American Cheetah

''Miracinonyx'' (colloquially known as the "American cheetah" or the "New World cheetah") is an extinct genus of felids belonging to the subfamily Felinae that was endemic to North America from the Pleistocene epoch (about 2.5 million to 16,000 years ago) and morphologically similar to the modern cheetah (''Acinonyx jubatus''), although its apparent similar ecological niches have been considered questionable due to anatomical morphologies of the former that would have limited its ability to act as a specialized pursuit predator. The genus was originally known from fragments of skeletons, but nearly complete skeletons have been recovered from Natural Trap Cave in northern Wyoming.

The two species commonly identified are ''M. inexpectatus'' and ''M. trumani''. Sometimes, a third species, ''M. studeri'', is included, but it is more often listed as a junior synonym of ''M. inexpectatus''. ''M. inexpectatus'' ranged from the Blancan ages of North America while ''M. trumani'' was exclusive to the Rancholabrean age.

Discovery and naming

The first fossils attributed to ''Miracinonyx'' were several isolated teeth from Port Kennedy Bone Cave from Pennsylvania, dating back to the Irvingtonian age. The American paleontologist Edward Drinker Cope originally considered these to be related to the spotted hyena, and described the material as ''Crocuta inexpectata'' in 1895. However, in 1899 he reclassified the specimens as ''Uncia inexpectata'', considering them closely related to the snow leopard.

More fossil material was recovered from deposits of similar age in Maryland and Arkansas, where in 1941 American paleontologist George Gaylord Simpson found them all belonging to the same animal, one he considered to be more closely related to the cougar (''Puma concolor''), naming the animal as ''Felis (Puma) inexpectata''.

A second species, ''Felis studeri'', was described by D. E. Savage in 1960 based on a more complete material consisting of extensive postcranial and cranial material of the animal. However, a 1976 review of fossil pumas from Kurtén considered ''F. inexpectata'' and ''F. studeri'' to be the same species, with ''F. inexpectata'' having priority. The other valid species (then as ''Felis trumani'') was described in 1969 by Orr based on a complete skull from the Late Pleistocene found in Crypt Cave, Nevada.

Taxonomy and evolution

Research into the American cheetah has been contradictory. It was originally believed to be an early cougar representative, before being reclassified in the 1970s as a close relative of the cheetah. This suggested that the ancestors of the cheetah diverged from the ''Puma'' lineage in the Americas and migrated back to the Old World, a claim repeated as recently as , and by However, other research by Barnett and Faurby, through examining mitochondrial DNA and reanalyzing morphology, has suggested reversing the reclassification: the American cheetah developed cheetah-like characteristics through parallel evolution, but it is most closely related to ''Puma'' and not to the modern cheetah of Africa and Asia. Moreover, Faurby notes that no ''Acinonyx'' fossils have been found in North America, and no ''Miracinonyx'' fossils elsewhere. However, posit that the supposed homoplasy between the genera is controversial, as it is asserted that is not necessarily any conclusive anatomical or genetic basis for dismissing a homologous relationship between ''Acinonyx'' and ''Miracinonyx''. The veracity of the origin of the modern cheetah is also debated; however, ''Miracinonyx'' is believed to have evolved from cougar-like ancestors, regardless of whether in the Old World or the New World.

The cougar and ''M. trumani'' are believed to have split from a cougar-like ancestor around three million years ago; where ''M. inexpectatus'' fits in is unclear, although it is probably a more primitive version of ''M. trumani''.

Below is the phylogeny from when describing the earliest known fossil record of cougars in South America. As shown here, they found ''Miracinonyx'' to be a sister taxon to ''Puma'' (though in their paper they considered the former genus to be an extinct subgenus of the latter).

found these animals to be intermediates in size and morphology between cheetahs and cougars and decided to place them in their own genus ''Miracinonyx''.

The name is a combination of the Latin ("wonderful") and ''Acinonyx'', the cheetah family, itself a combination of the Greek () meaning "unmoved" or "motionless" and () meaning "nail" or "hoof".

Description

It has been proposed that ''Miracinonyx'' is an instance of parallel evolution with the cheetah of the ''Acinonyx'' genus. Recent studies, however, suggest that it was not as specialized in chasing as the cheetah, as it retained retractable claws and could supinate its forelimbs to grapple with prey, which may have diminished its ability to run fast compared to the true cheetah. Instead, it was more closely related to the cougar; ''M. trumani'' might have employed a hunting behavior without modern analogue, which may not have relied on speed as much as a cheetah. ''M. trumani'' also had a brain similar to a cougar's, albeit with cheetah-like adaptations in the auditory and visual cortexes, and therefore was not as cognitively prepared for the predatory behavior of true cheetahs. Moreover, it had underdeveloped paranasal sinuses which prevents the brain from overheating in ''Acinonyx'' during high-speed chases, though this may reflect the colder temperatures of Pleistocene North America compared to Africa and Iran. Additionally, the injuries that led to the death of a sub-adult ''Miracinonyx'' according to a 2022 research article by John-Paul Michael Hodnett ''et al'' suggest that ''Miracinonyx'' felids, like extant cats such as the puma, regularly fought one another; instances of conspecific aggression among ''Acinonyx'' cheetahs are relatively rare. ''Miracinonyx'' species were also larger than a modern cheetah and similar in size to a modern North American cougar. The body mass was typically around , with a head-and-body length of , tail length around , and shoulder height of . Large specimens could have weighed more than . ''Miracinonyx'' most likely preyed on mountain goats (''Oreamnus americanus''), horses (''Equus'' sp.) and especially pronghorns (''Antilocapra americana'').

It is often assumed that pronghorns evolved to evade ''Miracinonyx'', but this is still debated. Recent research has suggested that the pronghorn's speed may have been shaped by multiple ecological pressures beyond a single predator, including prehistoric wolves, North American lions, and environmental factors such as open grasslands. In the Neogene period (or more specifically the Miocene epoch), in North America, grassland environments, especially those of C4 carbon fixations, were replacing forested lands in North America as well as C3 plants, causing extensive changes in vegetational structure. As a result, artiodactyls and perissodactyls generally evolved with hypsodont dentition for eating C4 grasses and distally longer limbs for easier movement within open environments. In comparison, true pursuit predators didn't even exist until the Plio-Pleistocene, a more recent development of carnivorans compared to the ungulates that already were built for speed some 20 million years before. This general analysis, however, does not preclude the pronghorn’s unusually high speed being a specific adaption to predation pressure from cheetahs, as isotopic analysis does indicate pronghorn were their preferred prey, making up an estimated 40% of their diet.

Behavior

Fossils from Arizona show that American cheetahs were territorial animals, with evidence of pathologies being found on some of the bones.

''M. inexpectatus'', ranging from the Blancan ages, and was more similar to the cougar in build than ''M. trumani.'''''' Fossil remains of ''M. inexpectatus'' found in Hamilton Cave in West Virginia show that this creature lived with and competed with other large cats like jaguars (''Panthera onca'') and the saber-toothed cat ('' Smilodon'' sp.'')''.

''M. trumani'', exclusive to the Rancholabrean age, was more cursorial and Cheetah-like then ''M. inexpectatus,'' but unlike cheetahs, both species retained fully retractable claws. This genus likely hunted in a way with no modern analogues as its elbow-joint morphology was intermediate between ''A. jubatus'' and ''P. concolor.''

''Miracinonyx'' hunted cursorial prey like '' Antilocapra'' (such as the modern pronghorn) as well as the extinct '' Tetrameryx'' and '' Stockoceros'', and horses (''Equus'' sp.), as well as bighorn sheep and mountain goats.

Fossil distribution

Fossil remains of ''Miracinonyx'' have been found across the United States and as far south as Mexico. Remains have also been unearthed in western Canada. Fossils of ''M. trumani'' have been found in Arizona, New Mexico, Florida, Wyoming, Colorado, Nebraska, South Carolina, Maryland, and Pennsylvania. The most complete finds of ''M. trumani'' are from the Natural Trap Cave in northern Wyoming. The fossils unearthed in Arizona have offered us a better understanding of this enigmatic felid.

Fossils of ''M. inexpectatus'' have also been found in Florida, Texas, Colorado, Georgia, South Carolina, Pennsylvania, West Virginia, Maryland, and California. Some fossil remains from sites in California, including Rancho La Brea and the McKittrick Tar Seeps, were originally misidentified as Puma concolor, but have since been reclassified as Miracinonyx trumani. This revision suggests a broader geographic and ecological range for the species in late Pleistocene California. In 2022, the skeletal remains of a ''M. inexpectatus'' were retrieved from a cave in southwestern Virginia.

References

External links

{{Portal bar, Paleontology, Prehistoric mammals

Piacenzian first appearances
Pleistocene carnivorans
Pleistocene extinctions
Pliocene carnivorans
Prehistoric felids
Felines
Pleistocene mammals of North America
Fossil taxa described in 1979