How Do We Know What Extinct Animals Ate?

Transcript

ERIC: From the Museum of Science in Boston, this is Pulsar, a podcast where we sink our teeth into the best questions we've ever gotten from our visitors. I'm your host, Eric, and we love questions about extinct animals. Sometimes questions we get are about when and why certain kinds of life disappeared, like the 50-foot-long shark, megalodon. But other times, visitors want to know what ancient animals were like in life. Since the only evidence we have of, say, Tyrannosaurus rex is fossilized bones, we have to squeeze every clue we can from them to paint a picture of how T rex moved, what it looked like, and what it ate. But it turns out that science is getting better every year at finding more clues and adding to our knowledge of, among other things, the diet of extinct animals. Joining me today to discuss how we know about the eating habits of animals that haven't existed on the earth in millions of years is Morgan from our programs team. Morgan, thanks for joining me on Pulsar.

MORGAN: Awesome, I'm so happy to be here. This is so cool.

ERIC: Okay, so let's start big picture. We can divide animals into a few big categories: carnivores that eat meat, herbivores that eat plants, omnivores that eat both. What are the first clues we look for an ancient animal to put them in one of these categories?

MORGAN: Sure. So if we happen to find a really nice fossil out in the field, we'll probably figure out what category they go into by comparing them to a modern carnivore, herbivore, or omnivore. So we can look at the shape of the tooth to figure that out. So if we think about carnivores, today, they have really sharp, sharp teeth, they're really pointy, because they have to be able to tear food apart, kind of like when we're cutting into meat with a knife. They have to be able to cut food apart with those sharp teeth. On the other hand, herbivores, well, they tend to have really wide and flat teeth, because they have to grind the food down. A lot of the grasses and the plants that they're eating, they have to make sure that it's into smaller bits, so they can more easily digest it. And then omnivores kind of like us humans, well, we have a mix of both. We have some teeth that come to a point at the end, kind of like our front teeth, if you feel them, they're kind of sharp at the tip. And then we have some teeth that are really flat like our back molars that are really good for chewing and breaking down food. So we can kind of carry that over in case we find a fossil tooth to figure out what kind of food that animal might have eaten.

ERIC: So cool. So we can look to teeth that we see now, in animals like crocodiles, which are definitely carnivores, that have pointy teeth. And then animals that have teeth like that in the past, we can kind of infer what they ate without actually seeing it eat anything.

MORGAN: Yeah, for sure. Comparison. And inference is so important when we're trying to think about animals from a really long time ago. It's not like they wrote down what they ate.

ERIC: Right, exactly. So that's basically the answer that I would give people when they asked me at the museum, and then you know so much more about what we can find out. Basically, science is much better at figuring out what an animal ate in the past than just that first big picture. Carnivore, herbivore, did it eat plants or not? So what else? Can you tell what is the next step in figuring out what kind of food and animal ate? Can you tell anything else about the teeth?

MORGAN: Yeah, for sure, we can get a lot more specific, especially when we're talking about herbivores and thinking about what kind of plants they ate. For example, there are two categories of herbivores. Browsers, which are animals that eat bushy leaves. So think about like leaves and twigs and stuff from trees. And there are grazers, so herbivores that eat mostly grasses. And believe it or not, the teeth on those animals are quite different if we look at them close enough. So one technique that some scientists use is called microwear. And in this technique, we zoom in super close on the tooth using a microscope, and we'll look for microscopic dents or scratches on the tooth. So if there's a lot of dents on the molars, or if there's pits, that may tell us that this animal ate a lot of really hard food, this animal might have eaten things like twigs or nuts, something really hard that might be grinding into their teeth. On the other hand, if there's scratches, and a lot of vertical and horizontal lines, that probably tells us that the animal was sharing on blades of grass and stuff like that. So that's one way that we can kind of differentiate between different kinds of herbivores, which is actually really helpful.

ERIC: It's amazing that when you think about the fossils of the teeth, they're not the teeth themselves. They're the imprint that the teeth leaves behind. The teeth and all the bones get replaced by rock over millions of years. So the fact that this rock has those same scratches and dents on a microscopic level, I didn't even know that that was possible to get that much detail out of looking at a tooth that might be 100 million years old, and it still has a tiny dent from that animal eating a twig. It's amazing.

MORGAN: Yeah, it's really, really awesome. And something even more cool is that the dents and twigs, when we're using the microwear technique, it tells us very specifically the time in the animal's life that it ate those. So if we're looking at the dents and scratches, that tells us about the last meals that that animal ate before it died, and it gives us a picture of that animal on one of its last days.

ERIC: Now something else that people don't really think about. Many animals have gone extinct. Famously, the dinosaurs, many of them aren't around anymore. But plants go extinct, too. And if we looked around in a forest at the time of the dinosaurs, we would not recognize a lot of it. So do you have to study the ancient plants and fossils of those to know what kind of imprints they might have made on the teeth?

MORGAN: Yeah, so there's a whole section of paleontology that's thinking about plants and pollen. So yeah, we definitely have to get that kind of evidence. And it kind of goes both ways, right? If we find that an animal or a dinosaur was eating a certain kind of plant, then that tells us that during that time period that grasses or trees were around in that animal's habitat. Similarly, if we find a plant from a certain number of years ago, then that tells us that they were probably animals that were eating that kind of plant. So both of these fields and focus topics kind of blend into each other.

ERIC: So there's more that we can learn as well. So what kind of other analysis can you do on the fossils to find out more about the type of plants that it ate? Anything else you can do?

MORGAN: Yeah, so my favorite technique, the thing that I think I probably know the most about when I'm thinking about the diet of animals from a long time ago, is called isotope analysis. And now sometimes when people say isotope, it can be a little bit intimidating. People are like, Oh, my gosh, isotopes, I remember learning those in high school. But to put it pretty simply, isotopes are just slightly different forms of the same element. And the difference between these two forms of the same element is that they are different masses. So for example, if we're thinking about the element carbon, there's two naturally occurring isotopes, and one isotope has an extra neutron. So one isotope is slightly slightly heavier than the other isotope. Now, we can look into fossils, specifically in teeth, in the enamel, to figure out how much of the heavy isotope there is compared to the light isotope. And this can give us information about if this animal was eating grassy foods or bushy foods. And that's just an example for carbon, we can also look at other elements too. So for example, we can look at elements like nitrogen, or we can look at calcium or sulfur. And this gives us information about all different kinds of things. So we can learn about the source of water that the animal might have been drinking from. So if it was from a body of water, like a lake or a pond, or if it was from like, a year with a lot of rainfall, we can learn about if the animal might have been eating meat by looking at the isotopes of elements such as strontium, or like nitrogen sometimes. And there's a lot of research in this field that's currently ongoing. So this is a lot that we're currently like learning about what isotopes can tell us different things about what kind of foods animals ate. So I love talking about isotopes.

ERIC: Really amazing. It's another set of clues, another layer that's there in the fossils. That's all the evidence that we have. But we can learn so much from it, there's so much to understand, if we just look at the microscopic indentations and the chemical composition. Looking at it from every single other branch of science tells us so much about these animals, even what kind of water they were drinking. It's unbelievable.

MORGAN: Yeah, that can give us clues into the climate too maybe, like with the water, was there years with really, really low rainfall or maybe like a long period where there was a lot of rainfall or maybe, you know, from how many million years ago to how many million years ago, there was a really big body of water that a lot of animals were drinking from. So it can give us so much information not just about the animal but sometimes about the climate too, which is super, super important to understand.

ERIC: And it's so cool that we can tell all this just from mostly the fossil teeth because for some animals, we only have teeth. The giant shark that we've talked to before, megalodon, we don't have any other part of its fossil because because sharks are mostly cartilage instead of bone, but their teeth are fossils the size of your hand, but just in those teeth, we can find out the same kind of information. It's really fascinating.

MORGAN: Yeah, yeah, for sure.

ERIC: So we've talked a lot about the fossils and the animals teeth. Sometimes we get asked about other specific fossils have been found, something like a fossil that's been found with another fossil inside of it that was its last meal. We've also been asked about fossil poop. So can we use these things to to kind of figure out what the diet of an animal was?

MORGAN: Yeah, if we're lucky enough to find them. They're not as common as teeth. But if we can find them that can be super informative to. So if we're able to find the fossil inside of another animal's gut, well, yeah, that definitely tells us the last meal of the animal, we're seeing what's inside of the stomach. So that gives us a really, really direct clue of what specifically they were eating, which is super helpful for carnivores, and omnivores, eating meat. Now, with fossil poop, that can be a little bit more difficult. It's still informative. But if we find the poop, and not the animal around it, we can't always make a direct connection between what animal left that poop, but it's still always, always fun to find any fossil in any form.

ERIC: So dinosaurs are just the most famous of any group of extinct animals. But there's a lot more out there. Do you really love to teach about dinosaurs? Is there another group of animals that you like better?

MORGAN: I actually don't know that much about dinosaurs, believe it or not. I like thinking about animals from the Cenezoic. That's my favorite time period.

ERIC: Ooh, so that is after the dinosaurs?

MORGAN: Yes, so it's the age of the mammals when the mammals got really, really big.

ERIC: Okay, so what kind of cool mammals were there? And what did they eat?

MORGAN: Oh my goodness, let me tell you about theropithecus. It's a type of monkey. So if we think about the modern gelada. There were past theropithecus monkeys that were absolutely huge. And we can look at isotope analysis to find out if they were eating grasses, or if they were eating bushy leaves and stuff. And from studies, we found out that a lot of them were eating grasses, or a mixed diet, which is really cool, because it was kind of indicating a transition in the diet of certain monkeys.

ERIC: Cool. So you can not just get a snapshot of what an animal was eating at a certain time. But you can even see transitions as animals evolved. And as the Earth changed, and its climate and what plants were around, you can kind of get that dynamic picture of how things were changing even.

MORGAN: Yeah, for sure.

ERIC: And so to wrap up, I always like to think about the future. And for this subject, it makes me think of what else is out there. I mean, when we hear about fossils being found, that's just one animal out of all the animals of that species that ever existed, maybe millions are more so thinking that there's always a more complete fossil out there, or a fossil from a different time than we found before might tell us more. It's just exciting that there's that, and the technology always getting better, too. I mean, is there anything else coming up or technology getting better that you think we might be able to find out even more?

MORGAN: What I pay a lot of attention to our new isotope studies. If we can find really strong links between, you know, a certain element and that correlating with an animal's diet that I think is a frontier that a lot of people are looking into right now.

ERIC: All right, Morgan, thanks so much for telling us all about how we know what extinct animals like to eat.

MORGAN: All right, I'm so happy to get to talk about it.

ERIC: On your next visit to the Museum of Science don't miss our Dinosaurs: Modeling the Mesozoic exhibit, where you can make observations of the teeth of our life-sizes T. rex model, and Cliff, one of the most complete Triceratops fossils in the world. And while you're at home, take a virtual trip to the exhibit to explore the disappearance of the dinosaurs in our Sparks of Science video series. Until next time, keep asking questions.

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