HERPETOCETINAE

Robert, Boessenecker, W. & Mt, 2011, Herpetocetine (Cetacea: Mysticeti) dentaries from the Upper Miocene Santa Margarita Sandstone of Central California, PaleoBios 30 (1), pp. 1-12 : 3-5

SUBFAMILY: HERPETOCETINAE Steeman 2007 SUBFAMILY: HERPETOCETINAE genus et species indeterminate

Referred Specimens— UCMP 85431 , partial skeleton including complete right dentary and associated forelimb elements and vertebrae, collected August 8, 1968, by R. Bowman and L.G. Barnes, and UCMP 85429 , nearly complete right dentary missing only the mandibular condyle and angular process, collected 1969 by C.A. Repenning . UCMP 85429 is slightly smaller than UCMP 85431 . These dentaries are morphologically identical and share a characteristic anteroposteriorly elongate, laterally projecting coronoid process and an anterior extension of the mandibular foramen opening (see below). A third dentary from the same locality ( UCMP 85430 ) is missing the diagnostic posterior-most portion. The horizontal ramus is morphologically identical, though smaller in absolute size compared to UCMP 85429 , and may also be referable to this unidentified herpetocetine taxon .

Locality —UCMP V6857, Taylor Quarry, uppermost Santa Margarita Sandstone, Santa Cruz County, California. Detailed locality information available on request to qualified researchers.

Description— This description of UCMP 85431 and 85429 is restricted to mandibular morphology because vertebrae and ribs are generally not diagnostic in cetaceans ( Deméré et al. 2005, Barnes 1976) and beyond the scope of this study. The description of the posterior portion of the dentary is based on UCMP 85431 ( Figs. 3–5), while that of the anterior portion of the dentary is based on both

Carnivora

Desmatophocidae

Allodesmus sp. ( Repenning and Tedford 1977)

Odobenidae

Imagotaria downsi ( Repenning and Tedford 1977, Barnes 1971)

“ Desmatophocine” sp. A ( Barnes 1972)

Otariidae

Pithanotaria starri ( Repenning and Tedford 1977)

Cetacea

Odontoceti

Delphinidae

Delphinidae indet. ( Domning 1978)

“ Kentriodontidae ”

Liolithax sp. ( Barnes 1978)

Monodontidae

Delphinapterinae indet. ( Barnes 1976)

Allodelphinidae

Zarhinocetus errabundus ( Domning 1978)

Physeteridae

Physeteridae indet. ( Domning 1978)

Mysticeti

Cetotheriidae

Nannocetus eremus ( Whitmore and Barnes 2008)

Herpetocetinae genus and species indet. (this study)

Balaenopteridae

Balaenopteridae indet. ( Domning 1978)

“ Megaptera ” miocaena (Boessenecker unpublished data) Desmostylia

Desmostylidae

Desmostylus sp. ( Barnes 1978)

Paleoparadoxiidae

Paleoparadoxia sp. ( Mitchell and Repenning 1963)

Sirenia

Dugongidae

Dusisiren jordani ( Domning 1978)

Proboscidea

Gomphotheriidae

Gomphotherium sp. ( Clark 1981)

Perissodactyla

Equidae

Archaeohippus cf. mourningi ( Clark 1981)

Hipparion cf. forcei ( Clark 1981)

Cormohipparion occidentale ( Clark 1981)

Pliohippus sp. ( Clark 1981)

Artiodactyla

Camelidae

Camelidae indet. ( Clark 1981)

specimens ( Figs. 3–8). In dorsal aspect the dentary is slightly bowed laterally, and less laterally bowed than most extant balaenopterids. The medial surface is slightly convex, while the lateral surface is strongly convex, in contrast to extant Balaenoptera ( Deméré 1986) . Anteriorly, the cross sectional shape of the dentary progressively increases in dorsoventral diameter and narrows transversely. In addition, the anterior third of the dentary is also longitudinally rotated so that the medial surface of the dentary faces dorso-medially rather than medially like the posterior two thirds; among extant mysticetes, this feature is unique to balaenopterids ( Deméré 1986). The dentary of UCMP 85431 is slightly larger in overall size than UCMP 85429 ( Table 2).

On the medial surface of the anteriormost portion of the horizontal ramus, a faint ridge defines the symphyseal groove, which extends for the anterior 1/6 of the dentary. Fourteen anteriorly oriented gingival foramina are arrayed along the dorsolateral surface of the dentary, laterally adjacent to a blunt crest that runs longitudinally along the entire dorsal surface. These foramina are anteroposteriorly short posteriorly, and increase in length toward the anterior extremity of the dentary. The anteriormost gingival foramen in UCMP 85429 (and UCMP 85430) occurs nearly at the anterior apex of the horizontal ramus, but lies ventral to the other foramina, and is instead manifested on the lateral surface as a large and anteroposteriorly short foramen; this feature is present but damaged in UCMP 85431.

In UCMP 85429, a series of six anteriorly oriented foramina occur on the dorsal surface, medially adjacent to the dorsal crest, anterior to the coronoid process, and posterior to the posterior-most gingival foramen. This dorsal crest merges posteriorly with the coronoid process, which is damaged in UCMP 85431, but intact in UCMP 85429. In the latter, the coronoid process is an elongate, broadly triangular crest that projects laterally at the apex. The medial surface of the horizontal ramus at the position of the coronoid process is planar, vertically oriented, and merges dorsally with the medially positioned coronoid process. Lateral and adjacent to the coronoid process, a shallow fossa occurs on the dorsal surface of the ramus. The posterior coronoid crest is a small ridge that descends from the coronoid process to form the medial edge of a thin, flat shelf that overhangs the mandibular foramen dorsally. The anterior portion of this ridge projects medially. This feature was termed the inward elevation by Kimura (2002) and was postulated to serve as the attachment for the frontomandibular stay in balaenopterids ( Lambertsen et al. 1995). A small ridge extends posterolaterally from the coronoid crest to merge with the anterodorsal margin of the mandibular condyle. The anteriorly V-shaped anterior margin of the mandibular foramen is located below the coronoid process in both UCMP 85431 and 85429 ( Figs. 4, 7). The mandibular foramen opens posteriorly into a well-defined cylindrical mandibular fossa, demarcated laterally by the mandibular condyle and a slight ridge medially that forms the bony margin of the mandibular foramen anteriorly. In cross section, the widened portion of the mandibular foramen extends further anteriorly in the horizontal ramus than the coronoid process.

The mandibular condyle is antero-posteriorly elongate, with a flattened articular surface that is D-shaped in posterior view. The condyle is slightly disc-shaped, with a planar medial margin, and a convex lateral margin. The condyle is offset laterally from the ramus. The articular surface of the condyle is oriented approximately 45 º from the horizontal plane when viewed in lateral or medial aspect ( Figs. 4, 5, 10, 12). A shallow notch occurs at the medial base of the coronoid process at the site of the internal pterygoid muscle insertion ( Bouetel and Muizon 2006, Kellogg 1968). The angular process is small, and posteroventrally projects to form a flat shelf posterior to the mandibular condyle. The posterior end of the angular process is round in dorsal and lateral aspect. Figures 9–11 show a reconstruction of the complete dentary, based on UCMP 85431 and 85429.