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Pronghorns

The second fastest land mammal is the pronghorn (Antilocapra americana), a delicate artiodactyl which ranges across the western wilderness of North America from Canada to the Baja deserts.  Although they look similar to antelopes, pronghorns are actually the last surviving species of the family Antilocapridae. They can run at speeds of up to 60 miles per hour and (unlike impalas or cheetahs) they can run at full throttle for a fair distance.

The Range of the Pronghorn

Pronghorns are named for their forked horns—which are not antlers but true horns made of bone with a layer of keratin.  They shed the hollow outer sheaths each year in late autumn and grow a new pair over the winter. Adult pronghorns stand 90 cm (three feet) high at the shoulders and weigh up to 50 kg (110 pounds).  Although pronghorns can run swiftly, they are poor jumpers.  Herds of pronghorns make great migratory treks across the country and face pressure from human developments and from fences (which they can’t jump over but must run under).  If you are a rancher in pronghorn country you might consider putting a non-barbed strand of wire as the bottom wire on your fence.

 

Two Pronghorn Bucks

Pronghorns once had many close relatives.  The Antilocapridae family is most closely related to giraffes but the different family members filled many of the same niches that bovids do in the old world.  These animals came in an array of shapes and were widespread across North America. There were once 22 varieties of antilocapridae (which you can explore here) but they died out ten to fourteen thousand years ago when the Clovis hunters arrived and slaughtered North America’s megafauna.

The distinctive head of Osbornoceros

Sick or injured pronghorns are sometimes preyed upon by wolves, coyotes, or cougars, but when they are healthy, adult pronghorns can easily outrun all contemporary North American predators. Their blazing speed is not an evolutionary extravagance: pronghorns once needed their swiftness to escape Miracinonyx trumani, the American cheetah which could probably run nearly as quickly as the living African cheetahs.  Like the avocado the pronghorn was molded to fit an ecosystem which has died out: today they are literally running from ghosts.

An American Cheetah Hunting a Pronghorrn

 

The Giant Armadillo (Priodontes maximus)

We boldly continue armor week with an overview of the magnificent armadillo family.  This order of armored mammals (Cingulata) is more diverse than any other sort of armored mammals–outshining even the scaled pangolins. Today the only living members of the Cingulata order are the armadillo family (a successful group consisting of more than 20 living species) but the armadillos’ extinct cousins were once far more widespread and bizarre.  These relatives included the pampatheres–long plantigrade browsing creatures covered in banded armor who roamed the continent from one end to the other.  Even more impressive were the glyptodonts, massive tank-like creatures bigger than a compact car.

A fossil glyptodon, fossil pamphathere, and armadillo skeleton (in the far right corner)

The Cingulata order is part of the superorder Xenarthra. Separated from all other placental mammals for over 100 million years (due to South America’s unique isolation after the breakup of the southern supercontinent Gondwana), xenarthrans evolved in different directions from other mammals. The unique challenges and opportunities of their island continent resulted in bony domed giants like the pampatheres and glyptodonts, both of which are characterized by tortoise-like body armor composed of bone segments (osteoderms).  The glyptodonts were unlike tortoises in that they could not draw their head beneath their shells: instead their heads were protected by bony caps atop their skulls. The largest glyptodonts could grow to 4 metres long, 1.5 metres high and have a mass of 3 tons (Ferrebeekeeper has already written about the smallest known Cingulata species—the pink fairy armadillo, which can still be found living in the central dry lands of Argentina).

Glyptodon

Thanks to convergent evolution the herbivorous glyptodonts resembled other armored giants like cryptodire turtles and ankylosaurs.  One species of glyptodont, Doedicurus clavicaudatus, even had a heavy spiked tail (although it is unclear whether this was used against predators or to compete for territory and mates).

Doedicurus clavicaudatus

When the first members of the Cingulata order emerged in the Myocene, the top predators of South America were giant running predatory birds–the Phorusrhacidae, which resembled giant dashing eagles up to 3.2 metres (10 ft) high.  The glyptodonts, pampatheres, and armadillos outlasted these terror birds and they then outlasted the carnivorous metatherian mammals (with terrible saber teeth) which followed.  When the Isthmus of Panama connected South America with North America (and therefore with an entirely new universe of ultra-competitive mammals), the armored cingulatans competed just fine with the newcomers.  Some glyptodonts and pamphatheres wandered up through Central America and found new homes in North America.  The armadillos are still there.  However at the end of the last ice-age, a new African species arrived and brought a devastating and final end to the glyptodonts, the pampatheres, and most of the armadillos. But even this newly arrived predator seemed impressed by the greatest of armored mammals.  An Argentine anthropologist even reports discovering a site twenty leagues from Buenos Aires where early human hunters had used glyptodont shells as dwelling places.

Human Hunters Stalk a Glyptodon (Heinrich Harder)

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