Miracinonyx, also called the American cheetah or New World cheetah, is an extinct group of cats in the Felinae subfamily. It lived only in North America during the Pleistocene epoch (about 2.5 million to 16,000 years ago). Miracinonyx looked similar to modern cheetahs (Acinonyx jubatus), but scientists question whether it filled the same ecological role because its body structure likely limited its ability to chase prey quickly. Scientists first found Miracinonyx from pieces of bones, but nearly complete skeletons were later discovered in Natural Trap Cave in northern Wyoming.

Miracinonyx was first classified as a subgroup of the Acinonyx genus, with M. trumani as the type species. M. studeri was once considered a second species, but it is now often listed as a junior synonym of M. inexpectatus. M. trumani lived only during the Rancholabrean age, while M. inexpectatus existed from the late Blancan to Irvingtonian ages in North America.

Discovery and naming

The first fossils connected to Miracinonyx were several separate teeth found in Port Kennedy Bone Cave in Pennsylvania, from the Irvingtonian age. Edward Drinker Cope, an American paleontologist, first thought these fossils were related to the spotted hyena and named them Crocuta inexpectata in 1895. Later, in his 1899 publication, he changed his classification and called them Uncia inexpectata, believing they were closely related to the snow leopard.

More fossils from the same time period were found in Maryland and Arkansas. In 1941, George Gaylord Simpson, another American paleontologist, studied these fossils and determined they belonged to a single animal. He believed this animal was more closely related to the cougar (Puma concolor) and named it Felis (Puma) inexpectata.

The type species, originally called Felis trumani, was described in 1969 by Phil C. Orr based on a complete skull from the Late Pleistocene found in Crypt Cave, Nevada. In 1979, Daniel B. Adams created a new subgenus called Miracinonyx within the genus Acinonyx and assigned F. trumani as the type species: Acinonyx (Miracinonyx) trumani. The name Miracinonyx comes from the Latin word mirus ("surprising") and the genus Acinonyx, which includes the modern cheetah.

Another species, originally named Felis studeri, was described in 1960 by Donald E. Savage based on more complete remains, including many bones and skull parts. In 1976, Björn Kurtén reviewed fossil pumas and suggested that F. inexpectata and F. studeri were the same species, with F. inexpectata having priority. In 1979, Adams included F. studeri as a second species of Miracinonyx, naming it Acinonyx (Miracinonyx) studeri. While he agreed with Kurtén’s idea that F. inexpectata and F. studeri were the same, he considered F. inexpectata uncertain due to the holotype being a broken 4th premolar. In 1990, Blaire Van Valkenburgh and colleagues placed Miracinonyx into its own genus and confirmed that F. studeri and F. inexpectata were the same, creating the new combination M. inexpectatus.

Taxonomy and evolution

Research about the American cheetah has led to different conclusions. Scientists first thought it was related to cougars, but studies in the 1970s changed this, showing it was more closely related to cheetahs. This suggested that cheetah ancestors split from the cougar family in the Americas and later moved to the Old World. This idea was supported by studies from Johnson et al. (2006) and Dobrynin et al. (2015). However, other research by Barnett and Faurby, using mitochondrial DNA and reanalyzing physical traits, argued that the American cheetah developed cheetah-like features separately, making it more closely related to cougars than to modern cheetahs in Africa and Asia. Faurby also noted that no fossils of Acinonyx (modern cheetahs) have been found in North America, and no Miracinonyx (American cheetah) fossils have been found elsewhere. O'Brien et al. (2016) questioned whether the similarities between the two groups are due to shared ancestry or independent evolution, as there is no clear evidence to support either view. The origin of modern cheetahs remains debated, but Miracinonyx is believed to have evolved from ancestors similar to cougars, regardless of where this happened.

Scientists think the cougar and M. trumani split from a common ancestor about three million years ago. The role of M. inexpectatus in this timeline is unclear, but it may be an earlier version of M. trumani.

A phylogeny from Chimento & Dondas (2017) describes the earliest known cougar fossils in South America. Their study showed that Miracinonyx is closely related to Puma, though they considered Miracinonyx an extinct subgroup of Puma.

Description

Some scientists think Miracinonyx evolved similarly to cheetahs, but recent studies show it was not as specialized for chasing prey. Unlike cheetahs, Miracinonyx had retractable claws and could turn its front legs inward to grab prey, which may have made it slower. It was more closely related to cougars. M. trumani may have hunted in a way that is not seen in modern animals, possibly relying less on speed than cheetahs. Its brain was similar to a cougar’s, but had features in the parts that process sound and sight like those of cheetahs. This may have made it less ready for the hunting style of true cheetahs. Miracinonyx also had less developed paranasal sinuses, which help cheetahs avoid brain overheating during fast runs. This may have been because the colder climate of Pleistocene North America compared to Africa and Iran affected these features. A 2022 study by Hodnett and others found that Miracinonyx, like modern cougars, sometimes fought each other. This behavior is rare in cheetahs. Miracinonyx was larger than modern cheetahs and about the same size as cougars. It weighed around 70 kg (150 lb), had a body length of 170 cm (67 in), a tail length of 92 cm (36 in), and stood about 85 cm (33 in) tall at the shoulders. Some individuals may have weighed over 95 kg (209 lb). Miracinonyx likely hunted mountain goats, horses, and especially pronghorns.

It is often thought that pronghorns evolved to escape Miracinonyx, but this idea is still debated. Recent research suggests pronghorns’ speed may have developed due to many factors, including pressure from prehistoric wolves, lions, and changes in grassland environments. During the Miocene epoch, grasslands with C4 plants replaced forests in North America, changing the landscape. This led to animals like horses and deer evolving longer legs and teeth suited for eating grasses. True fast predators, like cheetahs, did not appear until the Plio-Pleistocene, much later than these changes. However, studies using isotopes show pronghorns were a main food source for Miracinonyx, making up about 40% of their diet. A 2026 study by Hardy and Kort found that pronghorns developed speed adaptations before Miracinonyx appeared.

Behavior

Miracinonyx probably hunted fast-running animals like Antilocapra, the extinct Tetrameryx, and Stockoceros. Other prey included horses (Equus sp.), bighorn sheep, and mountain goats. Fossils found in Arizona show that M. trumani was a territorial animal, with signs of injuries or diseases on some bones.

M. inexpectatus had a body shape more similar to a cougar than M. trumani. Fossils of M. inexpectatus discovered in Hamilton Cave in West Virginia indicate that this animal lived alongside and competed with other large cats, such as jaguars (Panthera onca) and the saber-toothed cat (Smilodon sp.). M. trumani was more fast-running and resembled a cheetah more than M. inexpectatus. However, unlike cheetahs, both species had fully retractable claws. This genus likely hunted in a way that has no modern equivalent, as its elbow joint shape was between that of A. jubatus and P. concolor.

Fossil distribution

Fossil remains of Miracinonyx have been found across the United States and as far south as Mexico. Fossils have also been discovered 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 fossils of M. trumani were found in the Natural Trap Cave in northern Wyoming. Fossils discovered in Arizona have helped scientists learn more about this mysterious cat.

Fossils of M. inexpectatus have also been found in Florida, Texas, Colorado, Georgia, South Carolina, Pennsylvania, West Virginia, Maryland, and California. Some fossils from California, including those from Rancho La Brea and the McKittrick Tar Seeps, were first thought to belong to Puma concolor but were later identified as Miracinonyx trumani. This change in classification shows that Miracinonyx trumani lived in a wider area and in different environments in late Pleistocene California. In 2022, the bones of a M. inexpectatus were found in a cave in southwestern Virginia.

M. inexpectatus lived during the late Blancan and Irvingtonian ages (Early to Middle Pleistocene), while M. trumani existed only during the Rancholabrean age (late Middle to Late Pleistocene). The youngest known M. trumani specimen was found at the Haystack Cave. Based on the remains of an unidentified mammal in layers 3 and 4 of the site, the most reliable radiocarbon dating suggests the Haystack Cave site is about 19,659–16,604 years old (14,935 ± 610 years uncalibrated). This date is believed to be the most recent known time that M. trumani lived.