Miracinonyx

Miracinonyx, colloquially known as the American cheetah, is an extinct genus of cat that was native to North America during the Pliocene and Pleistocene epochs (about 3.1 million to 16,000 years ago). Its closest living relative is the cougar, while its anatomical similarities to the modern cheetah, including large nostrils and long legs adapted for cursoriality (specialization in running), are possibly a result of convergent evolution, the independent development of analogous physical traits due to similar environmental pressures. Unlike the modern cheetah, Miracinonyx also had fully retractable claws and relatively robust legs.

The first fossils ascribed to Miracinonyx were described by the American paleontologist Edward Drinker Cope in the late 19th century, who thought the remains belonged to an extinct relative of the spotted hyena or snow leopard. In 1979, American researcher Daniel B. Adams named Miracinonyx as a subgenus of Acinonyx, the genus that includes the modern cheetah, with M. trumani as the type species. In 1990, American paleontologist Blaire Van Valkenburgh and colleagues recognized Miracinonyx as a distinct genus, and re-evaluated the fossils described by Cope as belonging to an older species of the same genus, M. inexpectatus. Alternatively, Miracinonyx may represent a subgenus of Puma, the genus that includes the cougar, on the basis of genetic evidence supporting a close relationship.

M. inexpectatus lived between the Late Pliocene and Middle Pleistocene (Blancan and Irvingtonian faunal stages), from 3.1 to 0.6 million years ago, while M. trumani lived during the Late Pleistocene (Rancholabrean faunal stage), between 52,000 and 16,000 years ago. The fossils of Miracinonyx were known from the United States, Mexico and Yukon, Canada. Paleontologists initially considered this taxon to be specialized in chasing down cursorial herbivores like the pronghorn on open grasslands.