The spectacled bear and its spectacular forebears

Earlier this year, we spotlighted a video of a spectacled bear ambling through the terraced ruins of Machu Picchu. If you haven't watched it, now's your chance: it's not every day you get to see a bear paying a visit to one of the most iconic archaeological sites in the world (and look out for the llama eyeballing its four-legged competition at about 1:02).

The spectacled (or Andean) bear – which turns out to be more common around Machu Picchu than previously believed – is the only South American bear, found in the ranges of the Andes from Venezuela in the north to Peru and Bolivia in the south.

But the species isn't unique just for being the only bruin on a huge continent: it's also the sole remaining representative of a bear family that once encompassed some of the all-out most formidable mammals ever to exist.

Tremarctine titans

We're talking about a corner of the ursine family tree called Tremarctinae: the "running bears" or "short-faced bears". Neither of those descriptors is altogether accurate, based as they are on what may be a shaky understanding of perhaps the best-known of the extinct tremarctine species: the giant short-faced bear, Arctodus simus, which thumped around North America from about 1.8 million years ago to 11,000 years ago.

“The spectacled bear is the sole remaining representative of a family that once encompassed some of the all-out most formidable mammals ever to exist.”

A. simus without question ranks as one of the biggest terrestrial carnivores of all time, alongside its tremarctine relatives: the South American giant short-faced bear (Arctotherium angustidens) and the huge African short-faced bear (Agriotherium africanum).

A male North American giant may have tipped the scales at well more than a ton, towering 5.5 feet or more at the shoulder, and rearing imposingly on its hind legs to nearly ten feet tall.

Arctotherium angustidens, the biggest of five Arctotherium species known from Pleistocene South America, may have been even larger: as much as 3,500 pounds!

The heft of these vanished relatives makes the spectacled bear look like a pipsqueak, although of course a 400-pound animal – the size of an especially large male Andean bear – is plenty big by modern standards.

A rough place to live

The giant short-faced bears of the Americas outsized any other carnivores of their time. North America in particular once hosted a pretty staggering roster of toothy beasts: in the words of biologist Valerius Geist, a "predator hellhole" greeted human beings as they crossed over to modern-day Alaska from Siberia. We're talking cheetahs and American lions (bigger than any modern big cats); the saber-toothed cat Smilodon and "scimitar-toothed" cat Homotherium; running hyenas and dire wolves. And let's not forget the grizzlies, gray wolves, wolverines and other survivors of the megafaunal extinctions that helped close the latest Ice Age.

Standing head and shoulders above this roaring and snarling gaggle was A. simus. Its exact ecological role, though, has been the subject of much debate. In this respect it resembles another of prehistory's great monsters, good old Tyrannosaurus rex. Palaeontologists have long debated whether the "tyrant lizard" was a terrifyingly active predator or a (still admittedly terrifying) scavenger.

The same controversy exists for A. simus, with a third potential lifestyle thrown into the mix: the omnivorous route taken by all modern ursids save the polar bear. Some have suggested the giant short-faced bear was a fast-running predator of ungulates, although the widespread idea that the species had longer legs than other bears has been questioned in recent years. (Same goes for the "short" face, although tremarctine bears do have a broader mug than some of their modern cousins.)

Other scientists suspect A. simus was a carrion-eater, and perhaps functioned as a kleptoparasite. They see the bear using its towering height (and sense of smell) to detect carcasses, its dogged pace to reach them, and its colossal size to send packing whatever brought down the meat in the first place – lion, saber-tooth, wolf and the like.

The giant short-faced bear of North America may have tipped the scales at well more than a ton, towering 5.5 feet or more at the shoulder. Image: Image: Martin Cathrae/Flickr

Though the classic image of the beast places it on the Ice Age "mammoth steppe", we now know the bear ranged into what's now the southeastern United States, including present-day Florida, where it rubbed shoulders with tremarctine cousins like the Florida spectacled (or cave) bear. That means the titanic creature haunted not just open subarctic grasslands but also woodlands and forests. In such environments, the bear may have happily included plant food on its menu in addition to meat.

A 2010 journal article suggests omnivory as the sturdiest interpretation of the giants' dietary ways, but it also notes that short-faced bears of northern tundra and grasslands may well have been mainly meat-eaters – and with their scavenging tendencies, they might have benefitted from sharing the landscape with saber-toothed cats. Over-the-top fangs and a relatively weak bite likely made the bulky saber-tooth quite a specialised feeder, adapted for slicing flesh rather than chomping and crushing. That means the cat probably left behind ample meat and all the marrow-rich bone on its kills, providing plenty of spoils for the more powerful jaws of the short-faced bear.

It seems safe to conclude that the giant short-faced bear was, at the very least, a figure held in healthy respect by North America's colonising human beings – and quite possibly the most intimidating beast they had to contend with. It's even been suggested that bears and other formidable New World carnivores such as the American lion may have stalled or rerouted human expansion into the continent.

Naturalist and grizzly-bear expert Doug Peacock points out another possible legacy of North America's crowded Pleistocene predator roster. The grizzly bear (Ursus arctos horribilis), a subspecies of the brown bear, is generally a more aggressive and hot-tempered bruin than its Eurasian relatives – and some speculate that disposition has to do with coming of evolutionary age on the Ice Age steppes of North America.

In the wide-open barrens of those fraught times, a mother grizzly had to defend her cubs from lions, wolves, sabertooths and, yes, short-faced bears. The result? Possibly a more irascible version of the brown bear.

"It might be informative to examine the possibility that Pleistocene North America might have been an unusually rough place to live," Peacock writes.

Sole survivor

Easily romanticised and unquestionably impressive, the giant short-faced bears are plenty dramatic. But that shouldn't take anything away from the spectacled bear's own charms.

This most arboreal and herbivorous of bears inhabits a remarkable spread of habitats on the shoulders of the Andes, from the coastal desert of Peru to the cool páramo grasslands above the timberline. We're talking better than 14,000 feet of elevational range for the species.

Its quintessential habitat is the cloud forest, that moss-cloaked high jungle that reaches its zenith along the eastern slope of the Cordillera Oriental, between about 3,000 and 9,000 feet.

A bit like South America's version of a great ape, the roughly gorilla-sized bear splits its time (gorilla-like) between forest floor and canopy, pulling itself up tree trunks and thick lianas. Mostly a plant-eater, it has a love for fruit, smashing down ripe branches too flimsy to support its weight.

When soft, juicy fruit isn't available, spectacled bears employ massive jaw muscles – rivalled among bears only by the giant panda – to munch tougher, more fibrous greenery. They've also got a strong taste for bromeliads: one local name for the creature, oco achupayero, means "bromeliad-eating bear".

But like all bears, this one won't turn up its stubby nose at animal protein. Insects, small mammals, carrion, even the occasional meat on the hoof – cows grazing on mountain pastures, for instance.

That taste for livestock sometimes brings the bears into conflict with human neighbours (as does their occasional fondness for munching corn and other cultivated crops).

Mitigating such conflict with people is essential for the conservation of the species, especially since the impacts of climate change on bear habitat and food sources appear to be heightening bear-human tensions in some areas.

In the interest of the carnivores and local livelihoods alike, one Bolivian biologist, Ximena Velez-Liendo, is helming a project aimed at reducing cattle losses to bears. Her initiative was recently announced as a finalist for a Whitley Award, the so-called "Green Oscars" that help fund conservation projects in the developing world.

Protecting the spectacled bear is important work, not least because of its ecological significance. "The spectacled bear is well-qualified to serve as an umbrella species for biodiversity in the Andes and in the world," explains biologist Bernard Peyton, noting how many endemic organisms fall within the bear's range. Safeguarding the future of the species in the Andes, therefore, helps to preserve whole ecosystems of outstanding biodiversity.

So we've got plenty of reasons to care about the spectacled bear: its own intrinsic worth (same as any creature) and the wide-ranging habitats it knits together in its foraging. And, lest we forget, the fact that this placid plant-eater is the only living link we have to a very grand pantheon: the mighty short-faced bears of yore, vanished titans that – like T. rex – can still evoke not a little fearful awe in our imaginations.