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.
Highlights
The almost six-fold increase of characters primarily to regions much, if not entirely, neglected by prior studies produced extremely disparate topologies compared to those studies
One of the major results of this analysis was the recovery of a basal split dividing nimravid evolution along two paths
All well-represented Eocene-Miocene nimravid taxa (34 taxa), the new taxon and four outgroups were coded for 225 morphological characters, some of which are autapomorphic (Supplementary Information) from direct observations of specimens, or from literature as listed in Supplementary Table 1
Summary
ZooBank LSID (for nomenclatural act): AE752634-8697-473C-8CD6-CA301A8E56A8 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 p ublication[4,16,17,18,19,20]. 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 Referred material Paratype: USNM 18214, cranium, Supplementary Fig. S1. Locality and horizon Orellan of Wyoming (White River Fm., Brule Mbr.), Niobrara County, USA
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