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. (SDNHM/uncatalogued)

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 containsMatrices
  • 624 Media
  • 2 Matrices
  • 1 Document
  • 27 Taxa
  • 36 Specimens
  • 90 Characters
Total size of project's media files: 1513 MB

Download Project SDD File
Total scored cells: 2432
Total media associated with cells: 688
Total labels associated with cell media: 738
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:79
Total unordered/ordered characters:129/0
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MorphoBank Project 530

    This research
    supported by

    Authors' Institutions

    • University of Otago

    • University of Wyoming



    Members

    member name taxa specimens media chars character
    media
    labels
    cell scorings
    (scored, NPA, "-")
    cell
    medialabels
    rules
    Morgan Churchill
    Project Administrator
    Last logged in 01/16/13
    2424527957202026
    (2026, 0, 0)
    2552180
    Robert Boessenecker
    Full membership
    Last logged in 11/07/12
    312973488156406
    (406, 0, 0)
    4334290


    Taxonomic Overview for Matrix 'M1174' (20 Taxa)

    taxon unscored
    cells
    scored
    cells
    no cell
    support
    NPA
    cells
    "-" cellscell images labels on
    cell images
    member
    access
    [1] † Enaliarctos emlongi
    Last Modified in 12/05/13
    03970037282
    [2] † Pteronarctos goedertae
    Last Modified in 12/05/13
    039110035342
    [3] † Desmatophoca oregonensis
    Last Modified in 12/05/13
    03950033312
    [4] † Allodesmus gracilis
    Last Modified in 12/05/13
    039120027262
    [5] Monachus monachus
    Last Modified in 12/05/13
    03940035332
    [6] Erignathus barbatus
    Last Modified in 12/05/13
    04160033312
    [7] Callorhinus ursinus
    Last Modified in 12/05/13
    13860032302
    [8] † Proneotherium repenningi
    Last Modified in 12/05/13
    03960049472
    [9] † Kamtschatarctos sinelnikovae
    Last Modified in 12/05/13
    93050034322
    [10] † Neotherium mirum
    Last Modified in 12/05/13
    0393100872
    [11] † Imagotaria downsi
    Last Modified in 12/05/13
    04440065622
    [12] † Pelagiarctos sp.
    Last Modified in 12/05/13
    53420040382
    [13] † Pontolis magnus
    Last Modified in 12/05/13
    1383700102
    [14] † Gomphotaria pugnax
    Last Modified in 12/05/13
    53440034332
    [15] † Dusignathus santacruzensis
    Last Modified in 12/05/13
    03940045462
    [16] † Dusignathus seftoni
    Last Modified in 12/05/13
    73350036352
    [17] † Protodobenus japonicus
    Last Modified in 12/05/13
    13830043402
    [18] † Ontocetus emmonsi
    Last Modified in 12/05/13
    13830046452
    [19] † Valenictus chulavistensis
    Last Modified in 12/05/13
    192060017162
    [20] Odobenus rosmarus
    Last Modified in 12/05/13
    23740038332


    Taxonomic Overview for Matrix 'M1891' (23 Taxa)

    taxon unscored
    cells
    scored
    cells
    no cell
    support
    NPA
    cells
    "-" cellscell images labels on
    cell images
    member
    access
    [1] † Enaliarctos emlongi
    Last Modified in 12/05/13
    8828000002
    [2] † Pteronarctos goedertae
    Last Modified in 12/05/13
    8828100002
    [3] Callorhinus ursinus
    Last Modified in 12/05/13
    1898900002
    [4] † Desmatophoca oregonensis
    Last Modified in 12/05/13
    6868300002
    [5] † Allodesmus gracilis
    Last Modified in 12/05/13
    0929000002
    [6] Erignathus barbatus
    Last Modified in 12/05/13
    0929000002
    [7] Monachus monachus
    Last Modified in 12/05/13
    0909000002
    [8] † Prototaria primigenia
    Last Modified in 12/05/13
    47434300002
    [9] † Proneotherium repenningi
    Last Modified in 12/05/13
    8828100002
    [10] † Neotherium mirum
    Last Modified in 12/05/13
    1898700002
    [11] † Kamtschatarctos sinelnikovae
    Last Modified in 12/05/13
    49414000002
    [12] † Pseudotaria muramotoi
    Last Modified in 12/05/13
    54363600002
    [13] † Imagotaria downsi
    Last Modified in 12/05/13
    1968800002
    [14] † Pelagiarctos sp.
    Last Modified in 12/05/13
    56343300002
    [15] † Pontolis magnus
    Last Modified in 12/05/13
    3878600002
    [16] † Dusignathus santacruzensis
    Last Modified in 12/05/13
    35555300002
    [17] † Dusignathus seftoni
    Last Modified in 12/05/13
    16767000002
    [18] † Gomphotaria pugnax
    Last Modified in 12/05/13
    13777400002
    [19] Aivukus cedrosensis
    Last Modified in 12/05/13
    32585800002
    [20] † Protodobenus japonicus
    Last Modified in 12/05/13
    26646100002
    [21] † Ontocetus emmonsi
    Last Modified in 12/05/13
    2888700002
    [22] † Valenictus chulavistensis
    Last Modified in 12/05/13
    22686800002
    [23] Odobenus rosmarus
    Last Modified in 12/05/13
    2888800002


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