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.