Phocoenidae, Gray, 1825

Boessenecker, Robert W., 2013, A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, part II: Pinnipeds and Cetaceans, Geodiversitas 35 (4), pp. 815-940 : 888-889

Phocoenidae gen. et sp. indet.

REFERRED MATERIAL. — UCMP 219176, an isolated left tympanic bulla collected by R. W. Boessenecker from UCMP locality V99847 .

STRATIGRAPHIC OCCURRENCE. — Middle part of the San Gregorio section of the Purisima Formation, Early-Late Pliocene (3.35-2.5 Ma; Piacenzian-Gelasian equivalent; Fig. 2 ).

DESCRIPTION

Ŋe tympanic bulla is small ( Table 12 ), and rectangular in dorsal aspect ( Fig. 39A, D, H ). UCMP 219176 has a small, equidimensional and pachyostotic posterior processes, with slightly convex and nearly smooth posterior bullar facet with faint lon- gitudinal striations. Ŋe inner and outer posterior prominences are similar in transverse width, but the outer posterior prominence is positioned slightly further posterior to the inner posterior prominence ( Fig. 39H ). Ŋe involucrum of UCMP 219176 is gracile and lacks a strongly inflated anterior portion. In dorsal aspect, the inner posterior prominence of UCMP 219174 forms a more acute angle at its apex than in 219176. Although the outer lip is damaged, a slight inflection at the margin of the broken portion suggests it had a lateral furrow.

REMARKS AND COMPARISONS

UCMP 219176 exhibits one synapomorphy of Delphinida , an anteriorly inflated involucrum ( Muizon 1988a). Furthermore, this specimen exhibits two phocoenid synapomorphies: a short posterior process with a smooth articular surface ( Muizon 1984), and a pachyostotic posterior process ( Muizon 1988a). Ŋis specimen differs from Albireo whistleri in its smaller size, lacking a transversely massive involucrum with a convex medial margin in dorsal view, and exhibiting an outer posterior prominence that extends further posteriorly than the inner posterior prominence. UCMP 219176 differs from Delphinidae gen. et sp. indet. (UCMP 219174) described above in exhibiting a ventral crest on the medial lobe that extends further anteriorly, and in having a larger posterior process with a smooth posterior bullar facet; in UCMP 219174, the facet is more strongly striated. Ŋis specimen is identical to extant phocoenids and an undescribed fossil phocoenid (SDNHM 65276) from the San Diego Formation ( Racicot et al. 2007; this taxon is equivalent to Phocoenidae unnamed genus 2 described below), and may be synonymous with any of the other phocoenids reported herein.

Figures

FIG. 2. — Stratigraphy of the Purisima Formation: A, Stratigraphic column of the San Gregorio section of the Purisima Formation (in meters), showing stratigraphic position of UCMP vertebrate localities, dated ash beds, diatom floras, and species of Carcharodon; thickness measurements start over above missing section in uppermost part due lack of overlapping strata; epoch and stage boundaries marked as "?" are estimated; modified from Boessenecker (2011a); Pliocene-Pleistocene boundary after Hilgen et al. (2012); B, photograph of 3-4 m thick ash within Purisima Formation at mouth of San Gregorio Creek correlated with 2.5 Ma Ishi Tuff (Powell et al.2007); C, trace fossils in pervasively bioturbated sandstone,Purisima Formation,mouth of San Gregorio Creek; D, swaley cross-stratified sandstone, mouth of San Gregorio Creek. Abbreviations: Qt, Pleistocene terrace deposits; Tp, Purisima Formation; C, claystone; St, siltstone; Ss, sandstone. Scale bars: A, 2 m; B, C, 10 cm.

FIG. 39. — Tympanic bullae of delphinoid odontocetes; A, UCMP 219176, Phocoenidae gen. et sp. indet. in dorsal view; B, UCMP 219174,Delphinidae gen.et sp.indet.in dorsal view;C, UCMP 219034, cf. Globicephalinae gen. et sp. indet. in dorsal view; D, UCMP 219176 in medial view; E, UCMP 219174 in medial view; F, UCMP 219034 in medial view; H, UCMP 219176 in ventral view; I, UCMP 219174 in ventral view; J, UCMP 219034 in ventral view; K, comparison of interpretive line drawings of extant delphinids; specimen numbers for extant specimens are as follows: Globicephala macrorhynchus Gray, 1846, CAS 16466; Grampus griseus Cuvier, 1812, CAS 13461; Orcinus orca Linnaeus, 1758, CAS 23814; Pseudorca crassidens Owen, 1846, AMNH 18965; Tursiops truncatus Gray, 1866, CAS 16183). Scale bars: 3 cm.