Scientists learn about animals long vanished from Earth by studying the bones they leave behind. Paleoecologist Kay Behrensmeyer talks about the secrets fossils have to tell!
Kay Behrensmeyer is a paleoecologist at the Smithsonian Institution in Washington DC…
And every year for the last 27 years, she’s scoured Kenya’s Amboseli National Park for remains of the dead.
Kay Behrensmeyer: … and sometimes we knew that a lion had killed a wildebeast, and we went to that place and marked the wildebeast bones with photographs and drill holes, and then we’d go back the next year and see what had happened and the next year, some of them even after 27 years they’re still little bits and pieces to be found. Mostly they’ve disintegrated, or been trampled to powder, but some of them have actually been incorporated into the soil, and look like they are going to start becoming fossils.
Behrensmeyer’s work is to reconstruct ancient ecosystems. In Kenya, for example, lions leave lots of bones lying around — while hyenas devour their prey, bones and all. She’s observed that populations of hyenas and lions change dramatically over just a few years. So the number of bones available to make it into the fossil record varies.
She says it’s a cautionary tale — if you reconstruct a moment in time from the fossil record, you can’t assume that’s the way things were a few decades later.
Kay Behrensmeyer: “Solving the puzzles that no one else has had a chance to solve is a real thrill, and that’s a great thing about being a scientist — that and being able to work with all the wonderful people I work with.”
Here are more extracts from the conversation with Dr. Behrensmeyer: more information about the lions and hyenas, how Dr. Behrensmeyer became a paleoecologist, and some final thoughts on bones.
Lions and Hyenas
In Amboseli National Park, there is a continual tug-of-war between the lions and the hyenas. When lions are plentiful, hyenas are scarcer. When lion population drops, the hyena population surges. Here’s what Dr. Behrensmeyer had to say about the effect on the bones.
Kay Behrensmeyer: One of my favorites is a long-term project studying how bones are preserved in an ecosystem in Africa. This is the Amboseli ecosystem. I started to study in 1975 and its still going.
And we’ve learned so much about the whole process of taking evidence from the hard parts of organisms that lived there, the elephants, the lions, all the other animals, the antelope, and watching how these change and become buried, and even fossilize in relatively short periods in time.
Watching any system like that over a couple of decades, you appreciate that there’s very little that’s really static in nature. Over decades, there are changes in the number of carnivores, the kinds of carnivores, the way the bones are being preserved, and this is real lesson for looking back into the fossil record. You may be able to reconstruct at that point in time. But you can’t assume it’s the same thing even after a couple of decades. The bones actually are turning out to be indicators of the kinds of predators, that is, hyenas versus lions that are dominant in the park. It used to be lions and there were lots of bones lying around because they don’t eat all of them. Now the hyenas have become much more dominant, we’re not exactly sure why, but because of all the hyenas there’s intense pressure to eat up all the bones. So we’ve seen a great change from many potential fossils on the landscape to actually now relatively few. And If it changes again, and goes back to lions being dominant, we hope to see if our potential fossils will come back.
It was obvious in the early nineties that the hyenas were having lots and lots of babies, and the babies were surviving and the lions were fewer. So the lions were less in evidence, so the hyenas had a chance, they compete usually, and when there are a lot of lions, the hyenas don’t do so well. But anyway the lions were gone, the hyenas started to proliferate.
When I went back in 2001, I heard that there were hyenas everywhere and we could see that, they were out during the day. And the other researchers in the park had noticed there were fewer bones. So I did some transects to sample, and I did that again in 2002. And sure enough, there were seventy-five percent fewer bones on the landscape, because of what we think of as this hyena effect.
If you see hyenas around a carcass, if you’re lucky enough to catch that in action, right now it’s just bedlam, it’s a feeding frenzy of great proportion, and there can be 30 or 40 hyenas around one large carcass, of a buffalo say and when they are finished with it there’s very little left.
How does one become a paleoecologist?
Dr. Behrensmeyer had to overcome several hurdles to get where she is now. As an undergraduate, she started off as an artist, but her love of the outdoors and of puzzles led her into geology. A field project in Wyoming studying a peculiar mixture of shark teeth and land animal remains got her interested in the field of taphonomy.
Kay Behrensmeyer: That got me interested in a field called taphonomy, which is the study of how fossils come to be. How animals, and plants and lots of other organisms can be preserved –and we know that they don’t all get preserved. So how is that little tiny sample in though fossil record representing all the life that was in the past? And that got me started on taphonomy, but taphonomy is really just the tool to reconstruct the ecosystems of the past, and that is paleoecology.
By good luck, I was able to get to East Africa to do my Ph.D. work, trying to figure out the environments and the human ancestors in the area of northern Kenya known as Lake Terkana. Also by good luck was able to find an early artifact site, that was one of the earliest artifact sites of that time. Humans had left these strange angular pieces of rock. When I saw these I had never done any archaeology, but I knew they weren’t natural geologic formations — they weren’t natural stones that you would expect to find in this kind of sediment. The site was named the KBS site after my name.
It was a real thrill, but that kind of discovery is not the only reason to be in a field like this. Its to be able to take different lines of evidence, from geology from paleontology from ecology and weave them together into a plausible, scientifically supported story about how these ancient ecosystems functioned. How animals, like the early humans, were able to live there, and the kinds of other animals they lived with and then how their bones got buried for us to find later on.
I think though, if I hadn’t had the opportunity to go to East Africa, where there was a lot of interest in human paleoecology, that maybe it wouldn’t have been as easy to convince my advisors in graduate school that this was a valid thing to do.
When I had one of my earliest meetings with my advisors, and this was at Harvard University, I said, “well I’d like to be interdisciplinary.” And they were skeptical. It was as if: “well, you’ll learn, it’s really hard to be interdisciplinary. You have to have one field you’re really good at or you’ll be considered a dilettante, or someone who isn’t really an expert at any one thing.” And I think now I appreciate that advice more than I did at the time. It just seemed like they were being a bit stodgy and conservative. To me it seemed there were so many wonderful connections to be made between fields, and that that was really exciting ground to develop a career in. But nevertheless, I was grounded in geology, and became a paleontologist in graduate school and took some biology courses and branched out in that direction. Subsequently my experience has been at the interface between geology, and paleontology, and paleoecology — a real conjunction.
I think my advisors were worried that I wouldn’t have a good solid foundation to get a job later on. And as it turned out, I didn’t get a job right away, but I was able to follow a lot of good leads for post-doctoral positions, and eventually got the job here at the Smithsonian which has just been perfect.
It combines the public education through the exhibits, which I really enjoy, and it allows me to go on any field expeditions I want to any time of the year, because I’m not tied to a teaching schedule. And there are some really wonderful resources, here, in terms of people and collections, that its just fantastic to be a part of it.
So I have to juggle all these projects, that’s one of the prices of being interdisciplinary, but I keep my hand on the geology and fossil beds, because that’s where I really want to apply what I’ve learned from the modern ecosystem. But I also keep going back to the modern one, and there’s this constant interchange of questions and answers between the modern analog study and the research on the fossil deposits. In a way that’s pretty much what I hoped for.
More thoughts on fossils and bones
Fossilization doesn’t take a long time — and the chance of making it into the record are better the quicker it occurs.
Dr. Behrensmeyer: We don’t dig them up, but we can still see the little parts that are still poking out of the ground. It’s all been a great lesson in how fast things can disintegrate, but also the value of quick burial. And we’ve tracked the mineralization that’s occurring there. We’ve actually collected bones each time that we go back and the bones are in the laboratory here. I’ve had a geochemist working on the minerals that are forming in the bones, in periods of as little as 12 years. So fossilization doesn’t have to be a slow process.
But basically the lesson I’ve learned, if you’re not buried and beginning to mineralize after a few tens of years, your chances of surviving into the long term fossil record are pretty slim, at least if you’re a vertebrate.
There are lots of fossils out there!
Some fossils are striking: whole bodies are preserved with the hair and stomach contents. Mostly the remains are pretty fragmentary. But there are many of them! The deep sea floor is covered with fossils of very tiny organisms that are complete.
Fossils are actually relatively common if you know where to look. Tyrannosaur fossils are not common, but the teeth of rodents that lived in the ice ages are actually pretty common. It depends on the type of organism and whether you want a museum quality specimen or something for research. There’s plenty for the research paleontologist!
The teamwork is what I’m trying to convince them is one of the most exciting things about being a scientist and being a paleoecologist. You have to work with other people, you have to work with a lot of other ideas, and be careful not to step on toes, and give other folks their due, and that’s the kind of thing you also have to teach your children.
When I was a child I remember my mother and father would always talk about people who sparked them, who created sparks in their minds. … You can think better when you have other people around and are trading ideas. For me, I just love getting together over the campfire or around the dinner table in the field … and you trade ideas, or just walking out to outcrops during the day, and its morning and the birds are singing and its beautiful and everybody’s fresh and you start talking about “maybe I’ll go over here and test this hypothesis today”, and do you want to come along? And maybe you can tell me something I don’t know about the sediments or the rocks … It’s a great way to spend the day.