Delphinidae, Gray, 1821

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 : 886

Delphinidae gen. et sp. indet.

REFERRED MATERIAL. — UCMP 219174, an isolated tympanic bulla collected by R. W. Boessenecker from UCMP locality V99853 .

STRATIGRAPHIC OCCURRENCE. — Middle part of the San Gregorio section of the Purisima Formation, Early Pliocene (c. 5-3.35 Ma; Zanclean-Piacenzian equivalent; Fig. 2 ).

DESCRIPTION

Ŋis specimen is small ( Table 12 ) and rectangular in dorsal aspect ( Fig. 39B, E, I ). Ŋe posterior process is small, dorsoventrally shallow, and bears several longitudinal striations on the posterior bullar facet.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. 39I ). Ŋe involucrum of UCMP 219174 is anteriorly inflated ( Fig. 39E ). In medial aspect, the inner posterior prominence of UCMP 219174 forms an acute angle at its apex.

REMARKS AND COMPARISONS

Ŋis specimen exhibits one synapomorphy of the Delphinida , an anteriorly inflated involucrum ( Muizon 1988a). It also exhibits one delphinid synapomorphy, a ventral crest on the medial lobe that terminates posterior to the midpoint of the bulla ( Geisler & Sanders 2003). It is similar in morphology to UCMP 219034 (tentatively referred to a globicephaline below), except for its much smaller size. Ŋis specimen is generally similar to tympanic bullae of extant delphinine delphinids, and represents a single occurrence of a small-bodied delphinid in the San Gregorio assemblage.

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.