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| Pangurban egiae Poust, Barrett & Tomiya, 2022 |
Abstract
Carnivoraforms (crown carnivorans and their closest relatives) first occupied hypercarnivorous niches near the dawn of the late Eocene, 40–37 Ma. This followed the decline or extinction of earlier carnivorous groups, Mesonychia and Oxyaenodonta, leaving carnivoraforms and hyaenodontan meat-eaters as high trophic level consumers. The pattern of this change and the relative contributions of the taxonomic groups has hitherto been unclear. We report a new genus and species of the sabretoothed mammalian carnivore family Nimravidae, Pangurban egiae, from the Eocene Pomerado Conglomerate of southern California, with strongly derived hypercarnivorous features. While geochronologically the oldest named nimravid in North America, Pangurban egiae is recovered as phylogenetically derived, with affinities to Hoplophoneus. This provides unequivocal evidence for rapid radiation and spread of nimravid carnivores across Asia and North America and constrains the timing of early divergences within the family. Pangurban egiae narrows the gap between convergent iterations of sabretoothed mammalian carnivores and demonstrates swift diversification of the hypercarnivorous nimravids during a period of global climatic instability. Furthermore, it highlights the top-to-bottom restructuring North American ecosystems underwent during the Eocene–Oligocene transition, resulting in carnivoraforms taking positions as trophic specialists for the first time, a niche they still occupy today.
Keywords: evolution, sabretooth, Hoplophoneus, Eocene–Oligocene biotic transition, Duchesnean, carnassial
Systematic palaeontology
Class MAMMALIA sensu Rowe [1988]
unranked clade CARNIVORAMORPHA sensu Bryant [1996] (amended from Wyss & Flynn [1993])
unranked clade CARNIVORAFORMES Flynn, Finarelli & Spaulding [2010]
Family NIMRAVIDAE sensu Bryant [1996]
Pangurban egiae gen. et sp. nov.
Type locality and horizon. SDSNH Locality 4042 (Spring Canyon Site 2). Upper member of Pomerado Conglomerate, San Diego, CA, USA, here considered middle to late Duchesnean in age (ca 40–37 Ma; see electronic supplementary material, text).
Diagnosis. Anterior cutting edge of P4 expressed as sharp and distinct preparacristal blade, not reaching apex of paracone; anterior face of P4 flattened and nearly vertical giving the paracone a steep angle. Differs from: Maofelis and MA-PHQ 348 (undet. nimravid specimen housed at Muséum d'Histoire Naturelle Victor Brun, Montauban, France) in infraorbital foramen posterior to P3, double-rooted P3, P3 width to length ratio 0.4–0.65; Maofelis, MA-PHQ 348, and ‘nimravines’ of which includes barbourofelins, in reduced or absent P4 protocone, P4 metastylar blade length to paracone length ratio of 1.0–1.3, P3 crown height 48–70% that of P4; hoplophoneins (Hoplophoneus, Eusmilus and Nanosmilus) in the absence of parastyle on P4.
Etymology. The generic name is from the Old Irish, in reference to the cat in the 9th century CE poem of the same name, whose hunting is likened to the academic pursuit of truth. The species name honours the contribution of palaeontologist Naoko Egi to the study of terrestrial carnivore evolution on both sides of the northern Pacific Ocean, mirroring the nimravid distribution.
Ashley W. Poust, Paul Z. Barrett and Susumu Tomiya. 2022. An early Nimravid from California and the Rise of Hypercarnivorous Mammals after the middle Eocene Climatic Optimum. Biol. Lett.18; 20220291. DOI: 10.1098/rsbl.2022.0291
新種の化石肉食哺乳類の発見
An early nimravid from California and the rise of hypercarnivorous mammals after the Middle Eocene Climatic Optimum
