Nimravides

''Nimravides'' is a genus of extinct saber-toothed cats that was endemic in North America during the Late Miocene, from 11 to 6.5 Ma. Despite its scientific name, ''Nimravides'' does not belong to the Nimravidae, but is a true cat belonging to the family Felidae.

Taxonomy

The genus ''Nimravides'' was originally described by Kitt in 1958 for the species ''"Pseudaelurus" thinobates''. In 1969, Dalquest described the species ''Pseudaelurus hibbardi''. The species ''Machaerodus catocopis'' was described by Cope in 1887, based on a partial mandible from the Loup Fork Beds. The species ''Pseudaelurus thinobates'' and ''Pseudaelurus pedionomus'' were both described by James Reid MacDonald in 1948.

In 1975, Martin and Schultz reassigned ''Machairodus catacopsis'' to ''Nimravides'' and suggested that ''N. thinobates'' was a junior synonym of the former species. The species ''N. galiani'' was first described in 1981 based on fragmentary material from the Love Bone Beds in Florida. The same paper also described additional fossils of ''N. thinobates'' compared to the holotype of ''N. catacopsis'', and concluded that ''N. catacopsis'' was best considered a ''nomen vanum'' and the material assigned to it should be considered ''N. thinobates''.

''"Pseudaelurus" pedionomus'' was reassigned to ''Nimravides'' in 1990 by Beaumont. In 2003, Tom Rothwell reassigned ''Pseudaelurus hibbardi'' to ''Nimravides''. And in 2010 it was suggested that ''N. hibbardi'' was a junior synonym of '' Adelphailurus kansensis''. In 2013, Mauricio Anton ''et al.'' suggested that ''N. catacopsis'' should be re-reassigned back to '' Machairodus''. But this was refuted in 2022 by Jiangzuo ''et al.'' and in addition, reclassified ''M. lahayishupup'' to ''N. catocopis lahayishupup'', considering it as a local subspecies due to its dental difference being a intraspecific variation based on the large sample.

Description

''Nimravides galiani'' is estimated to weigh on average, according to Meachen 2012. Jiangzuo ''et al.'' 2022 suggested it didn’t overlap with ''N. catocopis'' in size. Compared to ''N. catocopis'' and '' Machairodus aphantistus'', it had a much smaller sexual dimorphism due to the smaller infraspecific variation in size. Many of its postcranial features resembles that of jaguars.

''N. thinobates,'' in a 2012 study, was estimated to weigh on average. However, Jiangzuo ''et al.'' 2022 suggested it was actually similar in size to ''M. aphantistus'', which averaged around .

''N. catocopis'' was the largest species, with adults measuring at the shoulder and was similar in size to a large tiger. It was also possessed of long, powerful legs and a long back. Based on mandibular and dental sizes, this species was slightly larger than ''M. aphantistus'' on average. Hh2 populations of ''N. catocopis'' grew larger than Hh1 populations, this is supported by two large males, from the Ogallala group, having femurs that rivaled the femur length of the American lion. The subspecies ''N. c. lahayishupup'' was also quite large. Based on 7 specimens, it is estimated that the subspecies averaged , based on the size range of . A humerus bone measuring attributed to the subspecies suggest that this cat was far larger than a modern lion, which has a humerus, and is considered to be the largest specimen. This specimen is estimated to have weighed , making this species among the largest felids to ever live.

Paleobiology

Predatory behavior

Forelimb morphology suggests ''N. galiani'' was similar to that of extant felids, due to that it likely practiced strangulation method, relied heavily on its dew claw, and likely practiced pounce-pursuit. The authors suggest due to competition with other open plain carnivorans, it could’ve seek shelters among trees along forest boundaries or hide prey when under stress.

''N. catocopis'' may have preferred prey weighing with maximum prey size being , although it may not have been a large prey specialist. It is estimated that ''N. catocopis'' has a jaw gape of 67.91 degrees, with an effective gape of 38 degrees. Considering that, the effective gape is most vital when it comes to prey capture, the authors argued considering the fact that most predators had a jaw gape between 45 and 65 degrees, likely suggests not all saber tooth predators were large prey specialist.'' ^{Including supplementary materials}''

Paleoecology

''N. galiani'' was found in the Love Bone Beds deposits (of Clarendonian Age), which had a mixture of grassland, riverine forest, and marshes, in which it would have shared territory with herbivorous animals like the amphibious rhinoceros '' Teleoceras'', the protoceratid '' Synthetoceras'', the camel '' Aepycamelus'', horses like '' Neohipparion'' and '' Nannippus'', and coexisting with barbourfelini ''Barbourofelis'' ''loveorum'', along with borophaginae canids such as '' Epicyon'' and '' Borophagus'', and the agriotheriini bear '' Agriotherium''. ''B. loveorum'' and ''N. galiani'' likely niche partitioned and competition would’ve been minimal due to different prey and habitat preferences. The robust forelimbs of ''Barbourofelis'' suggests it preferred forested environments, while ''Nimravides'' preferred more open habitats, such as open grasslands. The larger sizes of the ''Nimravides’'' metacarpals, suggests it would’ve preyed upon larger animals compared to ''Barbourofelis.''

''N. catocopis'' was found in Hemphillian rocks such as Chalk Hills Formation, Rattlesnake Formation, McKay Formation, and Ogallala Formation. Rattlesnake Formation was a floodplain environment where the Rattlesnake Ash Fall Tuff is present. It coexisted with herbivores such as the aceratheriinae rhino '' Teleoceras fossiger'', “shovel tusker” amebelodontidae '' Amebelodon'', extinct horse '' Pliohippus spectans,'' and extinct lamini '' Hemiauchenia vera''. Other carnivorans present in the formation was the agriotheriini bear ''Indarctos'' ''oregonensis'' and extinct fox '' Vulpes stenognathus.'' Some of these herbivores, such as ''Teleoceras'' and ''Hemiauchenia'', may have been preyed upon by ''Nimravides''.

Due to its rarity and different habitat preferences, '' Amphimachairodus'' likely didn’t outcompete ''Nimravides''; instead, faunal turnover during the Hemphillian stage was the likely cause of their extinction.

References

{{Taxonbar, from1=Q646185, from2=Q122073749, from3=Q111041041, from4=Q111041029, from5=Q111041069, from6=Q111041238

Homotherini
Miocene carnivorans
Prehistoric carnivoran genera
Miocene mammals of North America