Otarioid seals of the Neogene

Abstract

The otarioid seals originated in the North Pacific region and most of their history is centered in this area. They include four families: the extant Odobenidae (walruses) and Otariidae (fur seals and sea lions) and the extinct Desmatophocidae and Enaliarctidae. Early in their development, the odobenids dispersed through the Central American Seaway to the North Atlantic, where the living walrus evolved. By late Pliocene time, the odobenids had become extinct in the North Pacific but the modern walrus spread from the Atlantic to the Pacific by way of the Arctic Ocean in late Pleistocene time. The history of the odobenids is known back to the early middle Miocene, at which time they seem to have evolved out of the ancestral otarioid family, the Enaliarctidae. The odobenids were most 1 diverse in the North Pacific during the late Miocene when six genera belonging to two subfamilies are known. A new genus and species, Aiuukus cedrosensis, from the Almejas Formation of Baja California, is a privitive odobenid of the Subfamily Odobeninae. Three Pliocene and younger genera, including the living genus, are recognized in the Atlantic, but evolution in this area was essentially unidirectional toward modern walrus. The history of the otariid seals began in the late middle or early late Miocene when this family evolved out of the last ofthe Enaliarctidae. The otariids remained a family with little variety, and, relative to the odobenids, slight evolutionary change until the late Pliocene or early Pleistocene, more or less the time of extinction of the odobenids in the Pacific. During this period of little diversification, one new otariid genus, Thallassoleon, is recognized. This genus contains two new species: T. mexicanus, from the Almejas Formation of Baja California, and T. mac• nallyae, from the Drakes Bay Formation of Point Reyes, California. The otariids are today in their period of greatest diversification-there are seven living genera. By early Pliocene time, the otariids had dispersed to the South Pacific Ocean, whence during the Pleistocene, they spread to their present circumantarctic distribution. They have never reached the North Atlantic. The extinct desmatophocids evolved out of the enaliarctid group in the early Miocene and became most diverse in the middle Miocene. They are last know.n from rocks of late Miocene age, at about the time that the odobenids began to diversify. The desmatophocids seem nev~r to have left the North Pacific, but they are known from southern California to Alaska and from Japan. The Enaliarctidae were ancestral to the other three families and are largely unstudied. They were derived from primitive ursid land carnivores, presumably during the Oligocene, and may be described as flippered marine carnivores with heterodont dentition in which the premolar, carnassial, and molar teeth are differ

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

“…noted that other marine mammals including Dusisiren jordani and Imagotaria downsi had been previously reported from the same unit, which typify early Late Miocene Tortonian-equivalent marine mammal assemblages (e.g. Monterey Formation, Santa Margarita Sandstone; Repenning and Tedford 1977;Domning 1978;Barnes et al 1985). described a partial braincase of Nannocetus eremus from the uppermost Santa Margarita Sandstone in Santa Cruz County, California, which has been estimated by Repenning and Tedford (1977) to be approximately 9 Ma in age; they estimated the entire unit to be 12-9 Ma in age.…”

“…Monterey Formation, Santa Margarita Sandstone; Repenning and Tedford 1977;Domning 1978;Barnes et al 1985). described a partial braincase of Nannocetus eremus from the uppermost Santa Margarita Sandstone in Santa Cruz County, California, which has been estimated by Repenning and Tedford (1977) to be approximately 9 Ma in age; they estimated the entire unit to be 12-9 Ma in age. More recent work by Beyer et al (2009) indicates the Towsley Formation has yielded Delmontian microfossils, and is thus 7.7-5.2 Ma in age.…”

New Enaliarctos* (Pinnipedimorpha) from the Oligocene and Miocene of Oregon and the Role of "Enaliarctids" in Pinniped Phylogeny

“…Monophyly of the Otariidae (= Otariinae Mitchell, 1968Mitchell, , 1975Barnes, 1989) has fraditionally been accepted (Repenning and Tedford, 1977;Berta and Demere, 1986;Barnes, 1989). This analysis identified only a single character reversal, the presence of large shelf-like supraorbital processes as uniting otariids (SYNAPOMORPHY 7).…”

A third species ofMancallafrom the late Pliocene San Diego Formation of California (Aves : Alcidae)

“…Mancalla emlongi is an even larger and evidently much rarer contemporary of these two species. M. califomiensis and M. cedrosensis axe the size of M. diegensis and are somewhat older than the species from the San Diego Formation (see Barnes, 1973, andRepenning andTedford, 1977, for a discussion of the age of the type locality of M. cedrosensis). It remains to be determined whether either of the two earlier species is ancestral to any of those known from later deposits.…”