An Early Pleistocene gray whale (Cetacea: Eschrichtiidae) from the Rio Dell Formation of northern California

Abstract

The earliest fossil gray whale (Eschrichtius) from the eastern North Pacific is reported from the Lower Pleistocene Rio Dell Formation of Humboldt County, Northern California. This specimen, a tympanic bulla and posterior process, is identical in morphology to extantEschrichtius robustusand differs from PlioceneEschrichtiussp. from the western North Pacific (Japan). Thus, it suggests that the modern bulla morphology of the gray whale had been acquired by the Early Pleistocene. The absence of fossilEschrichtiusin the Pliocene of the eastern North Pacific may indicate that the extant gray whale lineage originated in the western North Pacific during the Pliocene before invading the eastern North Pacific during the Early Pleistocene. Further discoveries of Plio-Pleistocene gray whale fossils will help test this hypothesis and properly interpret the evolutionary history of eschrichtiid clade.

New fossil remains of the commensal barnacleCryptolepas rhachianectiprovide evidence of gray whales in the prehistoric South Pacific

“…Modern gray whales live in two distinct populations in the western and eastern North Pacific, although some interchange between these populations does occur (LeDuc et al, 2002; Cooke et al, 2007; IWC, 2011). While the fossil record clearly attests to the presence of the gray whale lineage in the North Pacific, there are no historical or fossil records of gray whale populations living in the equatorial Pacific or southern hemisphere (Tsai et al, 2014; Tsai and Boessenecker, 2015; Kimura et al, 2018).…”