Morphobank

Project 530: R. W. Boessenecker, M. Churchill. 2013. A Reevaluation of the Morphology, Paleoecology, and Phylogenetic Relationships of the Enigmatic Walrus Pelagiarctos. PLOS ONE. 8 (1):e54311.

Specimen: † Pelagiarctos sp. Barnes, 1988 (SDNHM/uncatalogued)

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Abstract

Background
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).
Methodology/Principal Findings
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.
Conclusions/Significance
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.

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Project DOI: 10.7934/P530, http://dx.doi.org/10.7934/P530

This project contains	Matrices
624 Media 2 Matrices 1 Document 27 Taxa 36 Specimens 90 Characters Total size of project's media files: 1.18G Download Project SDD File	Total scored cells: 2432 Total media associated with cells: 581 Total labels associated with cell media: 556
	Characters
	Total characters: 129 Total characters with associated media: 0 Total characters with media with labels: 0 Total character states: 249 Total character states with associated media: 79 Total character states with media with labels:78 Total unordered/ordered characters:129/0

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MorphoBank Project 530

Creation Date:
12 June 2011
Publication Date:
16 January 2013
Project views: 233411
Media downloads: 55
Matrix downloads: 72

This research
supported by

Authors' Institutions

University of Otago

University of Wyoming

Members

Morgan Churchill
Project Administrator

527

2026
(2026, 0, 0)

223

200

Robert Boessenecker
Full membership

156

406
(406, 0, 0)

358

356

Taxonomic Overview for Matrix 'M1174' (20 Taxa)

taxon	unscored cells	scored cells	no cell support	NPA cells	"-" cells	cell images	labels on cell images	member access
[1] † Enaliarctos emlongi Taxon name last Modified on 12/05/13	0	39	7	0	0	31	24	2
[2] † Pteronarctos goedertae Taxon name last Modified on 12/05/13	0	39	11	0	0	27	27	2
[3] † Desmatophoca oregonensis Taxon name last Modified on 12/05/13	0	39	5	0	0	33	31	2
[4] † Allodesmus gracilis Taxon name last Modified on 12/05/13	0	39	12	0	0	27	26	2
[5] Monachus monachus Taxon name last Modified on 12/05/13	0	39	4	0	0	35	33	2
[6] Erignathus barbatus Taxon name last Modified on 12/05/13	0	41	6	0	0	33	31	2
[7] Callorhinus ursinus Taxon name last Modified on 12/05/13	1	38	6	0	0	32	30	2
[8] † Proneotherium repenningi Taxon name last Modified on 12/05/13	0	39	6	0	0	37	36	2
[9] † Kamtschatarctos sinelnikovae Taxon name last Modified on 12/05/13	9	30	5	0	0	25	24	2
[10] † Neotherium mirum Taxon name last Modified on 12/05/13	0	39	31	0	0	6	6	2
[11] † Imagotaria downsi Taxon name last Modified on 12/05/13	0	44	4	0	0	58	56	2
[12] † Pelagiarctos sp. Taxon name last Modified on 12/05/13	5	34	2	0	0	33	33	2
[13] † Pontolis magnus Taxon name last Modified on 12/05/13	1	38	37	0	0	0	0	2
[14] † Gomphotaria pugnax Taxon name last Modified on 12/05/13	5	34	4	0	0	28	28	2
[15] † Dusignathus santacruzensis Taxon name last Modified on 12/05/13	0	39	4	0	0	34	37	2
[16] † Dusignathus seftoni Taxon name last Modified on 12/05/13	7	33	5	0	0	25	25	2
[17] † Protodobenus japonicus Taxon name last Modified on 12/05/13	1	38	3	0	0	33	31	2
[18] † Ontocetus emmonsi Taxon name last Modified on 12/05/13	1	38	3	0	0	37	37	2
[19] † Valenictus chulavistensis Taxon name last Modified on 12/05/13	19	20	6	0	0	14	13	2
[20] Odobenus rosmarus Taxon name last Modified on 12/05/13	2	37	4	0	0	33	28	2

Taxonomic Overview for Matrix 'M1891' (23 Taxa)

taxon	unscored cells	scored cells	no cell support	NPA cells	"-" cells	cell images	labels on cell images	member access
[1] † Enaliarctos emlongi Taxon name last Modified on 12/05/13	8	82	80	0	0	0	0	2
[2] † Pteronarctos goedertae Taxon name last Modified on 12/05/13	8	82	81	0	0	0	0	2
[3] Callorhinus ursinus Taxon name last Modified on 12/05/13	1	89	89	0	0	0	0	2
[4] † Desmatophoca oregonensis Taxon name last Modified on 12/05/13	6	86	83	0	0	0	0	2
[5] † Allodesmus gracilis Taxon name last Modified on 12/05/13	0	92	90	0	0	0	0	2
[6] Erignathus barbatus Taxon name last Modified on 12/05/13	0	92	90	0	0	0	0	2
[7] Monachus monachus Taxon name last Modified on 12/05/13	0	90	90	0	0	0	0	2
[8] † Prototaria primigenia Taxon name last Modified on 12/05/13	47	43	43	0	0	0	0	2
[9] † Proneotherium repenningi Taxon name last Modified on 12/05/13	8	82	81	0	0	0	0	2
[10] † Neotherium mirum Taxon name last Modified on 12/05/13	1	89	87	0	0	0	0	2
[11] † Kamtschatarctos sinelnikovae Taxon name last Modified on 12/05/13	49	41	40	0	0	0	0	2
[12] † Pseudotaria muramotoi Taxon name last Modified on 12/05/13	54	36	36	0	0	0	0	2
[13] † Imagotaria downsi Taxon name last Modified on 12/05/13	1	96	88	0	0	0	0	2
[14] † Pelagiarctos sp. Taxon name last Modified on 12/05/13	56	34	33	0	0	0	0	2
[15] † Pontolis magnus Taxon name last Modified on 12/05/13	3	87	86	0	0	0	0	2
[16] † Dusignathus santacruzensis Taxon name last Modified on 12/05/13	35	55	53	0	0	0	0	2
[17] † Dusignathus seftoni Taxon name last Modified on 12/05/13	16	76	70	0	0	0	0	2
[18] † Gomphotaria pugnax Taxon name last Modified on 12/05/13	13	77	74	0	0	0	0	2
[19] Aivukus cedrosensis Taxon name last Modified on 12/05/13	32	58	58	0	0	0	0	2
[20] † Protodobenus japonicus Taxon name last Modified on 12/05/13	26	64	61	0	0	0	0	2
[21] † Ontocetus emmonsi Taxon name last Modified on 12/05/13	2	88	87	0	0	0	0	2
[22] † Valenictus chulavistensis Taxon name last Modified on 12/05/13	22	68	68	0	0	0	0	2
[23] Odobenus rosmarus Taxon name last Modified on 12/05/13	2	88	88	0	0	0	0	2

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Specimen list	39034
Documents list	2466
Taxon list	18856
Bibliography	6107

Project downloads

type	number of downloads	Individual items downloaded (where applicable)
Total downloads from project	540
Matrix downloads	72	Kohno 2006 modified matrix (41 downloads); walrus mandible and lower dentition (31 downloads);
Project downloads	404
Document downloads	9	(9 downloads);
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