CETACEA BRISSON, 1762

Charles L. Powell, Ii, Clites, Erica C. & Poust, Ashley W., 2019, Miocene marine macropaleontology of the fourth bore Caldecott Tunnel excavation, Berkeley Hills, Oakland, California, USA, PaleoBios 36, pp. 1-34 : 19-20

CETACEA BRISSON, 1762

ODONTOCETI FLOWER, 1867

FIGS. 35, 36

Cetacean remains recovered from the Caldecott Tunnel Tsm unit include a partial premaxilla (UCMP 269020) among other less identifiable fragments. The descriptive anatomical terminology used here follows Mead and Fordyce (2009). UCMP 269020 is a left mid-premaxilla of a medium-sized odontocete cetacean. T-shaped in cross-section, it has a sharp lateral edge which would have been flush with the maxilla and a more rounded medial border where it would have met the opposing right premaxilla in life. The ventral process is crushed and less distinguishable from the surrounding matrix, but does expand ventrally where the palatine surface would be visible in ventral view. The porcelanous part is gently convex. The labial surface, anterolateral sulcus, and any branches of the infraorbital canal are not visible, suggesting that this fragment is from the anterior half of the rostral portion. The convex rostral surface is 32.3 mm wide and the height from the palatine surface of the premaxilla is 32.5 mm. The entire fragment is 80 mm long.

The identification of UCMP 269020 as an odontocete is a strong stratigraphic indicator that the rocks of the western portal of the Caldecott Tunnel are Neogene in age and that the tunnel does not include any of the unnamed Cretaceous Cenomanian/Turonian sedimentary rocks present further west along Highway 24. Though many cetaceans are well known from the Oligocene of North America, including the oldest Odontocetes (Uhen 2010), their diversity is not high until the Miocene. Of the odontocete cetaceans known from the West Coast, several possess premaxillae with convex dorsal surfaces and without further morphology a generic assignment is not warranted. The specimen is relatively large: significantly bigger than Pliocene delphinids from the Purisima Formation, similar or slightly smaller than Physeteroids from the Round Mountain Silt (UCMP collections) and larger than Kampholophos which has a 26 mm wide premaxilla (Rensberger 1969).

Figures

Figure 36. Odontocete premaxilla, lateral view of hypotype, UCMP 269020.