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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 strict consensus tree of equally weighted analysis of Archaeodobenus akamatsui and the Odobenidae, with Bremer support at nodes.
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pone.0131856.g012: The strict consensus tree of equally weighted analysis of Archaeodobenus akamatsui and the Odobenidae, with Bremer support at nodes.

Mentions: Our analysis resulted in 63 most parsimonious trees with 280 steps. The variations among the 63 trees are represented by differences in branching patterns among outgroup taxa and also ingroup taxa (mostly “dusignathines”) within the later diverging odobenids (see a strict consensus tree in Fig 12). Phylogenetic analysis revealed that the new fossil is recognized as an independent linage. The new fossil is distinguished from such earlier diverging odobenids as Prototaria spp, Proneotherium repenningi, Kamtschatarctos sinelnikovae, Neotherium mirum and Pseudotaria muramotoi in having two unequivocal and equivocal synapomorphies with later diverging odobenids such as the pentagonal basioccipital (Character 30) and straight dorsal margin of the spinous process of the axis (Character 91) respectively. However, the new fossil lacks synapomorphies of later diverging odobenids (i.e., Imagotaria downsi, Pontolis magnus, the “dusignathines” and the Odobeninae) such as the presence of ventral tuberosity of the zygomatic root of the maxilla (Character 7), shallow glenoid fossa (Character 26), large mastoid process of the squamosal (Character 33), absence of the metaconid on the lower cheek teeth (Character 70) and double rooted upper P3 roots (Character 74). Although not included within the computer-based phylogenetic analyses, Pelagiarctos thomasi and P. sp. of Boessenecker and Churchill [13] are clearly distinguishable from the new fossil by their very large size and robustness and by having extremely large cheek teeth. Therefore, the new fossil is differentiated from all previously known taxa within the Odobenidae. In addition, the new fossil has autapomorphic characters such as sharply divergent mandibular arch (Character 44) and slightly concave talonid basin of the lower cheek teeth (Character 69).


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 strict consensus tree of equally weighted analysis of Archaeodobenus akamatsui and the Odobenidae, with Bremer support at nodes.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0131856.g012: The strict consensus tree of equally weighted analysis of Archaeodobenus akamatsui and the Odobenidae, with Bremer support at nodes.
Mentions: Our analysis resulted in 63 most parsimonious trees with 280 steps. The variations among the 63 trees are represented by differences in branching patterns among outgroup taxa and also ingroup taxa (mostly “dusignathines”) within the later diverging odobenids (see a strict consensus tree in Fig 12). Phylogenetic analysis revealed that the new fossil is recognized as an independent linage. The new fossil is distinguished from such earlier diverging odobenids as Prototaria spp, Proneotherium repenningi, Kamtschatarctos sinelnikovae, Neotherium mirum and Pseudotaria muramotoi in having two unequivocal and equivocal synapomorphies with later diverging odobenids such as the pentagonal basioccipital (Character 30) and straight dorsal margin of the spinous process of the axis (Character 91) respectively. However, the new fossil lacks synapomorphies of later diverging odobenids (i.e., Imagotaria downsi, Pontolis magnus, the “dusignathines” and the Odobeninae) such as the presence of ventral tuberosity of the zygomatic root of the maxilla (Character 7), shallow glenoid fossa (Character 26), large mastoid process of the squamosal (Character 33), absence of the metaconid on the lower cheek teeth (Character 70) and double rooted upper P3 roots (Character 74). Although not included within the computer-based phylogenetic analyses, Pelagiarctos thomasi and P. sp. of Boessenecker and Churchill [13] are clearly distinguishable from the new fossil by their very large size and robustness and by having extremely large cheek teeth. Therefore, the new fossil is differentiated from all previously known taxa within the Odobenidae. In addition, the new fossil has autapomorphic characters such as sharply divergent mandibular arch (Character 44) and slightly concave talonid basin of the lower cheek teeth (Character 69).

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