Pleistocene survival of an archaic dwarf baleen whale (Mysticeti: Cetotheriidae)

Abstract

Pliocene baleen whale assemblages are characterized by a mix of early records of extant mysticetes, extinct genera within modern families, and late surviving members of the extinct family Cetotheriidae. Although Pleistocene baleen whales are poorly known, thus far they include only fossils of extant genera, indicating late Pliocene extinctions of numerous mysticetes alongside other marine mammals. Here, a new fossil of the late Neogene cetotheriid mysticete Herpetocetus is reported from the Lower to Middle Pleistocene Falor Formation of Northern California. This find demonstrates that at least one archaic mysticete survived well into the Quaternary Period, indicating a recent loss of a unique niche and a more complex pattern of Plio-Pleistocene faunal overturn for marine mammals than has been previously acknowledged. This discovery also lends indirect support to the hypothesis that the pygmy right whale (Caperea marginata) is an extant cetotheriid, as it documents another cetotheriid nearly surviving to modern times.

Independent evolution of baleen whale gigantism linked to Plio-Pleistocene ocean dynamics

“…Our estimated timing for the origin of gigantism is coincident with a decline in global mysticete diversity from 3 Ma [14] that is driven dominantly by the near extinction of the diminutive Cetotheriidae [66], and of small, ram-feeding right whales (Balaenidae). Although intensified, wind-driven upwelling seasonally increases productivity and prey densities, the effects are localized to continental shelf breaks.…”

The Pliocene marine megafauna extinction and its impact on functional diversity

“…Individual examples of faunal turnover and extinctions of large marine vertebrates (collectively known as 'marine megafauna', which includes, but is not limited to marine mammals, seabirds, turtles, sharks and rays [10][11] ) have been observed around this period. These include a substantial drop in cetacean [12][13][14] (but see 15 ) and penguin diversity [16][17] , the extinction of dugongids in the Western Atlantic and Mediterranean regions [18][19][20] , the loss of the largest shark that ever lived (Carcharocles megalodon) [21][22] , as well as extinctions of sea turtles (e.g. Psephophorus, a leatherback turtle) 23 .…”

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

“…The combination of the bilobate morphology of the bulla and dorsal margin of the involucrum running anteroventrally at one third anteroposterior length and forming a flattened area posterior to the musculotubal canal differs from all Balaenoptera spp. The size of the bulla, deep lateral furrow, and lack of a broad median furrow differ from the cetotheriid Herpetocetus, which has been reported from the coeval Falor Formation further north in Humboldt County, California (Boessenecker, 2013b). The posterior process in VMW-27 and Eschrichtius robustus potentially exhibits a hitherto unrecognized autapomorphy for the genus.…”

“…Pliocene marine mammal assemblages of California are well sampled if incompletely recorded by publications (Boessenecker, 2013a) and the absence of Eschrichtius in Pliocene strata in this region appears to be genuine. The Pliocene marine mammal assemblage of the eastern North Pacific is distinct from the extant fauna (Boessenecker, 2013a(Boessenecker, , 2013b and differs in retaining a number of archaic genera (Albireo, Balaenula, Herpetocetus, "Megaptera" miocaena), records of genera separated geographically or climatologically from extant relatives (Parapontoporia, Valenictus, and unnamed monodontids), and early records of recent genera (Balaenoptera, Callorhinus, Eubalaena, Hydrodamalis). Late Pleistocene marine mammal assemblages appear to be composed nearly entirely of extant genera and species, indicating a period of faunal turnover during the latest Pliocene or Early Pleistocene (Boessenecker, 2011(Boessenecker, , 2013a(Boessenecker, , 2013b.…”

“…The Pliocene marine mammal assemblage of the eastern North Pacific is distinct from the extant fauna (Boessenecker, 2013a(Boessenecker, , 2013b and differs in retaining a number of archaic genera (Albireo, Balaenula, Herpetocetus, "Megaptera" miocaena), records of genera separated geographically or climatologically from extant relatives (Parapontoporia, Valenictus, and unnamed monodontids), and early records of recent genera (Balaenoptera, Callorhinus, Eubalaena, Hydrodamalis). Late Pleistocene marine mammal assemblages appear to be composed nearly entirely of extant genera and species, indicating a period of faunal turnover during the latest Pliocene or Early Pleistocene (Boessenecker, 2011(Boessenecker, , 2013a(Boessenecker, , 2013b. Eschrichtius appears in the western North Pacific during the Pliocene (Ichishima et al, 2006), when Eschrichtius fossils appear to be genuinely absent from the strange Pliocene fauna of the eastern North Pacific.…”