Cheng-Hsiu Tsai and Robert W. Boessenecker (2015). An Early Pleistocene gray whale (Cetacea: Eschrichtiidae)
from the Rio Dell Formation of northern California. Journal of Paleontology, 89, pp 103-109 doi:10.1017/jpa.2014.9
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 extant Eschrichtius robustus and differs from Pliocene Eschrichtius
sp. 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 fossil Eschrichtius in 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.
Regards and all the best,
Tsai