Allodesmus, KELLOGG, 1922

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

CF. ALLODESMUS KELLOGG, 1922

UCMP 270043 is a very cracked and shattered fragment of a proximal rib preserved in dark, hard, indurated shale. The specimen nonetheless preserves a morphology resembling the proximal ribs of the contemporaneous Allodesmus . Comparison with specimens of marine mammals in the UCMP collections suggests that UCMP 270043 is similar to the proximal portions of Allodesmus ribs in size, width to height ratio, and the presence of a relatively wide proximal costal groove.

The middle Miocene was a time of marked phylogenetic diversity within pinnipedimorpha, including imagotariine walruses, members of Desmatophocidae including Allodesmus , some of the first phocid and otariid relatives, and even relict “enaliarctines” ( Berta et al. 2018, Poust and Boessenecker 2018). Thus, the possible presence of two size classes of pinnipedimorphs within the same formation is not surprising, especially if the presence of numerous fossil fish is indicative of a nutrient-rich environment.