Nimravidae

Nimravidae is an extinct family of carnivorans, sometimes known as false saber-toothed cats, whose fossils are found in North America 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 Tortonian stages, 40.4—7.2 million years ago), spanning about 33.2 million years.[1]

Nimravidae Temporal range: Middle Eocene to Late Miocene, 40–7.246 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Hoplophoneus mentalis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Suborder:	Feliformia
Family:	†Nimravidae Cope, 1880
Genera
†Dinailurictis †Dinictis †Eofelis †Maofelis †Pogonodon †Quercylurus Tribe †Nimravini †Dinaelurus †Nimravus Tribe †Hoplophoneini †Eusmilus †Hoplophoneus †Nanosmilus

The barbourofelids were formerly classified as a subfamily of the Nimravidae but were reassigned to their own distinct family Barbourofelidae in 2004.[2]

Morphology and evolution

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.[3] Nimravid feet were short, indicating they walked in a plantigrade or semiplantigrade posture.[4]

Although some nimravids physically resembled the sabre-toothed cats of the genus Smilodon, they were not closely related,[5] but evolved a similar form through parallel evolution. They possessed synapomorphies with the barbourofelids in the cranium, mandible, dentition, and postcranium.[6] They also had a downward-projecting flange on the front of the mandible as long as the canine teeth, a feature which also convergently evolved in the sabre-toothed sparassodont Thylacosmilus.

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. Recognizable nimravid fossils date from the late Eocene (37 Mya), from the Chadronian White River Formation at Flagstaff Rim, Wyoming, to the late Miocene (5 Mya). Nimravid diversity appears to have peaked about 28 Mya.

Taxonomy

The family Nimravidae was named by American paleontologist Edward Drinker Cope in 1880,[7] 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).[8]

Nimravids are placed in tribes by some authors to reflect closer relationships in 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 sabre-tooths".

Not only did nimravids exhibit diverse dentition, but they also showed the same diversity in size and morphology as cats. Some were leopard-sized, others the size of today's lions and tigers, one had the short face, rounded skull, and smaller canines of the modern cheetah, and one, Nanosmilus, was only the size of a small bobcat.

Classification

The Barbourofelids are no longer included in Nimravidae, following elevation to family as sister clade to the true cats (family Felidae).[9][10]

Family †Nimravidae

Tribe	Image	Genus	Species
		†Dinailurictis (Helbing, 1922)	†D. bonali
		†Dinictis (Leidy, 1854)	†D. felina
		†Eofelis (Kretzoi, 1938)	†E. edwardsii †E. giganteus
		†Maofelis[11] (Averianov et al., 2016)	†M. cantonensis
		†Pogonodon (Cope, 1880)	†P. davisi †P. platycopis
		†Quercylurus (Ginsburg 1979)	†Q. major
†Nimravini		†Dinaelurus (Eaton, 1922)	†D. crassus
		†Nimravus (Cope, 1879)	†N. brachyops †N. intermedius
†Hoplophoneini		†Hoplophoneus[12] (Cope, 1874)  (Subgenus: †Eusmilus[12] (Eaton, 1922))	†H. bidentatus   †H. cerebralis  †H. dakotensis †H. mentalis †H. occidentalis †H. oharrai †H. primaevus  †H. sicarius  †H. villebramarensis
		†Nanosmilus (Martin, 1992)	†N. kurteni

Phylogeny

The phylogenetic relationships of Nimravidae are shown in the following cladogram:[13][11][12]

†Nimravidae

†Maofelis  †Maofelis cantonensis     MA-PHQ 348      †Nimravini   †Nimravus    †Nimravus brachyops     †Nimravus intermedius      †Dinaelurus  †Dinaelurus crassus        †Eofelis    †Eofelis edwardsii     †Eofelis giganteus        †Dinailurictis  †Dinailurictis bonali    †Quercylurus  †Quercylurus major      †Pogonodon    †Pogonodon davisi     †Pogonodon platycopis      †Dinictis  †Dinictis felina    †Hoplophoneini   †Nanosmilus  †Nanosmilus kurteni    †Hoplophoneus    †Hoplophoneus primaevus     †Hoplophoneus oharrai       †Hoplophoneus occidentalis       †Hoplophoneus mentalis       †Hoplophoneus dakotensis    (†"Eusmilus")    †Hoplophoneus bidentatus       †Hoplophoneus cerebralis       †Hoplophoneus villebramarensis     †Hoplophoneus sicarius

Natural history

Restoration of Dinictis and Protoceras by Charles R. Knight

Nimravids appeared in the middle of the Eocene epoch, about 40 mya, in North America and Asia. 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.[14] Europe in the Oligocene was more of an archipelago than a continent, though some land bridges must have existed, for nimravids also spread there.

In the Miocene, the fossil record suggests that many animals suited for living in forest or woodland were replaced by grazers suited for grassland. This suggests that much of North America and Asia became dominated by savanna. Nimravids disappeared along with the woodlands, but survived in relictual humid forests in Europe to the late Miocene. When conditions ultimately changed there in the late Miocene, the last nimravids disappeared about 9 mya.[14]

References

1. Nimravidae in the Paleobiology Database
2. Morlo, Michael; Peigné, Stéphane; Nagel, Doris (January 2004). "A new species of Prosansanosmilus: implications for the systematic relationships of the family Barbourofelidae new rank (Carnivora, Mammalia)". Zoological Journal of the Linnean Society. 140 (1): 43. doi:10.1111/j.1096-3642.2004.00087.x.
3. Turner, Alan (1997). The Big Cats and their Fossil Relatives: an illustrated guide. New York: Columbia University Press. p. 234. ISBN 0-231-10228-3.
4. Antón, Mauricio (2013). Sabertooth. Bloomington, Indiana: University of Indiana Press. p. 90. ISBN 9780253010421.
5. "Meet the Cat Family". Junior Observer. The Sunday Observer. Colombo, Sri Lanka: Associated Newspapers of Ceylon. July 16, 2012. Retrieved January 2, 2013.
6. Bryant, Harold N. (Feb 1991). "Phylogenetic Relationships and Systematics of the Nimravidae (Carnivora)". Journal of Mammalogy. Lawrence, Kansas: American Society of Mammalogists. 72 (1): 56–78. doi:10.2307/1381980. JSTOR 1381980.
7. Cope, E. D. (1889). "Synopsis of the Families of Vertebrata". The American Naturalist. 23: 1–29.
8. 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.
9. Michale Morlo; Stéphane Peigné & Doris Nagel (January 2004). "A new species of Prosansanosmilus: implications for the systematic relationships of the family Barbourofelidae new rank (Carnivora, Mammalia)". Zoological Journal of the Linnean Society. 140 (1): 43. doi:10.1111/j.1096-3642.2004.00087.x.
10. 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. ISBN 978-0-19-923445-5.
11. Averianov, Alexander; Obraztsova, Ekaterina; Danilov, Igor; Skutschas, Pavel; Jin, Jianhua (2016-05-10). "First nimravid skull from Asia". Scientific Reports. 6 (1): 25812. Bibcode:2016NatSR...625812A. doi:10.1038/srep25812. ISSN 2045-2322. PMC 4861911. PMID 27161785.
12. Barrett, P.Z. (2016). "Taxonomic and systematic revisions to the North American Nimravidae (Mammalia, Carnivora)". PeerJ. 4: e1658. doi:10.7717/peerj.1658. PMC 4756750. PMID 26893959.
13. 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. ISSN 0300-3256.
14. Prothero, Donald R. (2006). After the Dinosaurs: The Age of Mammals. Bloomington, Indiana: Indiana University Press. pp. 9, 132–134, 160, 167, 174, 176, 198, 222–233. ISBN 978-0-253-34733-6.

• Zoological Journal of the Linnean Society, 2003, 138, 477–493