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| Eusmilus adelos Barrett, 2021 |
Abstract
Nimravids were the first carnivorans to evolve saberteeth, but previously portrayed as having a narrow evolutionary trajectory of increasing degrees of sabertooth specialization. Here I present a novel hypothesis about the evolution of this group, including a description of Eusmilus adelos, the largest known hoplophonine, which forces a re-evaluation of not only their relationships, but perceived paleoecology. Using a tip-dated Bayesian analysis with sophisticated evolutionary models, nimravids can now be viewed as following two paths of evolution: one led to numerous early dirk-tooth forms, including E. adelos, while the other converged on living feline morphology, tens of millions of years before its appearance in felids.
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| Partial skeleton of USNM 12820, Eusmilus adelos with shaded known elements. Cranial abbreviations: fr frontal, na nasal, mp mastoid process, (A) cn carnassial notch, mc main cusp of P3, pa paracone, pcc posterior cingular cusp of P3, ps parastyle; (B–D) bis brachialis insertion site, lg lateral groove of ulna, rn radial notch, sln semilunar notch, (E–G) ce capitular eminence of radius, rt radial tuberosity, (H–J) dpc delto-pectoral crest, of olecranon fossa, sc supinator crest (brachial flange), *remnants of bridge enclosing epicondylar foramen. Eusmilus adelos skeletal reconstruction by Dhruv Franklin. |
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| Tip-dated Bayesian phylogeny of the Nimravidae, outgroups (save Tapocyon) removed. Two main clades were recovered, the Hopliphoninae and Nimravinae, the latter of which includes all barbourofelin taxa. Color gradient reflects maximum-likelihood estimation of ancestral body mass. Additional nodal values (e.g., posterior probability, divergence dates) can be found in Supplementary. |
Systematic palaeontology
Carnivora
Nimravidae
Eusmilus
Eusmilus adelos sp. nov.
Holotype: Smithsonian National Museum of Natural History, Washington D.C., USA (USNM) 12820: partially crushed cranium, parts of both dentaries, atlas, axis, 3rd, 5th and 7th cervical vertebrae, three lumbar vertebrae, left: scapula, distal humerus, proximal and distal ends of radius, proximal ulna (Figs. 1, 2, 3, Supplementary Figs. S1–S3).
Etymology: From the Greek adelos, for unseen, unknown, or secret. The specific epithet refers to the unclear taxonomic affiliations these specimens have had in their more than 85 year history of publication.
Paul Zachary Barrett. 2021. The Largest Hoplophonine and A Complex New Hypothesis of Nimravid Evolution. Scientific Reports. 11, 21078. DOI: 10.1038/s41598-021-00521-1