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

File:Nimravides galiani FLMNH.jpg

Skull cast of N. galiani, Florida Museum of Natural History

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 Template:Cvt. 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.