Monday, March 9, 2020

[PaleoMammalogy • 2020] Corumictis wolsani • The Earliest Mustelid (Carnivora, Mustelidae) in North America

Corumictis wolsani  Paterson

in Paterson, Samuels, Rybczynski, et al., 2020. 
Illustration: Henry Sharpe 

Until now, the pre-Miocene fossil record of mustelids in North America has been restricted to specimens attributable to oligobunine taxa and isolated remains tentatively allocated to the genus Plesictis. In the present study, we report on a nearly complete cranium and a referred dentary of a new genus and species of mustelid. The specimens were recovered from the Turtle Cove and Kimberly Members of the John Day Formation, Oregon, USA.

These excellently preserved specimens more confidently confirm the presence of mustelids in the Early and Late Oligocene (Early and Late Arikareean) of North America. Like the holotype specimen of ‘Plesictisjulieni, the new species lacks an alisphenoid canal and a postprotocrista on the M1 (synapomorphies of Mustelidae), but retains a dorsally deep suprameatal fossa (a feature occasionally suggested to be unique to Procyonidae). Phylogenetic analyses, applying parsimony and Bayesian inference to combined molecular (five genes totalling 5490 bp) and morphological data, recover this new species of mustelid as sister-species to ‘Plesictisjulieni. The results of these analyses reveal that the new genus is a close relative of other species of Plesictis and several taxa traditionally allied with Oligobuninae, thereby rendering Oligobuninae paraphyletic. We further discuss the significance of the relatively small size of this new mustelid as it relates to predictions based on increased aridification of the palaeoclimate and the expansion of open habitats in the Oligocene.

Systematic palaeontology

Class Mammalia Linnaeus, 1758
Order Carnivora Bowditch, 1821
Suborder Caniformia Kretzoi, 1943

Infraorder Arctoidea Flower, 1869
Order-Group Taxon Mustelida Tedford, 1976

Family Mustelidae Fischer, 1817

Genus Corumictis Paterson, gen. nov.

Type species: Corumictis wolsani Paterson

Included species: Corumictis julieni (Viret, 1929), comb. nov. (Basionym: Plesictis julieni Viret, 1929;
Corumictis wolsani, sp. nov. (described below).

Distribution: Early and Late Oligocene (Early and Late Arikareean, Ar1–Ar3) of Oregon, USA; Early Miocene (MN 2a) of France.

Etymology: From the Latin ad Corum, north-west, referring to the dispersal of mustelids to and from the north-western portion of North America, and the Greek ικτις, ictis, a weasel-like carnivorous animal.

Holotype skull of Corumictis wolsani (JODA 8167) in: A, dorsal; B, lateral; C, ventral views.

Scale bar equals 1 cm. 

ALF = anterior lacerate foramen, MP = mastoid process, NF = nasolabialis fossa, NS = nasal sinuses, OpF = optic foramen, OrF = orbital fissure, SuO = supraorbital processes, TC = temporal crests.

Holotype skull of Corumictis wolsani (JODA 8167) 

Corumictis wolsani Paterson, sp. nov.

Etymology: The epithet is a patronym for Mieczysław Wolsan, who has extensively studied fossil musteloids and worked to reveal their evolutionary history.

Ryan Paterson, Joshua X. Samuels, Natalia Rybczynski, Michael J. Ryan and Hillary C. Maddin. 2020. The Earliest Mustelid in North America. Zoological Journal of the Linnean Society. zlz091. DOI:  10.1093/zoolinnean/zlz091

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