994; Geisler and Sanders, Reference Geisler and Sanders2003; Heyning, Reference Heyning1989; Messenger and McGuire, Reference Messenger and McGuire1998; Miller, Reference Miller1923; Uhen, Reference Uhen2010). Odontocete in which an intertemporal constriction is present. An intertemporal constriction is a condition in which the parietals and interparietal broadly separate the face from supraoccipital (Mead and Fordyce, Reference Mead and Fordyce2009). 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, premaxillary 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 premaxilla (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 (Reference Rothausen1968) can be used to differentiate Agorophius pygmaeus from almost all other Oligocene taxa for which teeth are known. Most Oligocene Odontoceti that have buccal teeth with two roots have crowns that are much lower than Agorophius (Cotylocara, Patriocetus, Prosqualodon, Simocetus, Squalodon, Waipatia, Xenorophus), have too few denticles (Cotylocara, Saurocetus, Prosqualodon), too many denticles (Squalodon, Metasqualodon), or some combination thereof. The one taxon that has quite similar cheek teeth is Squalodon (Microzeuglodon) wingei (Ravn, Reference Ravn1926), which also has very high-crowned teeth similar to those of Agorophius pygmaeus, suggesting that this taxon may also represent an agorophiid, which are otherwise unknown from Europe.

Remarks

Leidy (Reference Leidy1854) states that the holotype specimen of Pontogeneus priscus Leidy Reference Leidy1852 , a cervical vertebral centrum, “may belong to” Agorophius pygmaeus (his Basilosaurus pygmaeus), but this opinion has not been followed by others and is almost certainly wrong given the large size of the centrum and likely late Eocene age of the specimen. See Uhen (Reference Uhen2005) for a discussion of Pontogeneus priscus, which is now considered a nomen dubium.

Fordyce (Reference Fordyce1981) stated that “… the holotype [of Agorophius pygmaeus] apparently lacks features diagnostic at or above the species level (but within the Odontoceti), the name Agorophius pygmaeus cannot be declared a nomen dubium, for the holotype cannot be examined to confirm the suspicion that it really does lack such features.” Fordyce (Reference Fordyce2002) later states that “the lithograph seems good enough to judge whether any new topotypic fossils might be conspecific with the lost holotype skull.” We agree, and think that these figures (reproduced here as Fig. 1) and the remaining tooth adequately document the diagnostic features of this species, and follow Geisler and Sanders (Reference Geisler and Sanders2003) and Geisler et al. (Reference Geisler, Godfrey and Lambert2012) in allowing other specimens to be referred to Agorophius pygmaeus.

Uhen et al. (Reference Uhen, Fordyce and Barnes2008) suggested that the teeth of the holotype specimen of Squalodon (Microzeuglodon) wingei from the Oligocene of Denmark (Ravn, Reference Ravn1926) might be conspecific with Agorophius pygmaeus. Rothausen (Reference Rothausen1970) placed this species in a new genus, Oligosqualodon, which Fordyce and de Muizon (Reference Fordyce and de Muizon2001) considered a nomen dubium. The teeth of S. (M.) wingei are sufficiently different to exclude conspecificity with A. pygmaeus, but the holotype specimen of S. (M.) wingei is not sufficiently diagnostic to warrant recognition as a separate species. Thus, both the genus Oligosqualodon and the species Squalodon (Microzeuglodon) wingei should be considered nomina dubia.

Agorophius pygmaeus, new specimen

Figures 3–7

Specimen

SC 2015.51.1. Partial skull comprising the neurocranium (SC 2015.51.1a), orbito-nasal region (SC 2015.51.1b), and right periotic (SC 2015.51.1c).

Locality

SC 2015.51.1 was discovered at site PQ-ARMP09 (PBDB collection 91482) and collected in situ three meters subsurface of mean high tide. The neurocranium was found disarticulated within inches of the left supraorbital/facial region; both pieces were lying above a lag deposit within the Ashley Formation. Site PQ-ARMP09 is located in the underwater cliff face of the Ashley River, in Dorchester County, South Carolina, USA, this site is likely near the type locality of Agorophius pygmaeus.

Surface collecting has been the primary way to find cetacean fossil specimens along the Atlantic Coastal Plain of South Carolina. The Ashley Formation has a limited number of subaerial exposures consisting of open pit mines, residential and commercial construction, and river banks. Most of these access points require permission from the landowner or development firm, and are often ephemeral. In addition, fossil specimens have been collected within river systems near Charleston by scuba divers for decades, facilitating the collection of specimens that would not otherwise be found.

Ashley Formation outcrops are often located along river systems where the damp marl above the water’s surface becomes somewhat lithified or “slightly case-hardened and yellow, but at river level it is usually soft and veiled” (Malde, Reference Malde1959). The exposed marl below the water’s surface becomes softer (i.e., puttylike) and more manageable for specimen extraction.

Formation and age

Ashley Formation, late Rupelian (Weems et al., Reference Weems, Self-Trail and Edwards2004; Weems and Sanders, Reference Weems and Sanders2014). Based on Nannoplankton (NP) stratigraphy, the Ashley Formation is referable to zone NP24 (Sanders and Barnes, Reference Sanders and Barnes2002a); mid-Oligocene (Rupelian) (Weems et al., Reference Weems, Self-Trail and Edwards2004). Strontium isotope stratigraphy has been used to date Oligocene beds in the Atlantic Coastal Plain (Harris and Fullagar, Reference Harris and Fullagar1991; Harris et al., Reference Harris, Mendrick and Fullagar2000). Glauconitic micas from the Ashley Formation yield Rb-Sr isochron dates of 26.2 ± 1.2 Ma. These dates are in agreement with the late Oligocene age assigned by previous authors (Harris and Fullagar, Reference Harris and Fullagar1991).

Analysis of a sediment sample taken immediately adjacent to the skull includes the presence of the dinoflagellates Saturnodinium pansum (Stover, Reference Stover1977; Brinkhuis et al., 1992) and abundant Chiropteridium spp., indicates an age of late early Oligocene to late (but not latest) Oligocene, correlative approximately with somewhere in NP23 to mid-NP25. This result is completely consistent with the NP24 (Rupelian) age assignment for the Ashley Formation. Appendix 1 in the Supplemental Material lists all of the dinoflagellate taxa identified in the sample.

Weems and Sanders (Reference Weems and Sanders2014) describe the depositional environment for the Ashley Formation as an offshore continental shelf, east of any barrier islands. The remains of sharks (Müller, Reference Müller1999), bony fishes, pancheloniid and dermochelyid sea turtles (Weems and Sanders, Reference Weems and Sanders2014) ), three nonmarine turtle taxa (Koretsky and Sanders, Reference Koretsky and Sanders2002), a large estuarine crocodile (Erickson and Sawyer, Reference Erickson and Sawyer1996), marine birds (including a large pseudodontorn), phocid pinnipeds (Koretsky and Sanders, Reference Koretsky and Sanders2002), dugongid sirenians (Domning, Reference Domning1997), and purportedly more than 20 taxa of early Neoceti (many of which have yet to be described) are now known from this formation (Erickson, Reference Erickson1990; Sanders, Reference Sanders1980; Sanders and Barnes, Reference Sanders and Barnes2002b; Whitmore and Sanders, Reference Whitmore and Sanders1977).

Description

General features

SC 2015.51.1 consists of a single partial skull preserved in two separate sections (Figs. 3–7), neither of which experienced much postmortem distortion. The larger portion includes most of the cerebral cranium, forward to the frontomaxillary suture and in situ periotics (the bullae were not preserved). The smaller piece preserves the median and left supraorbital/facial region back to the frontomaxillary suture and forward to the level of the premaxillary foramen; most of the rostrum was not preserved. There is no doubt that this skull derives from an odontocete; the maxillae and premaxillae telescope back over the supraorbital process of the frontal, a unique feature of odontocetes.

The skull appears nearly symmetrical in dorsal view (Fig. 3), except that the point of the apex of the supraoccipital wedge on the flattened (i.e., tabular) dorsal side of the parietals lies to the left of the midline of the skull. Measurements of the skull are illustrated in Supplemental Material Figure 2. The skull is approximately 206 mm wide across the zygomatic processes of the squamosals (an estimate because the left zygomatic process of the squamosal was not preserved), and it is 124 mm deep from the top of the parietal-supraoccipital suture down through the basioccipital hamuli; the skull is nearly twice as wide as deep. The width across the lambdoidal ridges above the occipital condyle approximates the aforementioned depth of the skull. The tabular intertemporal constriction is short, about as long as it is wide (minimum width equals 54 mm), and 83 mm deep. The skull is approximately 156 mm wide across the supraorbital processes of the frontals. At this same location, the skull is 92 mm deep as measured from the top of the left premaxilla vertically down through the palatine. At the level of the back of the tooth alveoli, the transverse ventral profile of the rostrum is convex ventrally.

Premaxilla

That portion of the left premaxilla that preserves the premaxillary sac fossa, the posteroexternal plate and the posterointernal process are all that remain. In dorsal view (Fig. 3.1, 3.3), the medial and lateral margins of the bone are nearly parallel on either side of the sac fossa. Contralateral premaxillae, at least in the area that is preserved, did not cover over the mesorostral canal giving the impression that it was open throughout its length. The premaxillary foramen is not preserved, however the posterolateral sulcus is, and it closely parallels the lateral margin of the bone through much of its length but disappears within the area of the posteroexternal plate. Medial to the posterior moiety of the sulcus is the premaxillary cleft that cuts a trough up to 5 mm deep as it courses posteromedially toward the posteroexternal plate (Fig. 3.1, 3.3). A sigmoid-shaped suture is formed between the posterior margin of the premaxilla and maxilla that separates the posteroexternal plate from the posterointernal process.

Maxilla

In dorsal view lateral to the premaxilla, two maxillary foramina (i.e., dorsal infraorbital foramina; the anteriormost one is 2 mm in diameter, the other 3.5 mm) occupy the space immediately anterior to the antorbital notch (Fig. 3.1, 3.3). Much of the overlapping supraorbital portion of the maxilla was not preserved. However, posterior to the sigmoid-shaped suture, some of the posteriormost part of the maxilla that overlapped the frontal remains.

Frontal

The skull is broken through the frontals where they suture with the maxillae and nasals (the latter of which are not preserved). In dorsal view (Fig. 3.3, 3.4), the lateral margin of the supraorbital margin of the frontal forms a straight border. The surface of the supraorbital region is coarsely textured having been covered by the maxilla in life. The postorbital processes were not preserved. On the anterior part of the cranial half of the skull, contralateral parts of the frontals abut/suture along their shared midline. On either side of the suture are clusters of tiny supraorbital foramina; between 0.5-1 mm in diameter. Lateral to these are the linear furrows that held the posteriormost extremity of the maxilla. The transverse coronal (i.e., frontoparietal) suture zigzags across the tabular intertemporal region of the skull.

In ventral view (Fig. 4.2), a tight cluster of at least six frontal foramina open in the roof of the orbit just anterior to the postorbital ridge. The optic infundibulum (and orbital fissure) lies immediately medial to these foramina (Fig. 4.1, 4.2).

Parietal

The tabular intertemporal face of the parietals preserves four posterolateral foramina at the level of the anterodorsal reach of the supraoccipital (Fig. 3.2, 3.4). There is no suggestion of a sagittal crest along the midline of the parietals. Below the concave dorsolateral margin of the parietal, the bone sweeps ventrolaterally to suture to the squamosal along an antero-ventrolaterally trending trough. At the point where the suture approaches the posterior margin of the intertemporal fossa, the parietal is bound ventrolaterally by a 10-mm-wide strip of the alisphenoid (as preserved), which in turn forms the subtemporal crest. Above this sutural contact, the concave lateral face of the parietals exhibit several shallow vascular furrows (Fig. 3.4).

Squamosal

The squamosal seems to contribute little to the lateral wall of the braincase. In dorsal view the suture between the parietal and squamosal lies along the floor of the temporal fossa. This fossa separates the lateral wall of the braincase from the zygomatic process of the squamosal. In dorsal view (Fig. 3), the zygomatic process is convex laterally and pointed anteriorly. It appears to have formed the widest part of the skull. In lateral view, it is convex dorsally and concave ventrally. For the most part, the surface of the bone is featureless.

Ventrally, the external auditory meatus lies immediately posterior to the postglenoid process (Figs. 4.3, 6). Medially, the wedge-shaped spiny process is formed by the converging anterior and posterior meatal crests. The long axis of the auditory meatus points directly toward the fenestra ovalis in the periotic (Figs. 4.3, 6). Anterior to the spiny process is the space occupied by the middle sinus (as seen in Simocetus; Fordyce Reference Fordyce2002, fig. 15). Medially, this second wedge-shaped area opens directly into the fossa incudis on the periotic. From this point forward, the falciform process takes shape. Unfortunately, neither process is complete. In SC 2015.51.1 (Figs. 4.3, 6), the complete left periotic lies immediately medial to the spiny process, the middle sinus, and the falciform process.

Supraoccipital

The supraoccipital figures prominently on the dorsal and posterior sides of the skull in SC 2015.51.1a (Figs. 3.2, 3.4, 4.4). Its anterodorsal margins (i.e., its apex) form a right-angle wedge separating the posterolateral foramina on the parietals. Here the thickness of the supraoccipital is barely raised above the level of the parietals. The apex lies to the left of the center of the tabular parietals, suggesting a slight degree of cranial asymmetry. Posterolaterally, the nuchal/lambdoid crest overhangs the parietal, squamosal, and exoccipital. Ventrally, the crest takes a sharp turn anterolaterally onto the zygomatic process of the squamosal where it soon disappears into the body of that bone. In general, the posterior surface of the supraoccipital is concave. However, a number of obvious protuberances rise from its surface and presumably mark the site of origin of epaxial musculature (including m. semispinalis). The external occipital crest is more accurately described as a midline protuberance within the anterodorsal third of the bone. Posteroventral to this protuberance the supraoccipital exhibits its most conspicuous concavity. Ventrally, the supraoccipital is inextricably fused to the exoccipital.

Exoccipital

The occipital condyles are twice as wide as they are high (Fig. 4.4). The condyles stand out on pedicles that nearly form a continuous concave trough around the perimeter of the condyles. A cluster of at least four foramina, approximately 1 mm in diameter, occupy the posterior face of the left exoccipital opening immediately lateral to the condyle (Figs. 3.2, 3.4, 4.3–4.5).

Periotic

Both periotics are preserved in situ contacting the squamosal (laterally), alisphenoid (anteriorly), parietal (dorsomedially), and paroccipital process posterodorsally (Figs. 6, 7). The left periotic is complete; however, some of the posterior process is missing from the right periotic. For that reason, the description will be based on the details evidenced primarily on the ventral face of the left periotic. The periotic in SC 2015.51.1 compares most closely to that of Simocetus (Fordyce, Reference Fordyce2002).

In ventral view, the long axis of the periotic (43.5 mm) forms an angle of 62 degrees to the long axis of the skull. The anterior process is convex laterally, slightly concave medially and conspicuously thickened (deep) dorsoventrally (Figs. 6, 7). The depth of the anterior process (17.5 mm) is greater than its length (15.5 mm) and it reaches its maximum thickness at its anteriormost end (i.e. the apex and ventral-most end of the laterally bowed anterior keel). The bullar facet, a shallow 10-mm-long groove, occupies the lengthwise ventral face of the anterior process. The fovea epitubaria separates the posterior end of the bullar facet from the body of the periotic. The fovea is bounded laterally by an indentation that marks the anterolateral sulcus (Fig. 7), and medially by a ridge and groove complex that parallels the long axis of the bone, which in turn separates the fovea from the pars cochlearis. The aforementioned ridge and groove complex occupies the area identified by Fordyce (Reference Fordyce2002) in Simocetus as having held the origin of the tensor tympani. Furthermore, as in Simocetus Fordyce (Reference Fordyce2002), the anterolateral sulcus marks the path of the middle meningeal artery.

Posterior to the fovea is the mallear fossa, a shallow 4 mm-wide hemispherical concavity that faces mostly posteroventrally, but also slightly laterally. Lateral to the mallear fossa, the lateral tuberosity is tightly pressed up against the squamosal just anterior to the spiny process and the anterior meatal crest. Two tiny notches mark the bone between the fossa and the pars cochlearis. Behind the mallear fossa lays the fossa incudis, which is bound laterally by the anterior meatal crest and medially by the facial sulcus. Immediately adjacent to the facial sulcus is the fenestra ovalis (neither stapes, nor other auditory ossicles were preserved), both of which lay medial to the spiny process and the external auditory meatus.

As in Simocetus, the pars cochlearis is long and narrow (approximately 16 mm×8 mm respectively) with a tabular ventral surface. A small ridge marks the antero-internal angle of the pars cochlearis. The fenestra rotunda is centered within the slightly concave posterior face of the pars cochlearis. Posterolaterally, the pars cochlearis is drawn out into a cochlear crest (Fordyce, Reference Fordyce2002). A distinct ridge emerges from the fenestra rotunda passing posteromedially before turning dorsally around the back of the pars cochlearis.

The distal opening of the facial canal opens between the fenestra ovalis and the fossa incudis. Posteriorly, the fossa that held the stapedial muscle is visible in ventral view between the posteromedial margin of the pars cochlearis (the cochlear crest) and the posterior bullar facet. The long axis of the fossa points toward the paroccipital process.

The long axis of the posterior bullar facet of the periotic lies at about a 45 degree angle to the length of the skull. Most of this facet lies directly behind the posterior meatal crest. Distally, the posteriormost portion of the periotic re-curves posteriorly.

The cranial surface of the cochlear portion of the periotic features the raised rim of the internal acoustic meatus. Within the anterior third of the meatus, the transverse crest separates the proximal opening of the facial canal from the dorsal vestibular area (Fig. 7.3). Posterior to this ovoid opening is the aperture for the cochlear aqueduct. The circular aperture for the endolymphatic duct (vestibular aqueduct) is positioned immediately posterolateral to the acoustic meatus. Passing forward from the endolymphatic duct is an elongated and inverted V-shaped trough that parallels the lateral edge of the internal acoustic meatus, occupying the space between the meatus and the dorsal crest of the periotic.

Within the larger context of cetacean ability to perceive water-borne sound, the dorsolateral and lateral sides of the periotic in SC 2015.51.1 abut the squamosal approximately to the same extent as that illustrated for Squalodon by Luo and Gingerich (Reference Luo and Gingerich1999, fig. 27c “reduced sq. contact”). In SC 2015.51.1, there does not appear to be any contact between the periotic and the exoccipital; decidedly derived over the condition in Dorudon (Luo and Gingerich, Reference Luo and Gingerich1999, fig. 27a), but not nearly as derived as in extant odontocetes (where the petrotympanic complex is enclosed in a peribullar cavity, isolated from the rest of the cranium) (Luo and Gingerich, Reference Luo and Gingerich1999, fig. 27d).

Cladistic analysis

Methods

To determine the phylogenetic relationships of SC 2015.51.1, we coded this specimen according to the morphological characters (to the extent to which they were preserved) listed in Geisler et al. (Reference Geisler, Godfrey and Lambert2012, Reference Geisler, Colbert and Carew2014) and Sanders and Geisler (Reference Sanders and Geisler2015). We also reappraised the codings for the holotype specimen based on the tooth MCZ 8761 and existing lithographs, as well as ChM PV4256 and treated all three specimens as separate operational taxonomic units (OTUs) to test the hypothesis that all three specimens represent the same taxon. The matrix consisting of three outgroup taxa and 83 ingroup taxa coded for 313 characters is included here as Appendix 2 in the Supplemental Material. The matrix was analyzed using PAUP 4b10 using the heuristic search option with 10,000 replicates and a random addition sequence of taxa. Characters were weighted following Sanders and Geisler (Reference Sanders and Geisler2015) such that ordered multistate characters were down-weighted so that their minimum length was equal to the minimum length of binary characters (i.e., one step).

Results

Six equally most parsimonious trees of length 184,859 were generated by the analysis. The strict consensus of the six trees is shown in Figure 8. The three specimens suspected to represent Agorophius pygmaeus all cluster together in a polytomy, and this polytomy is unambiguously placed near the base of the odontocete clade.

Figure 8

Cladogram of relationships of Neoceti, with a focus on the basal relationships among Odontoceti. Specimens included in Agorophius pygmaeus are shown in the box outlined with dotted lines. Several clades are identified with circles, including: Ag, Agorophiidae; Ba, Balaenopteroidea; De, Delphinidae; Eo, Eomysticetidae; In, Iniidae; Li, Lipotidae; Ph, Physeteroidea; Pl, Platanistoidea; Xe, Xenorophidae; Zi, Ziphiidae.

Remarks

Because all of the three specimens suspected of representing Agorophius pygmaeus cluster in a polytomy, the hypothesis that they all represent the same taxon is supported. That said, the three specimens that we assigned to Agorophius pygmaeus (MCZ 8761, ChM PV4256, and SC 2015.51.1) are not identical. In ChM PV4256 and SC 2015.51.1 for example, a V-shape best describes the outline of the anterodorsal margin of the supraoccipital, whereas in MCZ 8761, that margin is parabolic. Conversely, MCZ 8761 and ChM PV4256 possess four or more dorsal infraorbital foramina in each maxilla, whereas in SC 2015.51.1 only two appear to have existed. In ChM PV4256, the posterior-most maxillary alveolus is further removed from the antorbital notch than in SC 2015.51.1 (compare Figs. 2.4 and 4.2). We would ascribe these differences to intraspecific variation; none of which warrant the placement of these specimens in anything other than Agorophius pygmaeus.

With the assignment of both ChM PV4256 and SC 2015.51.1 to Agorophius pygmaeus, it is now possible to accurately characterize the family and thankfully, we can now move beyond the problems created by not knowing the whereabouts of the type. Although much more remains to be learned about the osteology of Agorophius pygmaeus, identifying some of the morphological features that characterize the family should facilitate the assignment of undescribed odontocetes to the Agorophiidae or not. Obviously, this monotypic family exhibits little morphological variation as compared to the more diverse Xenorophidae (Geisler et al., Reference Geisler, Colbert and Carew2014; Uhen, Reference Uhen2008b). Some of that inequity will diminish as more agorophiids are added to its ranks, and known taxa are reappraised in the light of the specimen described herein. In light of the phylogeny presented here, and in other recent publications (Geisler et al., Reference Geisler, Godfrey and Lambert2012, Reference Geisler, Colbert and Carew2014), Xenorophidae (inclusive of Archaeodelphis contra; Sanders and Geisler, Reference Sanders and Geisler2015) is the most plesiomorphic clade of Odontoceti (albeit with some synapomorphies of their own) followed by the Ashleycetidae (Ashleycetus planicephalus), then Mirocetidae (Mirocetus riabinini) (Sanders and Geisler, Reference Sanders and Geisler2015), followed by Agorophiidae (Agorophius pygmaeus + ChM PV 4178). Agorophiids exhibit odontocete symplesiomorphies that differentiate it from archaeocetes and mysticetes (following Geisler and Sanders, Reference Geisler and Sanders2003 and references therein): lacrimal and jugal form posterior wall of the antorbital notch; premaxillary foramina present; premaxillary sac fossa mostly anterior to the antorbital notch; dorsal infraorbital foramina anterior to the antorbital notch; maxilla covers most of the supraorbital process of the frontal; posterior edge of nasals in line with gap between postorbital and zygomatic processes; nasals elevated above the rostrum (Uhen et al., Reference Uhen, Fordyce and Barnes2008). Many of these odontocete symplesiomorphies, that give them an archaic odontocete look, relate to the degree to which its skull is telescoped.

At first glance, what distinguishes Agorophius pygmaeus from Neogene and Recent odontocetes are not its autapomorphies but rather its most conspicuous plesiomorphy; i.e., parietals contributing to the skull roof comprising the intertemporal constriction. This easily identifiable plesiomorphy, inherited from basilosaurid archaeocetes, disappears from Oligocene odontocetes between Simocetidae (where the parietals still contribute prominently to the skull roof) and the more derived Patriocetidae (where the parietals are expressed only as a narrow crescent between the frontals and the supraoccipital). Other archaeocete characteristics include temporal fossae open dorsally, prominent nuchal (lambdoid) crests, broadly exposed palatines (Fordyce, Reference Fordyce2002), two-rooted cheek teeth, multiple accessory denticles on the teeth, and a heterodont dentition (Uhen, Reference Uhen2008b).

Conclusions

For much of the 20th century, the Agorophiidae had been considered to include both the phylogenetically and geologically oldest odontocetes (Fordyce, Reference Fordyce1981, Reference Fordyce2002). However, the loss of all but a single tooth of the type specimen of the type genus and species (Agorophius pygmaeus) upon which the family Agorophiidae was based frustrated attempts to clearly diagnose the family (beyond symplesiomorphies confirming its status as a grade family) and add to its ranks with any confidence species that share familial autapomorphies (Fordyce, Reference Fordyce1981, Reference Fordyce2002). The disciplined approach taken by Fordyce (Reference Fordyce1981, Reference Fordyce2002) to abandon the grade family Agorophiidae has paid off with the establishment of several families of Oligocene odontocetes: the Ashleycetidae and Mirocetidae (Sanders and Geisler, Reference Sanders and Geisler2015), the Simocetidae (Fordyce, Reference Fordyce2002) and Xenorophidae (Uhen, Reference Uhen2008b). In recent phylogenetic analyses of cetaceans (Geisler, Reference Geisler2001; Geisler et al., Reference Geisler, Godfrey and Lambert2012, Reference Geisler, Colbert and Carew2014), these families, along with the Agorophiidae, comprise the most archaic odontocetes presently known.

It comes as no surprise to us that the Agorophiidae was considered central to odontocete origins and early evolution. The relatively few uniquely derived features exhibited by this family results in its basal position within the odontocete clade. When one compares that number to the many easily identifiable autapomorphies exhibited by xenorophids and simocetids, little wonder Agorophius pygmaeus featured so prominently in discussions of early odontocete evolution; it displays many characteristics that are intermediate between archaeocetes and more derived odontocetes. That there are some morphologically unexpected or unusual Oligocene odontocetes is suggestive of an early odontocete radiation, about which we are only beginning to learn.

Acknowledgments

The first two authors contributed equally to this publication. Additional preparation work on SC 2015.51.1 was completed by J. Velez-Juarbe and A. Jukar, including extraction of the periotic (SC 2015.51.1c) for study. D. Cicimurri, N. Pyenson, D. Bohaska, and J. McCormick kindly provided liberal access to the fossil odontocetes in their care. We extend out sincerest thanks to J. Pojeta for the use of his lab where SC 2015.51.1 was whitened with sublimed ammonium chloride. We have also benefitted greatly from discussions with R. E. Fordyce on how best to interpret this specimen. J. H. Geisler kindly helped integrate the data matrices from several previous publications prior to the addition of data for our phylogenetic analysis. The authors would also like to thank Coral Edge Adventures for technical and material support of fieldwork.

Constructive comments provided by J. H. Geisler and one anonymous reviewer improved upon our initial effort. J. Repetski helped with final checks. M. Silcox and S. Hageman guided this paper through the publication process for the Journal of Paleontology; thank you.

SJG received funding from the Citizens of Calvert County, Maryland, the Board of Calvert County Commissioners, and the Clarissa and Lincoln Dryden Endowment for Paleontology at the Calvert Marine Museum.

Accessibility of supplemental data

Supplemental data deposited in Dryad data package: http://datadryad.org/handle/10.5061/dryad.d6jk5

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Figure 0

Figure 1Partial skull of Agorophius pygmaeus. Type specimen. Plate of Phocodon holmesii Agassiz, reproduced and edited in Adobe Photoshop® from True (1907): (1) right lateral view; (2) left lateral view; (3) dorsal view; (4, 5, 6) single tooth in medial, lateral, and posterior views respectively. The scale is based on the “greatest breadth” of the skull given by True (1907) as 7.5 in. Unfortunately, that dimension does not proportionately correspond to the maximum length of the skull given as 14.5 in. The greatest breadth dimension was chosen to calibrate the scale in this image because based on what is preserved that dimension could not be any larger, whereas some of the original measured length of the skull could have been lost prior to this illustration having been made. Scale bar represents 10 cm.

Figure 1

Figure 2Partial skull of Agorophius pygmaeus, ChM PV4256, The Charleston Museum, Charleston, South Carolina: (1) left lateral view; (2) dorsal view; (3) posterior (occipital) view; (4) ventral view of left maxilla showing posterior-most alveoli (anterior to the left). Scale bar represents 10 cm.

Figure 2

Figure 3Partial skull of Agorophius pygmaeus, SC 2015.51.1a & b: (1) left facial/supraorbital region in dorsal view; (2) cerebral moiety in dorsal view; (3, 4) interpretive illustrations based on (1) and (2). (5) Line drawing to show how the two parts of the skull in (1) and (2) overlap. Scale bar represents 10 cm for (1) and (2).

Figure 3

Figure 4Partial skull of Agorophius pygmaeus. SC 2015.51.1a & b: (1) left facial/supraorbital region in left lateral view; (2) left facial/supraorbital region in ventral view; (3) cerebral moiety in ventral view; (4) posterior (occipital) view; (5) cerebral moiety in right lateral view. Skull lightly coated with sublimed ammonium chloride. Scale bar represents 10 cm.

Figure 4

Figure 5Restoration of the skull of Agorophius pygmaeus based on SC 2015.51.1 and ChM PV 4256.

Figure 5

Figure 6Left periotic of Agorophius pygmaeus. SC 2015.51.1a: (1) periotic in situ in ventral view; (2, 3) stereo pairs of the left periotic. Scale bar for (1) represents 10 mm.

Figure 6

Figure 7Partial right periotic of Agorophius pygmaeus. SC 2015.51.1c: (1) ventral view; (2) medial view; (3) dorsomedial view; (4) dorsal view. Scale bar represents 10 mm.

Figure 7

Figure 8Cladogram of relationships of Neoceti, with a focus on the basal relationships among Odontoceti. Specimens included in Agorophius pygmaeus are shown in the box outlined with dotted lines. Several clades are identified with circles, including: Ag, Agorophiidae; Ba, Balaenopteroidea; De, Delphinidae; Eo, Eomysticetidae; In, Iniidae; Li, Lipotidae; Ph, Physeteroidea; Pl, Platanistoidea; Xe, Xenorophidae; Zi, Ziphiidae.