Nimravidae is anextinctfamily ofcarnivorans, sometimes known asfalse saber-toothed cats, whose fossils are found inNorth America,Africa, andEurasia. Not considered to belong to the true cats (familyFelidae), the nimravids are generally considered closely related and classified as a distinct family in thesuborderFeliformia.[2] The family consisted of three subfamilies hoplophonines,nimravines, andbarbourofelines. Barourofelines were initially classified as asubfamily of the Nimravidae since 1991, however in 2004, they were reassigned to their own distinct family.[3] Since 2020, the majority of experts consider barbourofelines as nimravids again.[4][2][5][6][7] Nimravids first appeared in the Middle Eocene in Asia, withMaofelis being the mostplesiomorphic taxa.[5][8] The family would go extinct around 7 Ma.[2]
The family Nimravidae was named by American paleontologistEdward Drinker Cope in 1880,[9] with the type genus asNimravus. The family was assigned to Fissipedia by Cope (1889); to Caniformia by Flynn and Galiano (1982); to Aeluroidea by Carroll (1988); to Feliformia by Bryant (1991); and to Carnivoramorpha, by Wesley-Hunt and Werdelin (2005).[10]
Nimravids are placed intribes by some authors to reflect closer relationships between genera within the family. Some nimravids evolved into large, toothed, cat-like forms with massive flattened upper canines and accompanying mandibular flanges. Some had dentition similar to felids, or modern cats, with smaller canines. Others had moderately increased canines in a more intermediate relationship between the saber-toothed cats and felids. The upper canines were not only shorter, but also more conical, than those of the true saber-toothed cats (Machairodontinae). These nimravids are referred to as "false saber-tooths". Thebarbourofelids were for a while no longer included in Nimravidae, following elevation to family as sister clade to the true cats (familyFelidae).[11][12] However, majority of recent studies have returned them to Nimravidae, with one study suggesting they are part of Nimravinae.[2][5][13][6][7]
Most nimravids had muscular, low-slung, cat-like bodies, with shorter legs and tails than are typical of cats. Unlikeextant Feliformia, the nimravids had a different bone structure in thesmall bones of the ear. Themiddle ear of true cats is housed in an external structure called anauditory bulla, which is separated by aseptum into two chambers. Nimravid remains showossified bullae with no septum, or no trace at all of the entire bulla. They are assumed to have had acartilaginous housing of the ear mechanism.[24] Nimravid feet were short, indicating they walked in aplantigrade or semiplantigrade posture, i.e., on the flat of the feet rather than the toes, like modern cats.[25]
The ancestors of nimravids and cats diverged from a common ancestor soon after theCaniformia–Feliformia split, in the middleEocene about 50 million years ago (Ma), with a minimum constraint of 43 Ma.
The global climate at this time was warm and wet, but was trending cooler and drier toward the late Eocene. The lush forests of the Eocene were transforming to scrub and open woodland. This climatic trend continued in theOligocene, and nimravids evidently flourished in this environment. North America and Asia were connected and shared much related fauna.[36] Their diversification and increase in body size coincided with the decline and extinction of theoxyaenids, which opened the cat-like carnivore niche.[37] Nimravids made their appearance in Europe within MP21 followingGrande Coupure.[38]
Barbourofelines probably evolved fromnimravines dispersing into Africa during the Oligocene. The presence of largehyaenodonts prevented them from reaching a large size but were able to carve a niche due to their dental morphology. Eventually, they dispersed from Africa into Eurasia and later into North America.[2]
Both hoplophonines and nimravines died out during the Oligocene epoch, with the last taxa going extinct 29.5 and 25.9 Ma respectively.[2] In Europe, nimravids went extinct during the early Oligocene, coinciding with increased aridity in Europe.[38] In North America, their extinction also coincided with the expansion of grasslands, in addition to competition withamphicyonids.[39][25] The extinction of North American nimravids started the infamouscat gap, a 7 million year period when no cat-like predators were present in North America.[25]
Barbourofelines went extinct during the late Miocene, around 7 Ma, for unknown reasons.[2] Antón Mauricio suggested competition withmachairodonts such asMachairodus andNimravides, may have contributed to their extinction, as barbourofelines were widely successful despite the wider expansion of grasslands.[25] However, Paul Barret has contested this hypothesis because of the limited temporal overlap between both clades.[2] In addition,Albanosmilus, the last genus to go extinct in Eurasia, was also able to coexist and compete with machairodontsAmphimachairodus andMachairodus in some localities for over a million years.[40][41][42] Other experts suggested it was more likely barbourofelines went extinct because of the faunal overturn during the Late Miocene due to the wider expansion of grasslands.[2][43][41]
^abcdBarrett, P. Z.; Hopkins, W. S. B.; Price, S. A. (2021). "How many sabertooths? Reevaluating the number of carnivoran sabertooth lineages with total-evidence Bayesian techniques and a novel origin of the Miocene Nimravidae".Journal of Vertebrate Paleontology.41 (1) e1923523.doi:10.1080/02724634.2021.1923523.S2CID236221655.
^Flynn, John J.; Galiano, Henry (1982). "Phylogeny of early Tertiary Carnivora, with a description of a new species of Protictis from the middle Eocene of Northwestern Wyoming".American Museum Novitates.hdl:2246/5338.
^Werdelin, L.; Yamaguchi, N.; Johnson, W. E. & O'Brien, S. J. (2010)."Phylogeny and evolution of cats (Felidae)". In Macdonald, D. W. & Loveridge, A. J. (eds.).Biology and Conservation of Wild Felids. Oxford, UK: Oxford University Press. pp. 59–82.ISBN978-0-19-923445-5.
^Martin, L. D. (1991, January).A new miniature saber-toothed nimravid from the Oligocene of Nebraska. InAnnales Zoologici Fennici (pp. 341-348). Finnish Zoological Publishing Board, formed by the Finnish Academy of Sciences, Societas Biologica Fennica Vanamo, Societas pro Fauna et Flora Fennica, and Societas Scientiarum Fennica.
^Antón, Mauricio (2013).Sabertooth. Bloomington, Indiana: University of Indiana Press. p. 97.ISBN978-0-253-01042-1.
^Peigne, Stéphane (May 2003). "Systematic review of European Nimravinae (Mammalia, Carnivora, Nimravidae) and the phylogenetic relationships of Palaeogene Nimravidae".Zoologica Scripta.32 (3):199–229.doi:10.1046/j.1463-6409.2003.00116.x.S2CID86827900.
^Turner, Alan (1997).The Big Cats and their Fossil Relatives: an illustrated guide. New York: Columbia University Press. p. 234.ISBN0-231-10228-3.
^Naples, V. L.; Martin, L. D. (June 2008). "Restoration of the superficial facial musculature in nimravids".Zoological Journal of the Linnean Society.130 (1):55–81.doi:10.1111/j.1096-3642.2000.tb02195.x.
^Bryant, Harold N. (1996). "Nimravidae". In Donald R. Prothero and Robert J. Emry (ed.).The Terrestrial Eocene-Oligocene Transition in North America. Cambridge, England: Cambridge University Press. p. 468.ISBN0-521-43387-8.
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