New Miocene fossil Allodelphinidae (Cetacea, Odontoceti, Platanistoidea) from the North Pacific Ocean

Species in the extinct platanistoid family Allodelphinidae are dolphin-like odontocete (echolocating) cetaceans known by fossils from early and middle Miocene marine deposits around the eastern and western margins of the North Pacific Ocean. Allodelphinids were relatively large animals, having estimated adult total body lengths of approximately 3 to 5 meters, a long rostrum, the mandible extending to the end of the rostrum with a fused mandibular symphysis, large and anteroposteriorly elongated cervical vertebrae, and elongated humerus. The previously named allodelphinid species, all from California, are early Miocene Allodelphis pratti Wilson, 1935, and A. woodburnei Barnes and Reynolds, 2009, and middle Miocene Zarhinocetus errabundus (Kellogg, 1931). Additional new species belonging in the family are Goedertius oregonensis Barnes and Kimura, new genus and new species, from the early Miocene Nye Mudstone in Lincoln County, Oregon, U.S.A.; Ninjadelphis ujiharai Kimura, new genus and new species, from the early Miocene Awa Group in Mie Prefecture, Japan; and Zarhinocetus donnamatsonae Barnes, new species, from the late early Miocene to early middle Miocene Astoria Formation in Grays Harbor Country, Washington State, U.S.A. Goedertius oregonensis is more derived than the species of Allodelphis. Ninjadelphis ujiharai is more derived than Goedertius oregonensis and has anteriorly retracted posterior ends of its premaxillae. Species of Zarhinocetus Barnes and Reynolds, 2009, have a maxillary tuberosity on each side of the base of the rostrum and a maxillary crest over the orbit. Zarhinocetus donnamatsonae is more derived than N. ujiharai, but more primitive than Zarhinocetus errabundus, which is the most derived species in the family. Contrary to the general evolutionary trend in cetaceans, allodelphinids evolved secondarily enlarged and anteroposteriorly elongated cervical vertebrae, and all cervical vertebrae remained un-fused to one another. Their elongated necks, combined with a large occipital shield and thick nuchal crest on the cranium, indicate that allodelphinids had well-developed muscles for movements of the head. Their extremely long and slender rostra may have allowed either raptorial or benthic feeding, and niche partitioning can explain the diversity that is now being documented within the family. Their swimming methods likely favored maneuverability but not speed.