Miracinonyx (colloquially known as the "American cheetah" or the "New World cheetah") is an extinct genus of felids belonging to the subfamilyFelinae that wasendemic toNorth America from thePleistocene epoch (about 2.5 million to 16,000 years ago) andmorphologically similar to the moderncheetah (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.[1][2] The genus was originally known from fragments of skeletons, but nearly complete skeletons have been recovered fromNatural Trap Cave in northernWyoming.[3]
The two species commonly identified areM. inexpectatus andM. trumani. Sometimes, a third species,M. studeri, is included, but it is more often listed as ajunior synonym ofM. inexpectatus.M. inexpectatus ranged from theBlancan toIrvingtonian ages of North America whileM. trumani was exclusive to theRancholabrean age.[1][4]
The first fossils attributed toMiracinonyx were several isolated teeth fromPort Kennedy Bone Cave fromPennsylvania, dating back to theIrvingtonian age. The American paleontologistEdward Drinker Cope originally considered these to be related to thespotted hyena, and described the material asCrocuta inexpectata in 1895.[5] However, in 1899 he reclassified the specimens asUncia inexpectata, considering them closely related to thesnow leopard.[6]
More fossil material was recovered from deposits of similar age inMaryland andArkansas, where in 1941 American paleontologistGeorge Gaylord Simpson found them all belonging to the same animal, one he considered to be more closely related to thecougar (Puma concolor), naming the animal asFelis (Puma) inexpectata.[7]
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.[8] However, a 1976 review of fossil pumas from Kurtén consideredF. inexpectata andF. studeri to be the same species, withF. inexpectata having priority. The other valid species (then asFelis trumani) was described in 1969 by Orr based on a complete skull from theLate Pleistocene found inCrypt Cave,Nevada.[1]
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.[9] This suggested that the ancestors of the cheetah diverged from thePuma lineage in the Americas and migrated back to the Old World, a claim repeated as recently asJohnson et al. (2006),[10] and byDobrynin et al. (2015)[11] However, other research by Barnett and Faurby, through examiningmitochondrial DNA and reanalyzing morphology, has suggested reversing the reclassification: the American cheetah developed cheetah-like characteristics throughparallel evolution, but it is most closely related toPuma and not to the modern cheetah ofAfrica andAsia.[1][12][13] Moreover, Faurby notes that noAcinonyx fossils have been found in North America, and noMiracinonyx fossils elsewhere. However,O'Brien et al. (2016) posit that the supposedhomoplasy between the genera is controversial, as it is asserted that is not necessarily any conclusive anatomical or genetic basis for dismissing ahomologous relationship betweenAcinonyx andMiracinonyx.[14] 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 theOld World or theNew World.[15]
The cougar andM. trumani are believed to have split from a cougar-like ancestor around three million years ago;[12] whereM. inexpectatus fits in is unclear, although it is probably a more primitive version ofM. trumani.[16]
Below is the phylogeny fromChimento & Dondas (2017) when describing the earliest known fossil record of cougars inSouth America. As shown here, they foundMiracinonyx to be a sister taxon toPuma (though in their paper they considered the former genus to be an extinct subgenus of the latter).[17]
Adams (1979) found these animals to be intermediates in size and morphology between cheetahs and cougars and decided to place them in their own genusMiracinonyx.[9]
The name is a combination of theLatinmīrus ("wonderful") andAcinonyx, the cheetah family, itself a combination of theGreekἀκίνητος (akī́nētos) meaning "unmoved" or "motionless" andὄνυξ (ónyx) meaning "nail" or "hoof".[9]
It has been proposed thatMiracinonyx is an instance ofparallel evolution with the cheetah of theAcinonyx 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.[1][18] 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 inAcinonyx during high-speed chases, though this may reflect the colder temperatures of Pleistocene North America compared to Africa and Iran.[19] Additionally, the injuries that led to the death of a sub-adultMiracinonyx according to a 2022 research article by John-Paul Michael Hodnettet al suggest thatMiracinonyx felids, like extant cats such as the puma, regularly fought one another; instances of conspecific aggression amongAcinonyx cheetahs are relatively rare.[2][4][20]Miracinonyx species were also larger than a modern cheetah and similar in size to a modernNorth American cougar. The body mass was typically around 70 kg (150 lb), with a head-and-body length of 170 cm (67 in), tail length around 92 cm (36 in), and shoulder height of 85 cm (33 in).[21] Large specimens could have weighed more than 95 kg (209 lb).[22]Miracinonyx most likely preyed onmountain goats (Oreamnus americanus),horses (Equus sp.) and especiallypronghorns (Antilocapra americana).
It is often assumed that pronghorns evolved to evadeMiracinonyx, 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.[23] 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 andperissodactyls 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.[24][25][26]
Fossils from Arizona show that American cheetahs were territorial animals, with evidence of pathologies being found on some of the bones.[27][28][29][4]
M. inexpectatus, ranging from theBlancan toIrvingtonian ages, and was more similar to the cougar in build thanM. trumani.[4][15] Fossil remains ofM. inexpectatus found inHamilton Cave inWest Virginia show that this creature lived with and competed with other large cats likejaguars (Panthera onca) and the saber-toothed cat (Smilodon sp.).[1][30]
M. trumani, exclusive to theRancholabrean age, was more cursorial andCheetah-like thanM. inexpectatus,[4][15] but unlike cheetahs, both species retained fully retractable claws.[1][2] This genus likely hunted in a way with no modern analogues as its elbow-joint morphology was intermediate betweenA. jubatus andP. concolor.[2]
Fossils ofM. inexpectatus have also been found in Florida,[51][52][53][54][55]Texas,[56] Colorado,[57]Georgia,[42] South Carolina,[42][58] Pennsylvania,West Virginia,[59] Maryland,[60] andCalifornia.[61][62] 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.[63] In 2022, the skeletal remains of aM. inexpectatus were retrieved from a cave in southwesternVirginia.[64]
^Cope, Edward D. (1895). "The fossil vertebrata from the fissure at Port Kennedy, Pa".Proceedings of the Academy of Natural Sciences of Philadelphia.47:446–450.JSTOR4061990.
^Cope, Edward D. (1899). "Vertebrate remains from Port Kennedy bone deposit".Journal of the Academy of Natural Sciences of Philadelphia.11 (2).
^Savage, Donald E. (1960). "A Survey of Various Late Cenozoic Vertebrate Faunas of the Panhandle of Texas: Felidae". University of California Press.{{cite journal}}:Cite journal requires|journal= (help)
^Haaramo, Mikko (2005-11-15)."Felinae – small cats". Felidae.Mikko's phylogeny archive. Archived fromthe original on 2007-03-27. Retrieved2007-02-20.
^Chimento, N.R.; Dondas, A. (2017). "First record ofPuma concolor (Mammalia, Felidae) in the Early-Middle Pleistocene of South America".Journal of Mammalian Evolution.25 (3):381–389.doi:10.1007/s10914-017-9385-x.hdl:11336/48212.S2CID16249074.
^Van Valkenburg, Blaire; Pang, Benison; Cherin, Marco; Rook, Lorenzo (2018)."The Cheetah: The Evolutionary History and Paleoecology". In Marker, Laurie; K. Boast, Lorraine; Schmidt-Kuntzel, Anne (eds.).Cheetahs: Biology and Conservation: Biodiversity of the World: Conservation from Genes to Landscapes. Academic Press. pp. 25–32.ISBN978-0-12-804120-8.
^Caro, T.M. (1994).Cheetahs of the Serengeti Plains: Group Living in an Asocial Species. Chicago: University of Chicago Press. p. 500.ISBN978-0-226-09433-5.
^The microtine rodents of the Cheetah Room fauna, Hamilton Cave, West Virginia, and the spontaneous origin of Synaptomys (Report). 1988.doi:10.3133/b1853.
^Carranza-Castañeda, Oscar; Miller, Wade E. (May 1996). "Hemphillian and Blancan Felids from central Mexico".Journal of Paleontology.70 (3):509–518.doi:10.1017/s0022336000038439.ISSN0022-3360.
^editor., Baskin, Jon A., editor. Czaplewski, Nicholas J., editor. Lucas, Spencer G., editor. McDonald, H. Gregory (Hugh Gregory), 1951- editor. Mead, Jim I., editor. White, Richard S. Jr., editor. Lichtig, Asher J. (2022).Late Cenozoic vertebrates from the American Southwest: a tribute to Arthur H. Harris. New Mexico Museum of Natural History and Science.OCLC1350541559.{{cite book}}:|last= has generic name (help)CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
^abcSanders, A.E. (2002). "Additions to the Pleistocene Mammal Faunas of South Carolina, North Carolina, and Georgia".Transactions of the American Philosophical Society.92 (5): i.doi:10.2307/4144916.JSTOR4144916.
^Scott, M.; Gary, S. (1987).Late Pliocene (Late Blancan) vertebrates from the St. Petersburg Times site, Pinellas County, Florida, with a brief review of Florida Blancan faunas. Florida Paleontological Society.OCLC182860777.
^Simpson, G.G. (1929).Pleistocene mammalian fauna of the Seminole Field, Pinellas County, Florida. American Museum of Natural History.OCLC729432.
^Morgan, Gary S.; Seymour, Kevin L. (1997-10-01). "Fossil history of the panther (Puma concolor) and the cheetah-like cat (Miracinonyx inexpectatus) in Florida".Bulletin of the Florida Museum of Natural History.40 (2):177–219.doi:10.58782/flmnh.emto6774.ISSN0071-6154.
^Kohn, M.J.; McKay, M.P.; Knight, J.L. (2005). "Dining in the Pleistocene—Who's on the menu?".Geology.33 (8):649–652.doi:10.1130/g21476ar.1.S2CID55786870.
^Van Valkenburgh, Blaire; Grady, Frederick; Kurtén, Björn (1990-12-20). "The Plio-Pleistocene cheetah-like catMiracinonyx inexpectatusof North America".Journal of Vertebrate Paleontology.10 (4):434–454.doi:10.1080/02724634.1990.10011827.ISSN0272-4634.
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