Eubalaena

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 : 836

cf. Eubalaena sp. 2

REFERRED MATERIAL. — UCMP 219099, a partial left tympanic bulla collected by R.W. Boessenecker from UCMP locality V99846 .

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

DESCRIPTION

Ŋis larger tympanic bulla is missing most of its outer lip, and is similar in most regards to the above described specimens of cf. Eubalaena sp. 1. It differs from UCMP 219100 in its larger size and several other features; the description of this specimen follows that for cf. Eubalaena sp. 1 except for the differences outlined below. Ŋis specimen further differs from UCMP 219100 by having a much more medially convex involucrum in ventral aspect ( Fig. 10D, E ). Furthermore, it has a well-defined concave longitudinal furrow laterally adjacent to the main ridge. Ŋe main ridge also forms a welldeveloped ventral keel, and unlike UCMP 219100, the main and involucral ridges are parallel.

REMARKS AND COMPARISONS

Ŋe great dorsoventral depth and massive medial face of the involucrum identify this specimen as a balaenid ( Oishi & Hasegawa 1995b; Ekdale et al. 2011). It differs from Balaena in being transversely thicker, and shares similar large size and transverse thickness with extant Eubalaena , although it is incomplete ( Table 5 ; Ekdale et al. 2011).Ŋe much larger size and younger (Early-Late Pliocene) age of the specimen suggest it is not conspecific with UCMP 219100. Several tympanic bullae of this same size and morphology are known from the Santa Cruz section of the Purisima Formation (UCMP 29852, 167800, SCMNH 9990.07, 21654, 21658; latest Miocene-Early Pliocene, Messinian-Zanclean equivalent, 6.9-4.5 Ma).

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. 10. — Tympanic bullae of balaenid mysticetes:A, UCMP 219100,partial right tympanic bulla of cf. Eubalaena sp. 1 in medial view; B, UCMP 219100 in dorsal view; C, UCMP 219100 in ventral view; D, UCMP 219099, partial left tympanic bulla of cf. Eubalaena sp. 2 in medial view; E, UCMP 219099 in dorsal view; F, UCMP 219481, fragment of right tympanic bulla of cf. Eubalaena sp. 1 in medial view. Scale bar: 3 cm.