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A New Late Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan Suggests Rapid Diversification of Basal Miocene Odobenids.

Tanaka Y, Kohno N - PLoS ONE (2015)

Bottom Line: A new genus and species of archaic odobenid, Archaeodobenus akamatsui, gen. et sp. nov. from the late Miocene (ca. 10.0-9.5 Ma) top of the Ichibangawa Formation, Hokkaido, northern Japan, suggests rapid diversification of basal Miocene walruses.Archaeodobenus akamatsui is the contemporaneous Pseudotaria muramotoi from the same formation, but they are distinguishable from each other in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and other postcranial features.Based on our phylogenetic analysis, A. akamatsui might have split from P. muramotoi at the late Miocene in the western North Pacific.

View Article: PubMed Central - PubMed

Affiliation: Hokkaido University Museum, Kita 8 Nishi 5, Kita-ku, Sapporo, Hokkaido, 060-0808, Japan; Department of Geology, University of Otago, 360 Leith walk, PO Box 56, Dunedin, 9054, New Zealand; Numata Fossil Museum, 2-7-49, 1 Minami, Numata Town, Hokkaido, 078-2202, Japan.

ABSTRACT
The modern walrus, Odobenus rosmarus, is specialized and only extant member of the family Odobenidae. They were much more diversified in the past, and at least 16 genera and 20 species of fossil walruses have been known. Although their diversity increased in the late Miocene and Pliocene (around 8-2 Million years ago), older records are poorly known. A new genus and species of archaic odobenid, Archaeodobenus akamatsui, gen. et sp. nov. from the late Miocene (ca. 10.0-9.5 Ma) top of the Ichibangawa Formation, Hokkaido, northern Japan, suggests rapid diversification of basal Miocene walruses. Archaeodobenus akamatsui is the contemporaneous Pseudotaria muramotoi from the same formation, but they are distinguishable from each other in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and other postcranial features. Based on our phylogenetic analysis, A. akamatsui might have split from P. muramotoi at the late Miocene in the western North Pacific. This rapid diversification of the archaic odobenids occurred with a combination of marine regression and transgression, which provided geological isolation among the common ancestors of extinct odobenids.

No MeSH data available.


Related in: MedlinePlus

The atlas and axis of Archaeodobenus akamatsui and Pseudotaria muramotoi.(A)—(D) Archaeodobenus akamatsui, (E)—(H) Pseudotaria muramotoi, (A) and (E) anterior view of the atlas, (B) and (F) left lateral view of the atlas, (C) and (G) anterior view of the axis, (D) and (H) left lateral view of the axis.
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pone.0131856.g009: The atlas and axis of Archaeodobenus akamatsui and Pseudotaria muramotoi.(A)—(D) Archaeodobenus akamatsui, (E)—(H) Pseudotaria muramotoi, (A) and (E) anterior view of the atlas, (B) and (F) left lateral view of the atlas, (C) and (G) anterior view of the axis, (D) and (H) left lateral view of the axis.

Mentions: Archaeodobenus akamatsui gen. et sp. nov. is presently known only from the holotype, which is from the top of the Ichibangawa Formation as described above. The same formation has also produced another odobenid Pseudotaria muramotoi Kohno, 2006. Therefore, both species are sympatric at least geochronologically. These two species of fossil odobenids are closely related to each other based on the phylogenetic analysis, but are not monophyletic. Indeed, the basioccipital in A. akamatsui is pentagonal in shape as a derived condition of all the later diverging odobenids, but the same portion in P. muramotoi is primitively parallel sided as in earlier diverging odobenids as well as the late Oligocene and early Miocene pinnipedimorphs. In addition, the mastoid process is small in A. akamatsui among the Odobenidae, but is stronger in comparison with the sister P. muramotoi. Also, the preserved cervicals in this new taxon show morphological differences between them (Fig 9). For example, the blade-like dorsal margin of the spinous process of the axis (Character 91) in A. akamatsui is recognized as a derived condition that unites this taxon with later diverging odobenids such as the modern walrus, Odobenus rosmarus and the Pliocene extinct walrus, Valenictus chulavistensis (SDSNH 36786: San Diego Natural History Museum) of the subfamily Odobeninae as the potential synapomorphy for all the later diverging odobenids such as Imagotaria, Pontolis and “dusignathines” as well as the monophyletic odobenines.


A New Late Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan Suggests Rapid Diversification of Basal Miocene Odobenids.

Tanaka Y, Kohno N - PLoS ONE (2015)

The atlas and axis of Archaeodobenus akamatsui and Pseudotaria muramotoi.(A)—(D) Archaeodobenus akamatsui, (E)—(H) Pseudotaria muramotoi, (A) and (E) anterior view of the atlas, (B) and (F) left lateral view of the atlas, (C) and (G) anterior view of the axis, (D) and (H) left lateral view of the axis.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4526471&req=5

pone.0131856.g009: The atlas and axis of Archaeodobenus akamatsui and Pseudotaria muramotoi.(A)—(D) Archaeodobenus akamatsui, (E)—(H) Pseudotaria muramotoi, (A) and (E) anterior view of the atlas, (B) and (F) left lateral view of the atlas, (C) and (G) anterior view of the axis, (D) and (H) left lateral view of the axis.
Mentions: Archaeodobenus akamatsui gen. et sp. nov. is presently known only from the holotype, which is from the top of the Ichibangawa Formation as described above. The same formation has also produced another odobenid Pseudotaria muramotoi Kohno, 2006. Therefore, both species are sympatric at least geochronologically. These two species of fossil odobenids are closely related to each other based on the phylogenetic analysis, but are not monophyletic. Indeed, the basioccipital in A. akamatsui is pentagonal in shape as a derived condition of all the later diverging odobenids, but the same portion in P. muramotoi is primitively parallel sided as in earlier diverging odobenids as well as the late Oligocene and early Miocene pinnipedimorphs. In addition, the mastoid process is small in A. akamatsui among the Odobenidae, but is stronger in comparison with the sister P. muramotoi. Also, the preserved cervicals in this new taxon show morphological differences between them (Fig 9). For example, the blade-like dorsal margin of the spinous process of the axis (Character 91) in A. akamatsui is recognized as a derived condition that unites this taxon with later diverging odobenids such as the modern walrus, Odobenus rosmarus and the Pliocene extinct walrus, Valenictus chulavistensis (SDSNH 36786: San Diego Natural History Museum) of the subfamily Odobeninae as the potential synapomorphy for all the later diverging odobenids such as Imagotaria, Pontolis and “dusignathines” as well as the monophyletic odobenines.

Bottom Line: A new genus and species of archaic odobenid, Archaeodobenus akamatsui, gen. et sp. nov. from the late Miocene (ca. 10.0-9.5 Ma) top of the Ichibangawa Formation, Hokkaido, northern Japan, suggests rapid diversification of basal Miocene walruses.Archaeodobenus akamatsui is the contemporaneous Pseudotaria muramotoi from the same formation, but they are distinguishable from each other in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and other postcranial features.Based on our phylogenetic analysis, A. akamatsui might have split from P. muramotoi at the late Miocene in the western North Pacific.

View Article: PubMed Central - PubMed

Affiliation: Hokkaido University Museum, Kita 8 Nishi 5, Kita-ku, Sapporo, Hokkaido, 060-0808, Japan; Department of Geology, University of Otago, 360 Leith walk, PO Box 56, Dunedin, 9054, New Zealand; Numata Fossil Museum, 2-7-49, 1 Minami, Numata Town, Hokkaido, 078-2202, Japan.

ABSTRACT
The modern walrus, Odobenus rosmarus, is specialized and only extant member of the family Odobenidae. They were much more diversified in the past, and at least 16 genera and 20 species of fossil walruses have been known. Although their diversity increased in the late Miocene and Pliocene (around 8-2 Million years ago), older records are poorly known. A new genus and species of archaic odobenid, Archaeodobenus akamatsui, gen. et sp. nov. from the late Miocene (ca. 10.0-9.5 Ma) top of the Ichibangawa Formation, Hokkaido, northern Japan, suggests rapid diversification of basal Miocene walruses. Archaeodobenus akamatsui is the contemporaneous Pseudotaria muramotoi from the same formation, but they are distinguishable from each other in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and other postcranial features. Based on our phylogenetic analysis, A. akamatsui might have split from P. muramotoi at the late Miocene in the western North Pacific. This rapid diversification of the archaic odobenids occurred with a combination of marine regression and transgression, which provided geological isolation among the common ancestors of extinct odobenids.

No MeSH data available.


Related in: MedlinePlus