National Geographic

Did False Cheetahs Give Pronghorn a Need for Speed?

Pronghorn are among the fastest animals on Earth. Often ranked second to the cheetah for mammalian land speed records, America’s peculiar giraffoid has been said to hit top speeds over 50 miles per hour and maintain their sprints for much longer than quick carnivores. The exact figure has been difficult to pin down, but the swiftness of pronghorn in full sprint leaves no doubt that these herbivores are easily capable of outpacing coyotes and other potential predators. But why should pronghorn be so much faster than North America’s carnivores? The answer, some researchers have speculated, lies in prehistory.

Today’s pronghorn species – Antilocapra americana – is the last survivor of a deeper, disparate, and more diverse family that was almost extinguished by the end-Pleistocene extinction about 10,000 years ago. As a group, their record goes back about 17 million years, although when pronghorn of modern aspect evolved is a trickier question. Some researchers have proposed that Antilocapra originated around three million years ago, with Antilocapra americana itself being a late arrival during the Pleistocene, but the scant and neglected record of fossil pronghorn has given researchers cause to be tentative. All we know for sure is that the only surviving pronghorn species evolved sometime during the past two million years, part of the wonderful, mostly-lost megafauna that roamed North America. False cheetahs were among those charismatic, recently-extinct mammals, and have been implicated as the reason pronghorn are so speedy.

Paleontologists started cataloging the remains of North America’s cheetah-wannabes in the late 19th century. Researchers regularly regarded their bones as similar to those of cougars, but distinct enough to merit new species names. Slowly, as paleontologists accumulated additional remains of these felids from places like Natural Trap Cave in Wyoming, the cheetah-like nature of these cats started to come into focus. Although their skeletons still recalled those of cougars, these were long-limbed cats with shortened skulls and enlarged nasal openings – a constellation of traits that hinted at a fast-running lifestyle.

Experts disagreed about exactly what the cats were. Some considered them to be unusual cousins of cougars. University of California, Berkeley paleontologist Daniel Adams thought differently. “The points of similarity [between the North American cats and the African cheetah] are so extensive and of such a complex nature,” Adams wrote in 1979, “that a hypothesis attributing their origin to other than common genetic descent would require pushing the concept of parallel evolution to an unprecedented extreme.” He grouped the North American fossils together under a subgenus – Miracinonyx, a name coined decades before by E.D. Cope – within the genus of the African cheetah Acinonyx. More than that, Adams argued, cheetahs might have evolved in the New World and then spread to the Old.

Better fossils resolved the debate. In 1990, fossil carnivore expert Blaire Van Valkenburgh and colleagues described a nearly-complete cheetah-like cat found in a West Virginia cave. This specimen, compared to others, showed that the leggy North American cats were two species of a distinct genus that was closer to cougars than cheetahs. (Adams had been misled by functional adaptations of the cat skull and legs which had evolved independently.) The earlier Miracinonyx inexpectatus and the later Miracinonyx trumani were false cheetahs – specialized cats whose genus evolved in North America around three million years ago. A molecular analysis of recovered Miracinonyx DNA published in 2005 by Ross Barnett and colleagues confirmed this relationship. America’s svelte Pleistocene cats were agile cougar cousins, not true cheetahs.

Regardless of their ancestry, though, the sleek form of Miracinonyx has inspired paleontologists to envision the carnivore as a cheetah copycat. The long legs and enlarged nasal openings – for better oxygen intake while running – appear to indicate that Miracinonyx sprinted to chase down prey. Pronghorn expert John Byers took this assumption to propose that pronghorn co-evolved with the false cheetahs and other fast carnivores, making the speed of the herbivores a trace of an evolutionary arms race that ended 10,000 years ago.

Byers’ hypothesis became the de facto explanation for pronghorn speed. Advocates of Pleistocene Rewilding – the controversial notion that Old World species should be introduced to New World parks to kickstart evolutionary interactions that have gone dormant since the loss of American megafauana – have even suggested that African cheetah be brought to North America to reinvigorate the evolutionary competition that gave pronghorn reason to run. (I can only wonder what pronghorn would say to this misguided idea.) The logic is simple – fast predator, faster prey. The problem is that visions of false cheetahs running down pronghorn are based on the appearance of speed rather than hard evidence.

We don’t know very much about the natural history of either Miracinonyx species. Their skeletons are cheetah-ish, but that’s not nearly enough to pin these carnivores as the inspiration for artiodactyl agility. In fact, the ecological context of Miracinonyx bones hints that these cats were not simply speedy specialists who prowled open grasslands.

In their 1990 study, Van Valkenburgh and collaborators noted that later Miracinonyx bones have been found from Nebraska to Pennsylvania and Florida in deposits which accumulated under varying conditions. These cats were apparently just as at home among coastal savannahs as mountain stream valleys. More recently, at the 2010 Society of Vertebrate Paleontology meeting, John-Paul Hodnett and coauthors presented a poster about Miracinonyx that frequented caves in prehistoric Grand Canyon, Arizona. There was a distinct lack of fast-running, open-savannah prey animals during the same time period – the researchers noted that the extinct mountain goat Oreamos harringtoni was the most common possibly prey animal in the area. Rather than speeding over the grasslands, Hodnett and colleagues reported, the Grand Canyon Miracinonyx may have lived like snow leopards, bounding down sheer rock faces in pursuit of mountain goats.

This isn’t to say that Miracinonyx never bolted after equally-swift prey. It’s only to point out that we don’t know much about the cat’s ecology, feeding habits, or hunting strategy. There are a few ways we could find out a bit more, though.

Coprolites attributable to Miracinonyx might contain identifiable bone fragments of the cat’s prey. And while such a find is a longshot, perhaps a trackway made by a Miracinonyx running or launching itself into pursuit could tell us about how these cats actually moved. Both lines of evidence suffer from the complexities of accurately attributing a particular trace fossil to a trace-maker, though. Another route may be to compare the isotopic clues in the teeth of Miracinonyx to those of their potential prey, as was recently done for two sabercats and a bear dog found in Spain. By ascertaining where herbivores were feeding, and how geochemical signatures of prey became locked in carnivore teeth, paleontologists could narrow down the preferred habitats and prey of Miracinonyx. Furthermore, a poster presented by Natalia Kennedy and coauthors at the 2012 SVP meeting outlined a new attempt to compare the spine of the modern cheetah to that of Miracinonyx and other extinct cats to see how skeletal anatomy influenced flexibility and lifestyle.

Miracinonyx might have been the reason for the swiftness of pronghorn. False cheetahs and archaic pronghorn overlapped in time, if not habitat, for as much as three million years. But saying Miracinonyx was certainly a speed demon that gave pronghorn a reason to run is only supported by the barest amount of evidence. If we’re going to understand the evolution and natural history of these animals, we must first untangle their histories and the specific details of their ecology. The Just-So story of how the pronghorn got its speed has yet to be tested by the evidence which resides in the fossil record.

References:

Adams, D. 1979. The Cheetah: Native American. Science. 205:1155-1158

Barnett, R., Barnes, I., Phillips, M., Martin, L., Harington, C., Leonard, J., Cooper, A. 2005. Evolution of the extinct sabretooths and the American cheetah-like cat. Current Biology. 15, 15:  R589-90

Hodnett, J., Mead, J., White, R., Carpenter, M.  2010. Miracinonyx trumani (Carnivora: Felidae) from the Rancholabrean of Grand Canyon, Arizona and its implications for he ecology of the “American cheetah”,  in Program and Abstracts, Journal of Vertebrate Paleontology, 30:sup2, 1A-198A

Kennedy, N., Bhatt, R. 2012. A geometric and kinematic backbone model of the cheetah, Acinonyx jubatus, and its application to understanding the spinal kinematics of Miracinonyx trumani, in Programs and Abstracts, Journal of Vertebrate Paleontology

Martin, L., Gilbert, B., Adams, D. 1977. A cheetah-like cat in the North American Pleistocene. Science. 195: 981-982

Van Valkenburgh, B., Grady, F., Kurten, B. 1990. The Plio-Pleistocene cheetah-like cat Miracinonyx inexpectatus of North America. Journal of Vertebrate Paleontology. 10,4 : 434-454

Walker, D. 2000. Pleistocene and Holocene records of Antilocapra americana: A review of the FAUNMAP data. Plains Anthropologist. 45, 174, 32: 13-28

There are 18 Comments. Add Yours.

  1. 220mya
    January 8, 2013

    Are there any individual localities where Miracinonyx and antilocaprid fossils are found at the same stratigraphic horizon?

  2. Brian Switek
    January 8, 2013

    Both are found in Natural Trap Cave. Older Miracinonyx and antilocaprines might overlap in Florida, as well, but I’m not sure. The Walker ref has a map of Pleistocene Antilocapra americana localities, so that might highlight a few areas to check out.

  3. Michael Habib
    January 8, 2013

    Great article, Brian. Any consideration in the literature of a Miracinonyx diet of small prey? (example: leporids). It seems like every time a cat is discussed in the fossil record, the assumption is it took shots at hooved prey items. Poor artiodactyls.

  4. Cris
    January 8, 2013

    Fantastic article!

    I know of at least one Blancan site in Florida where Miracinonyx and Antilocaprid (Capromeryx) material have been found in association.

  5. Brian Switek
    January 8, 2013

    Great question, Mike. My knowledge of the subject is less than encyclopedic, but I haven’t seen any consideration of Miracinonyx targeting small prey. Ever since the cheetah-like nature of the cat became apparent, it has been viewed as a megafaunal predator that partitioned habitats with jaguars and sabercats.

    But you raise an important point. In the sabercat-bear dog paper I mentioned above, the researchers focused on large-bodied prey for isotopic comparisons. As they noted in the paper, though, one bonebed within the wider site contained the remains of multiple small artiodactyls that were apparently eaten by a large carnivore – possibly a bear dog. Too often, I think, we assume that big mammalian carnivores must have eaten large prey (even when there’s no direct evidence for what exactly they hunted).

    I think there are ways to examine and test the hunting and feeding ecology of Miracinonyx. It’s just a matter of doing it.

  6. llewelly
    January 8, 2013

    What about Chasmaporthetes ? Byers always mentions Chasmaporthetes in his hypothesis. But other people mostly focus on false cheetahs. Why?

  7. Ross Barnett
    January 9, 2013

    Great article! And not just cos Im mentioned in it. Strangely, stable isotope work has been done on Miracinonyx from NTC (See McNulty et al. Palaios 17:1) but with an emphasis on diagenesis. Still the results did suggest a predator-prey relationship between pronghorn and Miraicinonyx.

  8. Donald Prothero
    January 9, 2013

    The fossil record of Antilocapridae is actually quite good (although a taxonomic mess) and goes back to the early Miocene. The earliest pronghorns were ALWAYS long-legged, always the most cursorial of hoofed mammals. I would argue that the were specialized in running from ALL predators, not just the last predator to be a specialized runner.

  9. John-Paul Hodnett
    January 9, 2013

    Thanks for acknowledging our work, Brian. FYI, we have fossilized big cat dung from one of the caves where Miracinonyx occurred in the Grand Canyon which is awaiting analysis.

  10. J. S. Lopes
    January 9, 2013

    Pronghorns would suggest that lions and tiger could be brought to New York and Los Angeles to reinvigorate the evolutionary competition that gave humans reason to become smarter.

  11. John-Paul Hodnett
    January 9, 2013

    Adding a little more for food for thought….

    The occurrence of pronghorn with Miracinonyx is true for Natural Trap Cave, but there is a greater number of big horn sheep, stout legged horses, and other more upland critters at that locality.

    Living Iranian Cheetahs live differently than their iconic African cousins, which instead of living in the savannas typically seen for the “cheetah model” they live in arid highlands, hunting mostly wild sheep and upland antelopes.

    In the Blancan of Arizona and the rest of North America, at least you do see a higher degree of association of Miracinonyx with Antilocaprids (like Capromeryx, which was a bit bigger then), along with the hunting Hyena Chasmaporthetes.

    I think when it comes right down to it its hard to say what influenced the evolution of Antilocapra as many of its close kin during the Pleistocene and older where more stoutly built and were probably not the speed demon that the modern pronghorn is.

  12. Brian Switek
    January 9, 2013

    Thanks for the comments, everyone, and for the additional references, John-Paul. I had not seen the McNulty et al. paper. The literature on Miracinonyx seems rather sparse, which is why I was befuddled that so much has been made about its supposed habits. I look forward to seeing more details about the Grand Canyon cats!

  13. Mary C. Carpenter
    January 9, 2013

    Nice to see our work referenced! John-Paul, kudos to you for all your hard work. Looking forward to seeing more on this topic.

  14. Richard White
    January 9, 2013

    The trouble with this old “arms race theory” is that pronghorn developed into cursoral animals long before there were any felid pursuit predators around – it is much more likely that they developed long legs and speed as a response to the patchy, widely separated distribution of the plants they fed upon.

  15. Richard White
    January 9, 2013

    I would say that Don’s comments apply fairly well to the antilocaprinae, which likely took advantage of the long legs and speed they inherited from their “merycodontine” ancestors, but that the evolution of long-legged cursorial ability in the “merycodontines” was more about resource distribution over the landscape and moving quickly and efficiently from place to place, and less about escaping pursuit predators.

  16. Richard White
    January 9, 2013

    The record of Pleistocene Antilocapra is very poor indeed – as I recall, there are around 30 or 35 such records in the literature, but as I looked at them, only 2, I think, were based on diagnostic horn cores – the NTC population, and two specimens from California. Other than that, the records are based on scraps and pieces, often only fragments of bones, with no wat to differentiate them from either Stockoceros or Tetrameryx. Compared to the Holocene record, the modern pronghorn is rare in Pleistocene deposits.

  17. Eli
    March 20, 2014

    This animal has always been one of my favorites. Please write an article if anything else in discovered!

  18. David Marjanović
    March 28, 2014

    Oreamos

    Oreamnos.

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