Eubalaena Gray 1864
Creators: name: Boessenecker, Robert W.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Cetacea
Balaenidae
Eubalaena

description: cf. Eubalaena sp. 1
REFERRED MATERIAL. — UCMP 219100, a small partial right tympanic bulla; and UCMP 219481, a small partial right tympanic bulla. Collected by R.W. Boessenecker from UCMP locality V99851.
STRATIGRAPHIC OCCURRENCE. — Lowermost part of the San Gregorio section of the Purisima Formation, latest Miocene (6.4-5.6 Ma, Messinian equivalent; Fig. 2).
DESCRIPTION
Except where noted, this description is based primarily on UCMP 219100. Ŋis tympanic bulla has a large involucrum with a greatly expanded medial surface which is anteriorly truncated (Fig. 10 A-C). Several elongate, deep, and anterolaterally directed transverse creases occur on the involucrum. Posteriorly, the involucrum is much deeper dorsoventrally. A deep sulcus runs adjacent to the involucral ridge; the involucral ridge is slightly retracted from the ventral margin, and diverges posteriorly from the main ridge. Ŋe ventral surface is relatively smooth and convex and lacks a keel-like main ridge. Laterally adjacent to the main ridge there is an indistinct
involucrum
longitudinal furrow. Ŋe posteromedial portion of the bulla is rather robust and inflated in medial aspect. A fragment of the anterior portion of the outer lip is present, and it is broadly convex in anterior view. Ŋis results in a eustachian opening that is narrow; anteriorly this margin is slit-like and has an angle of c. 45° (between the involucrum and outer lip). UCMP 219481 also exhibits a narrow eustachian opening, although it has an anteroventral corner of the eustachian opening that is more acutely defined and not broadly curved as in UCMP 219100 (Fig. 10F).
REMARKS AND COMPARISONS
Ŋese tympanic bullae share many features with extant Eubalaena Gray, 1864, including an elevated anterior lobe and a narrow eustachian opening (Ekdale et al. 2011). Nevertheless, the involucral and main ridges are posteriorly divergent, whereas in extant Eubalaena they are parallel. Ŋey differ from balaenopterids in having a convex dorsal margin of the involucrum in medial and lateral aspect; balaenopterid bullae generally differ from those of extant balaenids in having a relatively straight medial margin of the involucrum that is not broadly arched in dorsal view (Oishi & Hasegawa 1995b; Ekdale et al. 2011). Ŋese bullae differ from Balaena Linnaeus, 1758 in being relatively transversely broader; bullae of extant Balaena are transversely flattened relative to those of Eubalaena (Ekdale et al. 2011). Ŋe tympanic bulla of Caperea Gray, 1864 is similar in size, but transversely narrower than UCMP 219100; it exhibits a posteroventrally expanded involucrum and a rectangular eustachian opening, unlike UCMP 219100 and 219481 (Ekdale et al. 2011). UCMP 219100 differs from Balaenella Bisconti, 2005 in having a rounded anteroventral margin that is not shaped into a corner (Bisconti 2005), although this is seen in UCMP 219481 and Eubalaena. UCMP 219100 and 219481 differ from the tympanic bulla of B. balaenopsis Van Beneden, 1872 in exhibiting a narrow, triangular eustachian opening; UCMP 219100 further differs in exhibiting a more transversely inflated bulla, and UCMP 219481 differs in exhibiting a corner-like anteroventral margin. Ŋe tympanic bulla of Bal-
aenula astensis Trevisan, 1942 is more transversely compressed than UCMP 219100, and exhibits a eustachian opening that is less acutely triangular and slit-like than UCMP 219100 and 219481, although it is somewhat narrower than the broadly rounded eustachian opening in B. balaenopsis. A balaenid tympanic bulla (UCMP 29852; identified as Balaenula sp. by Barnes 1977) from the Purisima Formation at Point Reyes (Early Pliocene) is similar in size, but appears to be transversely thinner and exhibits a flatter medial surface of the involucrum relative to UCMP 219100 and 219481. Although they are relatively small (Table 5), these specimens share enough features with Eubalaena to be tentatively identified to this genus.
description: Published as part of Boessenecker, Robert W., 2013, A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, part II: Pinnipeds and Cetaceans, pp. 815-940 in Geodiversitas 35 (4) on pages 834-836, DOI: 10.5252/g2013n4a5, http://zenodo.org/record/4538200