Midwestern Mammoths and Mastodonts: The M-cubed project
Note: This is the first post in a series focused on a 4-year, National Science Foundation funded project to look at the extinction of Mammoths and Mastodonts in the Midwest.
For the last few years we’ve been traveling…a lot. We started a project in 2011 to better understand 1) when mammoths and mastodonts went extinct, and 2) the ecological mechanisms that might have played a major role in how they went extinct. The major foundation of this project is a museum-by-museum survey of mammoths and mastodonts in collections from nine states and one province (MN, WI, IA, MO, IL, IN, OH, KY, MI, and ON). Over the last 2.5 years, we’ve documented mammoths and mastodonts from 576 localities.
When we started this project, we knew that the Midwest was a hotbed for Pleistocene proboscideans. A compilation of known/published localities showed a continent-wide distribution, but definitely a concentration in the Great Lakes. Of course, as with most things paleontological, the best represented individuals are the youngest, and both genera overlap with the first humans in to the New World. The last standing mammoths on the continent are widely separated in space, found from the South Dakota Badlands to upstate New York. After the last-glacial maximum, mastodonts seem to be limited to forested areas of the Great Lakes region and Northwestern North America.
Mammoth and mastodont studies lie at the intersection of major research questions in a number of different disciplines. The reason that they are so important is primarily due to the fact that they are so common and widespread in the fossil record. Why, you ask? Probably size and distribution. Their remains are big enough to be seen from the cab of a tractor or backhoe, and were distributed coast to coast during the last half of the Pleistocene. Since they are relatively widespread and common components of the fossil record, we can get an elephant’s eye view of ecological changes, IF we know what questions to ask. Their remains are also much more common in museum collections than other victims of the terminal Pleistocene extinction event, so they might give us a glimpse into HOW the extinction occurred.
Why (Part I): Preposterous Proboscidean Paradigm Shifts
The 2005 discovery of a mammoth tusk in the bed of Sugar Creek (central Illinois) started it all. Dennis Campbell, biology professor at Lincoln College (and ISM research associate), had brought a class out to the creek to census freshwater mussels when Judd McCullum, (then a student in the class), stumbled across a large cylindrical object. Despite good-natured ribbing that it was “just a tree trunk”, Judd was convinced it was a mammoth tusk…and he was right. ISM paleontologist Jeff Saunders identified the tusk as a woolly mammoth. Conventional thinking had woolly mammoths in Illinois at the same time as the glaciers. We thought that they occupied the narrow band of tundra in front of the massive continent-grinding glaciers that covered the Midwest up until ~18,000 years ago.
To be thorough, Jeff submitted a sample for radiocarbon dating anyway. The results were surprising. Rather than dating to the time of the glaciers, the Lincoln College mammoth dated a few thousand years later, when central Illinois was covered by a cold swamp, with black ash and spruce as the dominant vegetation, not a grassland. This was a game-changer. Not only were woolly mammoths found outside of their traditional tundra habitat, but when the glaciers left the area, they stayed and survived in changing Midwestern ecosystems until their extinction, ~12,000 years ago.
Meanwhile, a graduate student at the University of Utah developed an interest in the ancient DNA of North American mammoths. Jake Enk, now finishing his PhD at MacMaster University in Ontario, managed to extract a good chunk of mitochondrial DNA from the Huntington Mammoth in Utah. The Huntington mammoth is the epitome of a Columbian Mammoth. It’s from the heart of the Columbian mammoth range, Utah. It’s cheek teeth, although fairly worn (this animal was 55-60 years old), consist of 7+ enamel ridge-plates spread out into a relatively long tooth (~6 plates per 10 cm). For good measure, Enk also extracted DNA from two additional Columbian mammoth teeth from Wyoming. Surprisingly, when compared to woolly mammoth DNA from Alaska and Siberia, these Columbian mammoths were similar. Actually, they were VERY similar. The three Columbian mammoth mtDNA sequences nested nicely within one of the Alaskan woolly clades. The take home message was that morphological variability in mammoths is much greater than genetic differences. These were not separate species–they probably don’t even merit being a sub-species.
But mastodonts were not immune to paradigm shifts. In 2011, Neal Woodman and Nancy Beaven published a report on the dating of a mastodon in northern Indiana, the Overmyer mastodon. The date they reported was 1500 years younger than expected. The typical pattern was that mastodonts went extinct ~12,900 BP, only a few hundred years after the first major human cultural group (Clovis) appears on the scene. The Overmyer animal, if the dates were to be believed, meant that mastodons survived not only the first wave of human colonization, but lived side-by-side with human groups almost into the Holocene!
Studies like these got us to thinking. What if there are other assumptions about the habitat preferences and behaviors of mammoths and mastodonts that we are wrong about? What would happen if we dated more specimens–or used new techniques for insight into paleodiets and behavior (i.e., stable isotopes) or population dynamics (i.e., ancient DNA)? Was the Lincoln College Mammoth the exception? Or the rule? What do the major morphological differences between different mammoth populations mean if they don’t reflect relatedness–or evolutionary history? Did Mastodonts really hang on so late? Why was there such a large gap between the Overmyer mastodont and other dated animals in the Midwest? All of a sudden, there were a lot of questions that we didn’t know the answer to.
Why (Part II): Elaborate Extinction Scenarios needing Evaluation!
These questions are important not only for understanding past ecological conditions, but for understanding one of those BIG questions…why did 35 genera of North American megafauna (species >100 kg) go extinct at the end of the last Ice Age? This extinction event is considered one of the BIG 5 mass extinctions in the history of life on Earth. Yet it is unique from earlier mass extinctions. In addition to being the most recent, the majority of the victims were the largest of the large fauna. Small fauna were spared, more or less, or managed to migrate to new ranges. Furthermore, the extinction of these species coincided with major climate changes AND the introduction of a novel, supposedly predatory species known to profoundly alter its environment and potentially overhunt its prey, Homo sapiens. The discussion surrounding this extinction event in recent years has become increasingly polarized. There are a number of scenarios that have been proposed to explain this extinction. Perhaps some of the megafauna were killed off by colonizing human populations, with the rest doomed as the result of ecosystem reorganization after the loss of keystone species such as mammoths. Alternatively, abrupt climate changes may have stressed megafaunal populations to the breaking point. Deglaciation was not simply a gradual warming. The glacial spring came in stops and starts, and may have presented megafaunal populations with a moving target. Never quite able to adjust to changing conditions. These are the main working hypotheses, but of course, there are others. Was it the mid-air explosion of a comet over glacial ice in Canada? A hypervirulent disease? A combination of the above? It is hard to say without more hard data on the timing and ecology of key extinct species such as mammoths and mastodonts. Beware of TV documentaries claiming that we now know the answer to what caused these extinctions. Most scientists agree (although there a vocal few who don’t) that we don’t have enough data to tease out the smoking gun…let alone identify who or what pulled the trigger!
How (Part I): New Techniques
But how do you tackle something as big as megafaunal extinctions? This is a global pattern involving many different species and ecosystems. What sort of data do you need to distinguish between different extinction scenarios? Obviously, timing is everything. In the last decade or so, direct dating of megafaunal bones has become more accurate and commonplace. For this project, we’ve been dating a lot fossils from museums, trying to fill in the gaps in space and time. We hope to say something about when these animals ultimately went extinct using new and improved chronological datasets. We also believe that animal ecology is an important aspect of survival, so we are utilizing techniques that capture the details of individual life histories. Specifically, chemical signatures from bones and teeth (in the form of stable isotopes) that can tell us about animal diets and mobility. (more on what we are learning from these techniques in future posts)
How (Part II): The Team
Modern paleontology does not happen without a team of experts, each providing critical data for hypothesis testing. This project is a collaboration between many different experts. Jeff Saunders (ISM) and myself are vertebrate paleontologists/paleoecologists who are tasked with understanding biogeographic variation in space. Stacey Lengyel (ISM) is an expert in dating techniques–she also happens to be creating a great website on Ice Ace mammals that will be launched this spring. Greg Hodgins is a bone chemist and dating expert at the University of Arizona. J. Douglas Walker (University of Kansas) and Alan Walker (Iowa State University) are experts is different types of isotopic analyses. Others have also contributed to our understanding of proboscidean paleoecology. Veterinarian Dennis Lawler (ISM) has been instrumental in exploring the impact of disease on mammoths and mastodonts and Eric Grimm (ISM) has provided environmental context for dated specimens through his work on ancient pollen recovered from the mud of midwestern lakes.
As we scale back the data acquisition phase of this project and focus more on analyzing the datasets that we’ve collected, we’ll have more to say about how mammoths and mastodonts lived and died, at least across the Midwest. A significant component of this project is dedicated to communicating our results to the public, primarily through online resources like this blog and the aforementioned website. So stay tuned for future developments. The data have started rolling in.
Enk, J., Devault, A., Debruyne, R., King, C. E., Treangen, T., O’Rourke, D., … & Poinar, H. (2011). Complete Columbian mammoth mitogenome suggests interbreeding with woolly mammoths. Genome biology, 12(5), R51.
Saunders, J. J., Grimm, E. C., Widga, C. C., Campbell, G. D., Curry, B. B., Grimley, D. A., … & Treworgy, J. D. (2010). Paradigms and proboscideans in the southern Great Lakes region, USA. Quaternary International, 217(1), 175-187.
Woodman, N., & Beavan Athfield, N. (2009). Post-Clovis survival of American mastodon in the southern Great Lakes region of North America. Quaternary Research, 72(3), 359-363.