A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.

<h4>Background</h4>A number of aberrant walruses (Odobenidae) have been described from the Neogene of the North Pacific, including specialized suction-feeding and generalist fish-eating taxa. At least one of these fossil walruses has been hypothesized to have been a specialized predator...

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Autores principales:	Robert W Boessenecker, Morgan Churchill
Formato:	article
Lenguaje:	EN
Publicado:	Public Library of Science (PLoS) 2013
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/f0c196f03ed94487b8f45a2463d19b77
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spelling	oai:doaj.org-article:f0c196f03ed94487b8f45a2463d19b772021-11-18T08:01:10ZA reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.1932-620310.1371/journal.pone.0054311https://doaj.org/article/f0c196f03ed94487b8f45a2463d19b772013-01-01T00:00:00Zhttps://www.ncbi.nlm.nih.gov/pmc/articles/pmid/23342129/?tool=EBIhttps://doaj.org/toc/1932-6203<h4>Background</h4>A number of aberrant walruses (Odobenidae) have been described from the Neogene of the North Pacific, including specialized suction-feeding and generalist fish-eating taxa. At least one of these fossil walruses has been hypothesized to have been a specialized predator of other marine mammals, the middle Miocene walrus Pelagiarctos thomasi from the Sharktooth Hill Bonebed of California (16.1-14.5 Ma).<h4>Methodology/principal findings</h4>A new specimen of Pelagiarctos from the middle Miocene "Topanga" Formation of southern California (17.5-15 Ma) allows a reassessment of the morphology and feeding ecology of this extinct walrus. The mandibles of this new specimen are robust with large canines, bulbous premolars with prominent paraconid, metaconid, hypoconid cusps, crenulated lingual cingula with small talonid basins, M₂ present, double-rooted P₃-M₁, single-rooted P₁ and M₂, and a P₂ with a bilobate root. Because this specimen lacks a fused mandibular symphysis like Pelagiarctos thomasi, it is instead referred to Pelagiarctos sp. This specimen is more informative than the fragmentary holotype of Pelagiarctos thomasi, permitting Pelagiarctos to be included within a phylogenetic analysis for the first time. Analysis of a matrix composed of 90 cranial, dental, mandibular and postcranial characters indicates that Pelagiarctos is an early diverging walrus and sister to the late Miocene walrus Imagotaria downsi. We reevaluate the evidence for a macropredatory lifestyle for Pelagiarctos, and we find no evidence of specialization towards a macrophagous diet, suggesting that Pelagiarctos was a generalist feeder with the ability to feed on large prey.<h4>Conclusions/significance</h4>This new specimen of Pelagiarctos adds to the knowledge of this problematic taxon. The phylogenetic analysis conclusively demonstrates that Pelagiarctos is an early diverging walrus. Pelagiarctos does not show morphological specializations associated with macrophagy, and was likely a generalist predator, feeding on fish, invertebrates, and the occasional warm-blooded prey item.Robert W BoesseneckerMorgan ChurchillPublic Library of Science (PLoS)articleMedicineRScienceQENPLoS ONE, Vol 8, Iss 1, p e54311 (2013)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q Robert W Boessenecker Morgan Churchill A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.
description	<h4>Background</h4>A number of aberrant walruses (Odobenidae) have been described from the Neogene of the North Pacific, including specialized suction-feeding and generalist fish-eating taxa. At least one of these fossil walruses has been hypothesized to have been a specialized predator of other marine mammals, the middle Miocene walrus Pelagiarctos thomasi from the Sharktooth Hill Bonebed of California (16.1-14.5 Ma).<h4>Methodology/principal findings</h4>A new specimen of Pelagiarctos from the middle Miocene "Topanga" Formation of southern California (17.5-15 Ma) allows a reassessment of the morphology and feeding ecology of this extinct walrus. The mandibles of this new specimen are robust with large canines, bulbous premolars with prominent paraconid, metaconid, hypoconid cusps, crenulated lingual cingula with small talonid basins, M₂ present, double-rooted P₃-M₁, single-rooted P₁ and M₂, and a P₂ with a bilobate root. Because this specimen lacks a fused mandibular symphysis like Pelagiarctos thomasi, it is instead referred to Pelagiarctos sp. This specimen is more informative than the fragmentary holotype of Pelagiarctos thomasi, permitting Pelagiarctos to be included within a phylogenetic analysis for the first time. Analysis of a matrix composed of 90 cranial, dental, mandibular and postcranial characters indicates that Pelagiarctos is an early diverging walrus and sister to the late Miocene walrus Imagotaria downsi. We reevaluate the evidence for a macropredatory lifestyle for Pelagiarctos, and we find no evidence of specialization towards a macrophagous diet, suggesting that Pelagiarctos was a generalist feeder with the ability to feed on large prey.<h4>Conclusions/significance</h4>This new specimen of Pelagiarctos adds to the knowledge of this problematic taxon. The phylogenetic analysis conclusively demonstrates that Pelagiarctos is an early diverging walrus. Pelagiarctos does not show morphological specializations associated with macrophagy, and was likely a generalist predator, feeding on fish, invertebrates, and the occasional warm-blooded prey item.
format	article
author	Robert W Boessenecker Morgan Churchill
author_facet	Robert W Boessenecker Morgan Churchill
author_sort	Robert W Boessenecker
title	A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.
title_short	A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.
title_full	A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.
title_fullStr	A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.
title_full_unstemmed	A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.
title_sort	reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus pelagiarctos.
publisher	Public Library of Science (PLoS)
publishDate	2013
url	https://doaj.org/article/f0c196f03ed94487b8f45a2463d19b77
work_keys_str_mv	AT robertwboessenecker areevaluationofthemorphologypaleoecologyandphylogeneticrelationshipsoftheenigmaticwalruspelagiarctos AT morganchurchill areevaluationofthemorphologypaleoecologyandphylogeneticrelationshipsoftheenigmaticwalruspelagiarctos AT robertwboessenecker reevaluationofthemorphologypaleoecologyandphylogeneticrelationshipsoftheenigmaticwalruspelagiarctos AT morganchurchill reevaluationofthemorphologypaleoecologyandphylogeneticrelationshipsoftheenigmaticwalruspelagiarctos
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A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.

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