FOREIGN INVADER: Bison may have outcompeted other large mammals for resources.
Image: Eric Scott San Bernardino County Museum
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Bear-size beavers, mammoths, horses, camels and saber-toothed cats used to roam North America, but by 11,000 years ago most such large mammals had died off. To this day, experts debate what caused this late Pleistocene extinction: climate change, overhunting by humans, disease—or something else? Eric Scott, curator of paleontology at the San Bernardino County Museum in Redlands, Calif., suggests it was something else: namely, the immigration of bison from Eurasia.
Armed with data from his own ongoing excavations as well as from those dating back as far as the 1800s, Scott says that bison appeared in North America as early as 220,000 years ago and spread across the continent throughout the remainder of the Pleistocene, a time when climate change had made food and water scarce. He first formally suggested the idea last spring in the journal Quaternary International, speculating that bison may have won enough battles for food and water during that time to share the blame with climate change as the major cause of the large mammal extinctions.
Scott’s initial “aha!” moment came while excavating near the town of Murrieta, Calif., in the early 1990s. Years before, digging nearby in strata 760,000 years to 2.5 million years old, he had found no evidence of bison, only horses, and wondered: “What did horses think when bison showed up and ate their food?” So when his team excavated in late Pleistocene strata at Diamond Valley Lake near Murrieta, just miles away from where he had found no bison, and turned up fossils of bison and other mammals, he thought he might have an answer: “This brought home to me the idea that as bison immigrated into areas and their numbers grew, their effect on other large mammal populations might have reached tipping points.” Scott is now collecting data from other parts of the U.S. to make sure the pattern he has observed in the Southwest holds up elsewhere.
Scott speculates that bison would have had multiple advantages over other large herbivores. For example, their multiple stomachs probably allowed them to extract maximum nutrition from their food. And they need not have won every battle they engaged in. Instead they might have, for example, malnourished nursing mothers just enough to cause population collapse. With no large herbivores to eat, dire wolves, American lions and other carnivores would have starved as well.
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9 Comments
Add CommentSeems like the "aha" was based on pretty non-indicative "evidence." All good hypothesis has to start somewhere: but is this science, or just a very creative imagination of "what if?"
Reply | Report Abuse | Link to thisAs bison replaced the other large mammals, it would seem that large co-operative predators (lions, dire wolves, saber-toothed cats...) would have adjusted to "beef" as a food source. African lions do not have a problem taking large bovine prey.
Reply | Report Abuse | Link to thisHow you came up with a hypothesis doesn't have to be related to science. It's only when you go on to prove/disprove it that science comes into play.
Reply | Report Abuse | Link to thisWow, THE xuansu?
Reply | Report Abuse | Link to thisAnyway, that was my point exactly: Is Scott a scientist dreaming a hypothesis, or a dreamer hypothesizing about science? (I know you'll get the reference, even if nobody else does.)
donlb's thought occurred to me as well, but with some minor look-ups, I'm liking Eric Scott's idea.
Reply | Report Abuse | Link to thisIt turns out the dire wolves had shorter legs and were probably slower than the gray wolves that came from Eurasia.
A gray wolf pack has to run full-tilt to bring down a bison, so the dire wolves would have been less competitive in that hunting method.
The dire wolves could have been effective if there were enough of them to encircle a slower animal, but that requires a food supply big enough to support a large pack. Without enough food, the pack dwindles and the ability to hunt goes with it.
Even among gray wolves there are clearly lower limits for effective pack size, and lone wolves have a very hard time getting enough food.
Are the SciAm comment threads moderated?
Reply | Report Abuse | Link to thisI find them cluttered with off-topic advertisement.
TreeDiversity...that's what the report abuse link is for....
Reply | Report Abuse | Link to thisWell as Scott notes in the paper there is a lot of work to be done here, namely trying to gauge the abundance of bison in the fossil record and trying to get reliable dates for sites with bison fossils. I have a copy of the paper if anyone wants it.
Reply | Report Abuse | Link to thisBisons as the killers of big American game is rather an interesting idea, yet, than a scientific theory, but it is plausible, and Eric Scott seems to be on a good way to bring up further evidence.
Reply | Report Abuse | Link to thisI wonder why people criticize the preliminary character of his idea, who - most probably - have never done that with the other theory that it was men. Small groups of men, probably rather gatherers and gardeners than hunters? I think that this is much less plausible.