Laelaps

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A grizzly bear (the black dot in the middle of the photo) walking near the treeline in Yellowstone’s Hayden Valley.

ResearchBlogging.org

The quiet of my evening wildlife watching was suddenly broken by a thick Boston accent. “Oh my gawd! Look! It’s a grizz! That’s the last animal I needed to see! It’s a grizz!”

He was right. Lumbering across the valley was a big dark shape that could only be a bear. It was not very close, being little more than a dot moving along the distant treeline, but through the zoom lens of my camera it was just possible to make out the hump that distinguishes black bears from grizzly bears. It was the closest I would get to Yellowstone’s largest predator during my visit to the national park (at least that I know of), but in the not-too-distant past an even larger cousin of the grizzly roamed much of North America.

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Three visions of the short-faced bear: Arctodus as a predator, a scavenger, and an herbivore. By Oscar San-Isidro, from Figueirido et al., 2010

Arctodus simus, the short-faced bear, was part of the recently-lost Pleistocene megafauna which disappeared from this continent around 11,000 years ago. The first human inhabitants of this continent undoubtedly encountered it from time to time, and the prospect of meeting a bear which stood five feet at the shoulder is a chilling one. It was the epitome of the big, bad bear, but just how bad was it? As argued by paleontologists Borja Figueirido, Juan Perez-Claros, Vanessa Torregrosa, Alberto Martin-Serra, and Paul Palmqvist, the popular image of the short-faced bear as a hypercarnivorous superpredator may have obscured the reality of the beast.

There are a few things that “everyone knows” about Arctodus: that it was short-faced, had long limbs, and was more carnivorous than living grizzly bears. Its long limbs, especially, have been taken as evidence that it ran down its unfortunate prey, though it would not have been above running dire wolves or saber-toothed cats off their kills, either. From time to time some researchers have proposed that Arctodus was an omnivore that scavenged more than it hunted, and one study even hypothesized that it largely relied on plant food, but the vision of the bear as a highly-predaceous carnivore has remained the most popular.

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A comparison of the skull of Arctodus (top), a black bear (2nd from top), a grizzly bear (third from top), and a polar bear (bottom). From Figueirido et al., 2010.

When Figueirido’s team re-examined the anatomy of Arctodus and compared it to a variety of other carnivores (a total of 411 individuals from 57 species), however, they found that the short-faced bear had much more in common with living omnivorous bears than had been previously appreciated. Even though its short jaws and long limbs had previously been used to suggest that Arctodus was similar in habit to feline predators, it turned out that it was not that different from living bears in the proportions of its face and limbs. While Arctodus had a deeper snout, for example, the length of its face was not significantly shorter than what is seen among its living cousins. It was not really a “short-faced” bear at all.

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Three restorations of Arctodus, revealing the skeletal, muscular, and external anatomy. By Oscar San-Isidro, from Figueirido et al., 2010

The details of the arms and legs of Arctodus are a little more complicated. Its limbs were not as long as would be expected if it were a high-speed-pursuit predator, but, for its size, Arctodus had longer and more slender limbs than would be predicted according to the relationship between limb length and size seen in other bears. Maybe it had a little more speed than modern grizzlies (which can run faster than you can), but it did not have the anatomy for cheetah-like sprinting, either. Furthermore, the authors suggest that the image of Arctodus as long-legged may be a sort of optical illusion caused by its short back. The skeletal proportions of the bear are different from those of cats and dogs, and so it looks a little more leggy than it really is. (This is true of skeletons of extant bears, as well. Most people are familiar with stuffed mounts of bears from showrooms and museums, but few have seen a skeleton of a bear, which in my opinion also look a deceptively long-legged.)

But what about the isotopic studies which have supported the idea that Arctodus preferred meat? Isotopes of elements such as oxygen, carbon, and nitrogen have been used to determine what sort of food animals ate and what environments they lived in, and studies of isotopes in Arctodus remains have suggested that it was primarily a carnivore. As the authors of the new study note, however, the bears on which these studies have been carried out have been especially large individuals from Alaska. Perhaps they, like living Kodiak bears, ate more flesh than their smaller counterparts that lived further south in the continent. If this is correct then the habits inferred on the basis of the bears from Alaska might represent only those populations, or perhaps only those particular individuals, and cannot be used to create a blanket statement about how all Arctodus behaved. In general, Arctodus appears to have been similar to extant omnivorous bears in habit (and perhaps regional variability), leading the authors to conclude:

In short, we suggest that A. simus may be best envisaged as a colossal omnivore whose diet probably included varying amounts of meat according to food availability. Of course, we do not wish to imply that A. simus did not prey occasionally on bison, deer, or ground sloths, nor that it did not scavenge the carcasses left over by the hypercarnivores such as saber-tooth cats (Smilodon fatalis and Homotherium serum), giant lion (Panthera atrox), and dire wolf (Canis dirus). We simply affirm that A. simus did so in a similar manner as some North American populations of brown bears (e.g., Alaska and Yukon) currently do so.

Rather than representing mutually-exclusive alternatives, then, the restorations of Arctodus by Oscar San-Isidro envision different aspects of its feeding habits. Unlike the big cats of its time it was a generalist feeder that could subsist on a variety of food sources and exploit the leftovers of other predators. Perhaps some individuals or populations were more predatory than others, distinctions that will require further study to determine, but even if it was not a rapacious carnivore I still find Arctodus every bit as fascinating.

Figueirido, Borja, Pérez-Claros, Juan A., Torregrosa, Vanessa, Martín-Serra, Alberto and Palmqvist,, & Paul (2010). Demythologizing Arctodus simus, the ‘Short-Faced’ long-legged and predaceous bear that never was Journal of Verterbrate Paleontology, 30 (1), 262-275 : 10.1080/02724630903416027

Comments

  1. #1 Dave Hughes
    February 2, 2010

    If it really was a generalized omnivore like the living bears, this raises the question of why it isn’t still around? If Arctodus was a specialist predator or scavenger of large mammals, then its extinction along with the rest of the Pleistocene megafauna makes some sort of sense. But if it could get along just fine on roots, berries, nuts and the odd bit of meat, just like its modern cousins, then you’d think that Holocene North America would still be well able to support it?

    I muust admit though, my main problem with this new paper is an emotional one: I just WANT to imagine Arctodus as a huge, mean superpredator. It’s so much cooler that way!

  2. #2 J.S. Lopes
    February 2, 2010

    Could be his arms used to grasp branches, like giant sloths, giant short-faced kangaroos (Sthenurus) or chalicotheres? If it was a colossal omnivore, could we immagine it in a way of life similar to geladas’ or chimps’?

  3. #3 Cameron
    February 2, 2010

    Dave Hughes #1

    why it isn’t still around?

    This species was one of the last megafaunal species to go extinct as it lived until the Pleistocene/Holocene transition.

    Schubert, Blaine W. (2010). Late Quaternary chronology and extinction of North American giant short-faced bears (Arctodus simus). Quaternary International. In Press.

    This coupled with its generalizations make me suspect that humans played some role.

  4. #4 David
    February 2, 2010

    cool post, thanks.

    Were his long limbs protected under his right to bear arms?

  5. #5 George Davis
    February 2, 2010

    I strongly suggest you take a look at the site for Riverbluff Cave. Owned by the City of Springfield Parks and Recreation department in Missouri, it has evidence of the short-faced cave bear:

    http://www.riverbluffcave.com/gallery.php?rec_id=104&link_id=32

    among other species. A real Pleistocene mix of species. Worth a look. The geologist in charge is Matt Forir, who does really good work.

  6. #6 tai haku
    February 2, 2010

    I would second Dave’s question. A truly adaptable omnivore would, one would think, survive the megafaunal extinction. If human persecution was at hand then why did we lose the short-faced but not the grizzly which was at the time of columbus’ arrival doing pretty well across the continent I think?

  7. #7 Mal Adapted
    February 2, 2010

    I propose the following scenario: surely the first human colonists of North America were mightily impressed by Arctodus. It’s not hard to imagine them saying to one another, “Let’s kill as many of these monsters as we can, as quickly as possible, or we’ll never be safe here!”

    If the first Americans caused, or contributed to, the extinction of other megafauna by hunting, why not Arctodus?

  8. #8 Laelaps
    February 2, 2010

    Thanks for the comments, everyone.

    JS; Interesting idea, but I don’t think Arctodus is a good gorilla/chalicothere/sloth analog. At 12 feet tell when standing up, it definitely could have reached at least the lower branches of some trees, but anatomically it was quite different than the animals you mentioned. Overall I think omnivorous bears are probably better models.

    As for the idea that Arctodus should have survived the Pleistocene mass extinction, I am not so sure we can safely assume it lends support to the overkill hypothesis. Obviously there are still niches occupied by equids despite their extirpation, and mammoths, lions, and sloths could probably survive in places in North America today (or, at least, that is what advocates of Pleistocene rewilding say), and I am not sure humans can account for all the extinctions of large animals. As has been mentioned, different animals died off at different times, some persisting thousands of years longer than others, and I think that (as has been said in the literature) we are going to need to cultivate a more comprehensive understanding of the natural history of end-Pleistocene victims and survivors to start before we can determine the roles possibly played by humans, climate, etc. It is tempting to assign particular patterns to a given extinction trigger, but right now I think that we just don’t know enough to draw firm conclusions.

  9. #9 Mal Adapted
    February 2, 2010

    Thinking a little more about the interaction between Arctodus and early humans, how does this sound:

    If Arctodus commonly drove other predators off kills, it would have done the same thing to humans. It would not have expected serious challenge when doing so. Rather than being driven off, however, the humans may have backed away to a safe distance and allowed Arctodus to claim the kill, then thrown spears, perhaps with atlatls, to kill the bear. Grizzlies, being sub-dominant to Arctodus, may have been more cautious with humans at the outset. In other words, Arctodus‘s aggressiveness and fearlessness may have made it uniquely vulnerable to humans, in a way that grizzlies weren’t.

  10. #10 Raymond
    February 2, 2010

    -Mal Adapted

    The problem with that scenario is that not every bear would have been killed. If just a few females survived their encounters and went “whoa! These weird bipedal critters are dangerous!”. They would have passed that on to their offspring and resulting lineages would quickly replace the stupider bears.

  11. #11 John McKay
    February 3, 2010

    Raymond,
    That’s a common misunderstanding about the overkill theory. It’s not necessary for humans to kill every member of species. We only need to kill them faster than they breed. Big animals are most vulnerable to overhunting because they breed slowly and exist in smaller numbers.

  12. #12 Dave Hughes
    February 3, 2010

    Fascinating dicusssion, but as frustating as ever. It’s just too easy to come up with “what if?” scenarios that sound perfectly plausible but are untestable and therefore don’t take us any further. The solution is obvious. We just need to find some high-quality Arctodus DNA from remains preserved in the Alaskan permafrost, clone it, patch it into the egg of a South American spectacled bear, implant it, wait for the cub to be born and grow to maturity, then go into the bear’s enclosure with a bloody steak in one hand and a bunch of berries in the other. The bear’s chosen dinner will settle the debate. Any volunteers??

  13. #13 Bill;www.wildramblings.com
    February 3, 2010

    There is too little evidence to draw a conclusion as to why this huge bear became extinct. Better we all keep an open mind and hope that more facts are found that will help us to discover the cause of its demise.

    A great, thought stimulating article,thank you.

    Bill;www.wildramblings.com

  14. #14 Cameron
    February 3, 2010

    Oh jeez, I just realized that Schubert (in press) claimed that a propensity for meat in A. simus may have caused competition with Clovis culture humans! It’s odd that a peer-reviewed article like that could overlook the 15 years of research following the last study suggesting hypercarnivory…

    Maybe it had a little more speed than modern grizzlies

    Maybe, but the proportionally long humerus and femur are the opposite condition of what is found in cursory mammals. It looks similar to human leg proportions, so they could have also been slow-but-efficient locomoters. This has been brought up from time to time in publications but never studied as far as I know. I’m particularly curious as to why A. simus still has a radial sesamoid…

    It seems that A. simus is always depicted in open country, but I have only seen specimens having been recorded from caves. If they actually did live mostly in plains, this could have made them more vulnerable to humans. Of course (as I should have made more clear before), humans probably played some role, although certainly multiple factors were at play.

  15. #15 Raymond Minton
    February 7, 2010

    While I have to say the idea of Arctodus as a super predator is more attractive, the more conventional “bear like” depiction of more recent research is more plausible. I’m sure this behemoth had it’s moments of carnvory, and I can easily see it taking down a bison with a swipe of it’s paw. A fascinating animal in any case, since nothing exactly like it remains in the modern world.

  16. #16 Peggy Richter
    February 15, 2010

    I tried to look at the article, but the link appears to be broken. Some rank beginner’s questions:
    1. the comparison is to black bear, grizzly and polar bear. But wouldn’t it have made sense to compare to the panda (a bear relative that IS a known plant eater) or even the Asian black bear?
    2. The build reminds me of a Bouvier des Flandres. These aren’t the fastest dogs around, but they can and do have a very good endurance, agility and can pack plenty of punch (their role as dogs is herding and protection work). It isn’t necessary to be as fast as a cheetah if you can outlast the deer you are chasing at a slower but longer-maintained pace.
    3. It seems the objection has been made about the diet being based on Alaskan examples without others — fair enough, but there doesn’t seem to be anything that indicated any evidence from other finds to counter the Alaskan examples.
    vr, Peggy Richter.

  17. #17 Laelaps
    February 16, 2010

    Peggy; Sorry about the link. I don’t know why it isn’t working. You can get the article, free, here – http://www.informaworld.com/smpp/content~db=all~content=a918962183

    1 – The scientists compared the skull of Arctodus to many other bears. I just had to cut the diagram for length.

    3 – As mentioned above, and in the paper, there appears to be a size difference between the bears from Alaska and the lower 48. This is similar to the size difference between living grizzlies across those ranges, and while more research needs to be done I still think it would be interesting to look into this question. The authors did not say that they definitely know the different populations had different feeding habits, but that we should be careful about issuing blanket statements about entire species over a wide range when what we know about them comes from only a few individuals from one area.

  18. #18 Dennis
    June 21, 2010

    There is way too much to be learned about why the great beasts became extinct. The most common land animal at the time was the horse. Certainly humans did not kill off them by the millions. Something else came into play and whatever did this certainly did this to the specialized carnivores of the time, American lion, Smilodon, Dire wolf, and probably Arctodus. Concrete proof is needed. Humans certainly did kill much of the mammoth population, but a bigger piece of the puzzle is missing. Could humans wiping out mammoths changed the landscape? Elephants eat grasses. Would trees overtake the land if no elephants and less grazers were around?

  19. #19 Dennis
    June 21, 2010

    Humans wiped out the most land-altering animal – the mammoth. When that mammal’s numbers dwindled, the trees took over. Therefore, North America’s landscape offered a differed food source for the animals remaining (i.e. the horse) and they couldn’t adapt. With their numbers down, specialists died off. Sound good?

  20. #20 Steven
    October 22, 2010

    As the climate became warmer, other species of bear and other animals were free to expand throughout the northern continent. Imagine how much of an area Arctodus would need. These were great solitary beasts. They would be competing with more bear species, more carnivores, more scavengers, more onmivores, and more humans. They would also be competing with other short-faced bears. When I first learned of Arctodus, he was just one of many megafauna that didn’t survive global climate change. Today polar bears are facing the same problems short-faced bears did 11,000 years ago.

  21. #21 Toby
    October 29, 2010

    From what I have read, Arctodus simus was taller, but not as heavy as coastal brown bears or polar bears. Brown bears, such as the grizzly seldom kill large herbivores such as adult moose or bison. I doubt that the short-faced bear did either. However, just as the brown bears will take a kill from other predators today, Arctodus simus likely took meat from wolves, lions, and Smilodon.

  22. #22 film izle
    November 1, 2010

    I propose the following scenario: surely the first human colonists of North America were mightily impressed by Arctodus. It’s not hard to imagine them saying to one another, “Let’s kill as many of these monsters as we can, as quickly as possible, or we’ll never be safe here!”

  23. #23 Derrick Ford
    November 10, 2010

    Hey, I have a question and the question is that. Why do short-faced bears have big bodies and small noses?

  24. #24 Bill Wadsworth
    November 25, 2010

    Check out Jake Page’s 2000 mover ‘Cavern’ for an optimistic look at Arctodus simus.

  25. #25 film izle
    November 27, 2010

    The problem with that scenario is that not every bear would have been killed. If just a few females survived their encounters and went “whoa! These weird bipedal critters are dangerous!”. They would have passed that on to their offspring and resulting lineages would quickly replace the stupider bears.