About 10 million years ago on the shores of what ’s now Hokkaido , Japan , ancient sea horse congeneric sported sharp eye tooth but no tusks , harmonize to findings published inPLOS ONEthis hebdomad .
now , walruses ( Odobenus rosmarus ) are the only living members of the family Odobenidae , but the group was incredibly diverse in the past times : The fossils of at least 16 genera and 20 species of extinct sea horse have already been recovered . Most of them endure during the recent Miocene and the Pliocene , about 8 million to 2 million years ago . A few twelvemonth ago , a staff member of the Tobetsu Town Board of Education discovered the partial skeleton of a fossil pinniped ( seals , ocean lions , and friends ) in the later Miocene Ichibangawa Formation near the Rutaka Bridge in northern Japan . The left cranium , jawbones , vertebra and ribs , and some branch clappers were in a sandstone block that at some point in all likelihood floated downstream from Aoyama dam about 1.5 kilometer to the N .
harmonize toUniversity of Otago ’s Yoshihiro Tanakaand colleagues , the fossilized cadaver belong to a never - before - see archaic odobenid with a slight , small cranium and non - tusked , temperate - sized upper canine tooth . While they were n’t ivory - like , they were large , sharp , and cone shape - mold , assess 86.3 millimeters long ( or nearly 3.5 inches ) . They name it Archaeodobenus akamatsui from the Greek “ archaios ” meaning ancient . The species name honor Morio Akamatsu , conservator emeritus of the Hokkaido Museum .
The holotype braincase of Archaeodobenus akamatsui . Tanaka Y , Kohno N / PLOS ONE .
Archaeodobenus akamatsuilived 10 million to 9.5 million age ago . Based on its relatively large canines and the well - developed crown on the back of the skull , the specimen was likely a male ; his cranial sutures indicate that he was young , a subadult . The turgid mammalian would have been between 2.8 and 3 meter long ( that ’s nearly 10 feet ) , and it weighed anywhere between 390 and 473 kilograms ( 860 to 1,042 pounds ) .
A belated Miocene odobenid discover in 2006 namedPseudotaria muramotoilived around the same time in this same location . But it had unlike gaunt characteristic . base on a phyletic depth psychology , the two species rive during the later Miocene in the westerly North Pacific . This speedy diversification of antediluvian odobenids was probable the result of geologic isolation among their extinct plebeian ancestor . In the beginning of the early late Miocene , 12.5 million to 10.5 million year ago , the ocean point was drop as ledge complex body part start to develop .
tooth of Archaeodobenus akamatsui . Tanaka Y , Kohno N / PLOS ONE .
