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A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia

Abstract

Modern pinnipeds (seals, sea lions and the walrus) are semi-aquatic, generally marine carnivores the limbs of which have been modified into flippers. Recent phylogenetic studies using morphological and molecular evidence support pinniped monophyly, and suggest a sister relationship with ursoids1,2 (for example bears) or musteloids3,4,5,6,7 (the clade that includes skunks, badgers, weasels and otters). Although the position of pinnipeds within modern carnivores appears moderately well resolved, fossil evidence of the morphological steps leading from a terrestrial ancestor to the modern marine forms has been weak or contentious. The earliest well-represented fossil pinniped is Enaliarctos, a marine form with flippers, which had appeared on the northwestern shores of North America by the early Miocene epoch8,9. Here we report the discovery of a nearly complete skeleton of a new semi-aquatic carnivore from an early Miocene lake deposit in Nunavut, Canada, that represents a morphological link in early pinniped evolution. The new taxon retains a long tail and the proportions of its fore- and hindlimbs are more similar to those of modern terrestrial carnivores than to modern pinnipeds. Morphological traits indicative of semi-aquatic adaptation include a forelimb with a prominent deltopectoral ridge on the humerus, a posterodorsally expanded scapula, a pelvis with relatively short ilium, a shortened femur and flattened phalanges, suggestive of webbing. The new fossil shows evidence of pinniped affinities and similarities to the early Oligocene Amphicticeps from Asia and the late Oligocene and Miocene Potamotherium from Europe. The discovery suggests that the evolution of pinnipeds included a freshwater transitional phase, and may support the hypothesis that the Arctic was an early centre of pinniped evolution.

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Figure 1: Geographic location of fossil site.
Figure 2: Puijila darwini skeleton (NUFV 405, holotype).
Figure 3: Puijila darwini skull (NUFV 405, holotype).
Figure 4: Phylogenetic position of Puijila within Arctoidea.

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Acknowledgements

NUFV 405 was prepared by M. A. Gilbert and A. Tabrum. M. A. Gilbert prepared Figs 3 and 4 and provided specimen photographs for skeletal reconstruction (Fig. 2). Figs 1 and 2 were prepared by M. A. Klingler with contributions from N.R., A. Tirabasso and M. A. Gilbert for Fig. 2. Surface scanning data (for example for Fig. 3) was collected by P. Bloskie. T. M. Ryan and A. Walker provided the computerized tomography of the basicranium of Puijila, B. Engesser lent specimens of Potamotherium, P. D. Gingerich provided information on limb measurements, and J. R. Wible provided discussion on ear regions and commented on the manuscript. This research was supported by a palaeontology permit from the Government of Nunavut, Department of Culture, Language, Elders and Youth (D. R. Stenton, J. Ross) and with the permission of the Qikiqtani Inuit Association, especially Grise Fiord. Guidance on Inuktitut words was given by S. Nattaq and S. Mike. J. Tungilik and T. Akulukjuk provided advice on pronunciation. Field research was supported by the Canadian Museum of Nature and the Carnegie Museum of Natural History. Collections support was provided by K. Shepherd and M. Feuerstack. Logistic and other support was provided by the Polar Continental Shelf Program (B. Hyrcyk, M. Bergmann, B. Hough, T. McConaghy, M. Kristjanson and the rest of the PCSP team) and the pilots of Kenn Borek Airlines. Student travel support was provided by the Northern Scientific Training Program (Canada). Our thanks are extended to our field crew members, M. A. Gilbert, J. C. Gosse, W. T. Mitchell, M. E. Lipman and especially E. M. Ross, who found the first bones of Puijila.

Author Contributions N.R. was field leader and was responsible for phylogenetic analysis and postcranial study; M.R.D. was responsible for craniodental anatomical description and systematic study; R.H.T. was responsible for phylogeny and palaeogeography.

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Correspondence to Natalia Rybczynski.

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Rybczynski, N., Dawson, M. & Tedford, R. A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia. Nature 458, 1021–1024 (2009). https://doi.org/10.1038/nature07985

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