Nimravidae
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Nimravidae is an extinct family of carnivorans, sometimes known as false saber-toothed cats, whose fossils are found in North America, Africa, and Eurasia. Not considered to belong to the true cats (family Felidae), the nimravids are generally considered closely related and classified as a distinct family in the suborder Feliformia. Fossils have been dated from the Middle Eocene through the Late Miocene epochs (Bartonian through Messinian stages, 41.03–7 million years ago), spanning about Template:Mya.<ref name="Barrett21" />
The barbourofelines, classified as a subfamily of the Nimravidae since 1991, were reassigned to their own distinct family in 2004.<ref>Template:Cite journal</ref> However, since 2020, the majority of experts consider barbourofelines as nimravids again.<ref>Template:Cite journal</ref><ref name="Barrett21" /><ref name="Barrettetal21">Template:Cite journal</ref><ref name="Werdelin-2021">Template:Cite journal</ref><ref name="Jasinski-2022">Template:Cite journal</ref>
Taxonomy
The family Nimravidae was named by American paleontologist Edward Drinker Cope in 1880,<ref>Template:Cite journal</ref> with the type genus as Nimravus. 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).<ref>Template:Cite journal</ref>
Nimravids are placed in tribes 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". The barbourofelids were for a while no longer included in Nimravidae, following elevation to family as sister clade to the true cats (family Felidae).<ref>Template:Cite journal</ref><ref>Template:Cite book</ref> However, majority of recent studies have returned them to Nimravidae, with one study suggesting they are part of Nimravinae.<ref name="Barrett21" /><ref name="Barrettetal21" /><ref>Template:Cite journal</ref><ref name="Werdelin-2021" /><ref name="Jasinski-2022" />
Not only did nimravids exhibit diverse dentition, but they also showed the same diversity in size and morphology as cats. Nimravids such as Barbourofelis morrisi, Eusmilus sicarius, and Hoplophoneus occidentalis were leopard-sized,<ref name="Turner2">Template:Cite book</ref><ref>Template:Cite web</ref><ref name="Sabertooth">Template:Cite book</ref> while some, such as Albanosmilus jourdani and E. adelos, were the size jaguars to small lions.<ref name="Barrett21" /><ref name="Sabertooth2">Template:Cite book</ref> The largest nimravids, Quercylurus and Barbourofelis fricki, were able to reach even larger sizes, weighing Template:Cvt and Template:Convert respectively.<ref name="Peigne3">Template:Cite journal</ref><ref name="Barrett21" /> Dinaelurus had the short face, rounded skull, and smaller canines of the modern cheetah,<ref name="Barrett21" /> and some such as E. bidentatus and Nanosmilus, were only the size of a small bobcat.<ref>Martin, L. D. (1991, January). A new miniature saber-toothed nimravid from the Oligocene of Nebraska. In Annales 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.</ref><ref>Template:Cite book</ref>
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Phylogeny
The phylogenetic relationships of Nimravidae are shown in the following cladogram:<ref name="Alexander Averianov 2016" /><ref name="Barrett16" /><ref>Template:Cite journal</ref>
A 2021 study divides Nimravidae into Hoplophoninae and Nimravinae, the latter including the bulk of species in addition to barbourofelins.
Phylogeny of Nimravidae from the 2022 description of Pangurban:<ref name="Pangurban" />
Evolution
The ancestors of nimravids and cats diverged from a common ancestor soon after the Caniformia–Feliformia split, in the middle Eocene about 50 million years ago (Mya), with a minimum constraint of 43 Mya.
Some of the first nimravids, Maofelis and Pangurban, appeared in the middle of the Eocene epoch, about 40 Mya, in Asia and North America respectively.<ref name="Alexander Averianov 20162">Template:Cite journal</ref> 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 the Oligocene, and nimravids evidently flourished in this environment. North America and Asia were connected and shared much related fauna.<ref name="Prothero">Template:Cite book</ref> Europe in the Oligocene was more of an archipelago than a continent, though some land bridges must have existed, for nimravids also spread there. Barbourofelins probably evolved from Nimravinae dispersing into Africa during the Oligocene. The presence of large hyaenodonts 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.<ref name="Barrett21" />
Extinction
Both Hoplophoninae and Nimravinae died out during the Oligocene epoch, with the last taxa going extinct 29.5 and 25.9 million years ago respectively. Their extinction probably coincided with the expansion of grasslands and possibly competition with amphicyonids.<ref name="Castellanos-2025a">Template:Cite journal</ref><ref name="Antón-2013" /> Their extinction started the infamous cat gap, a 7 million year period when no cat-like predators present in North America.<ref name="Antón-2013">Template:Cite book</ref>
Barbourofelins went extinct around 7 million years ago, during the Late Miocene, for unknown reasons.<ref name="Barrett21" /> Antón Mauricio suggested competition with machairodonts such as Machairodus and Nimravides, may have contributed to their extinction, as barbourofelins were widely successful despite the wider expansion of grasslands.<ref name="Antón-2013" /> However, Paul Barret has contested this hypothesis because of the limited temporal overlap between both clades.<ref name="Barrett21" /> In addition, Albanosmilus, the last genus to go extinct in Eurasia, was also able to coexist and compete with machairodonts Amphimachairodus and Machairodus in some localities for over a million years.<ref name="Jiangzuo-2023">Template:Cite journal</ref><ref name=Morlo2006>Template:Cite journal</ref><ref name="Domingo-2017">Template:Cite journal</ref> Other experts suggested it was more likely they went extinct because of the faunal overturn during the Late Miocene due to the wider expansion of grasslands.<ref name="Barrett21" /><ref name="Jiangzuo2022">Template:Cite journal</ref><ref name=Morlo2006>Template:Cite journal</ref>
Morphology
Most nimravids had muscular, low-slung, cat-like bodies, with shorter legs and tails than are typical of cats. Unlike extant Feliformia, the nimravids had a different bone structure in the small bones of the ear. The middle ear of true cats is housed in an external structure called an auditory bulla, which is separated by a septum into two chambers. Nimravid remains show ossified bullae with no septum, or no trace at all of the entire bulla. They are assumed to have had a cartilaginous housing of the ear mechanism.<ref name="Turner">Template:Cite book</ref> Nimravid feet were short, indicating they walked in a plantigrade or semiplantigrade posture, i.e., on the flat of the feet rather than the toes, like modern cats.<ref name="Antón-2013" />
Although some nimravids physically resembled the saber-toothed cats, such as Smilodon, they were not closely related,<ref>Template:Cite news</ref> but evolved a similar form through parallel evolution. They had synapomorphies with the barbourofelins in the cranium, mandible, dentition, and postcranium.<ref>Template:Cite journal</ref> They also had a downward-projecting flange on the front of the mandible as long as the canine teeth, a feature that also convergently evolved in the saber-toothed sparassodont Thylacosmilus. While most nimravids were thought to have been ambush predators,<ref name="Naples-2008">Template:Cite journal</ref><ref name="Ormsby-2021">Template:Cite thesis</ref><ref name="Morlo-2010">Template:Cite book</ref><ref name="Castellanos-2025c">Template:Cite journal</ref> some such as Eusmilus adelos and Pogonodon davisi were recovered as pounce-pursuit predators.<ref name="Castellanos-2025b">Template:Cite journal</ref> Albanosmilus whitfordi and Dinaelurus are thought to have been cursorial predators, although no post cranial remains have been found for Dinaelurus.<ref name="HB">Template:Cite book</ref><ref>Template:Cite journal</ref><ref name="Barrett21" />
A 2021 study has shown that a sizeable number of species developed feline-like morphologies in addition to saber-toothed taxa.<ref name="Barrettetal21" />
References
External links
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