Thunnus undetermined

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 : 24

THUNNUS SP.

FIG. 42

The vertebra represented by UCMP 218506 is broken at an oblique angle, with a natural cast of the conical concave surface of the centrum preserved ( Fig. 42 , left side). The vertebral body is large with a slightly dorsally flattened outline. The septa are relatively simple but do seem to have two lateral fossae. The sides between these septa are deeply incised. The lip of the centrum is smooth and somewhat curved instead of sharp. The whole vertebra is 44 mm in length, of which the central concavities make up 20 mm on each side leaving only a very narrow bony center.

The deeply incised sides, distally wide centra, and large size indicate scombrid affinities, while the dorso- ventrally flattened shape of the centrum with a midline depression is a Thunnus synapomorphy. Thunnus is also known from the “Monterey” Formation of southern California ( David 1943). Boessenecker (2011) described a similar vertebra from the Pliocene Purisima Formation. They are also known from several sites in the Pliocene of the East Coast, including the Yorktown Formation at Lee Creek Mine, North Carolina,where tuna vertebrae are found with puncture marks from the feeding behavior of billfish (Schneider and Fierstine 2004). UCMP 218506 is similar to large vertebrae from the Round Mountain Silt (Shark Tooth Hill), Kern County, found in the UCMP collections. These elements are relatively common and in conjunction with this Claremont specimen indicate that Thunnus or a related fish was a widespread member of coastal and basinal ecosystems in California during mid-Miocene times. In spite of this, these elements are not commonly described making this specimen equal in age to the oldest published specimen of Thunnus in the eastern North Pacific.

Figures

Figure 42. Thunnus vertebra, hypotype, UCMP 218506.