SciCafe: Secrets of the Crocodile Mummies

SciCafe: Secrets of the Crocodile Mummies - Transcript

Evon Hekkala (Research Associate, Division of Vertebrate Zoology, American Museum of Natural History):

So, this is SciCafe, so before I get started I want to actually talk a little bit about science versus just talking about crocodiles.

So, one of the things that I think is really important is science communication and sharing with people how people get involved in science. Because I think that a lot of people feel like they can't participate in science these days. A lot of people feel like there are scientists and nonscientists. And so - I'll get to the crocodiles, I promise, but one of the things that I really want to express is that for me I had a really unorthodox beginning to my career. So, I'm going to talk a little bit about that first.

So, first of all, what are scientists? So, a lot of you probably like to dance, but you might not get paid to dance, but that doesn't mean you can't participate in dancing. And a lot of you can probably drive and you don't get paid to drive, but that doesn't mean you can't participate in driving. And so I have the perspective that there are some people who get paid to do science, and there are a lot of people who can participate in science without getting paid for it. And I think that we're all born with the ability to do science. The very first experiment anyone ever does is dump their Cheerios or their milk or whatever on the floor and test gravity. So, we all start out with it. And where does it go? What happens? Why do people stop questioning the world around them?

And I think one of the things that happen is a lot of people get told, "Well, it's just the way it is," or "because I said so," or "don't ask questions, I'm busy." And I think it drives that inquiry-based thinking out of a lot of people's lives, and then they start feeling like that's something other people do. And the one thing that I had that a lot of people don't have is I had a mom who never once did that to me in my entire life. So, this is fossil Oregon. This is population 200. It's in the middle of Northeastern Oregon, and it's in the middle - it turns out it's in the middle of the John Day Fossil Beds, which is how it got its name. And those are actually kids taking their sheep to go get an ice cream at the mercantile. And this is not an old photo. This is like now. [Laugher].

So, this is - I was born right outside of this town. And what's really cool is I had no idea at the time that I would end up working in an institution that actually houses some of the most incredible fossils from the John Day Fossil Beds in the world. So, one day I was looking in a drawer and it said John Day Fossil Beds. I'm like how did that happen? It wasn't fate. Mom sent off my portfolio when I was in high school to art school because she wanted to get me out of the town that I was in. And I got into art school because I guess I was a decent artist. And I hated it, but I loved art history, which is great. So, I decided to stick with art history. This is all going to come in later.

And while I was doing my art history undergraduate degree, I took a course called The History of Evolutionary Theory. And that course changed my life partly because of the topic and partly because of the woman who taught it. And I'll never forget her name. Her name was Mildred Dickemann. An amazing teacher. And she was this very challenging person, and she helped me explore and understand how to figure out the relationships among living things on planet Earth. And one of the things that I was really interested in was the relationships of humans to their relatives. And I wanted to understand why certain organisms have conflicts and other organisms don't. And so I thought if we could understand the history of the social behavior of primates, that might help us understand why people fight with each other. Because I just want - maybe if we can understand it we could stop it. I don't know. I was young, naive.

And so the very first thing I decided I wanted to do was get DNA from Neanderthals. And everyone said that's never going to happen. And then the next thing I did was I said, well, maybe if I studied primitive primates I will be able to understand how social behavior evolved. And so lemurs in Madagascar - you've all heard of lemurs, I'm sure. They have these female-dominated social systems, for the most part. And they resolve conflicts, in some cases, by having stink fights with their little glands on their wrists. And they have all kinds of little interesting social behaviors, but they're really matrilineal dominated social groups. And I was like, "well, this might be the key. I'm going to go to Madagascar and study why lemurs have females in charge, and maybe they have something that we can learn from them about social conflict."

So, I went to McGill University on an exchange program in Canada, and there's this crazy other story of how I did that. It was basically because I was mad at a boyfriend. I didn't even know where Canada was or McGill or Montreal or anything. [Laughter]. But I ended up working at the Red Path Museum in Montreal for a while where I fell in love with museums. So I decided to go to graduate school at Columbia University to go off to Madagascar to study red-ruffed lemurs. We all know where Madagascar is, I hope at this point. There's this big giant continent over here, and then there's this island over here: Madagascar. And I went to Madagascar and did this epic trek across northern Madagascar only to discover that everywhere I went people had eaten the lemur populations that wanted to study. And so I had no dissertation project. And I honestly can't blame the people in northern Madagascar. These are entire families living on a bowl of rice a day. So, that's a whole other conservation story, and we can talk about that as well, but I came back with no project.

And luckily I had graduate advisors here at the Natural History Museum. He basically gave me the choice of two bags: bag number one, bag number two. There's this cute thing over there. I'm not much of a cat person. Can anyone guess what I choose? [Laughter]. Crocodiles. And the reason I choose crocodiles is actually because when I was in Madagascar studying the lemurs I had actually noticed that there were really interesting human social norms surrounding crocodiles. And one of those was that people worshipped crocodiles in a lot of places. And another was that people had been feeding crocodiles in certain lakes for like 1,000 years. Some people thought the crocodiles were their ancestors. So, crocodiles were really sacred there. And they lived in volcanic cores. They lived in some really interesting places. They live in caves where they just eat shrimp. And I had heard that they were actually just originally described as a separate species: crocodylus madagascariensis. And nobody in this room needs to realize what all this means other than to say these are all the different things that just the Nile crocodile has been named throughout its history. But crocodylus madagascariensis is one of those thing. So, I was like I'm going to go to Madagascar and I'm going to figure out whether or not these are actually a separate species.

Most people don't realize that by the 1970s all the crocodilians - that includes not just the true crocodiles, not the alligators, there's all these other species in this group were on the verge of extinction. We had wiped almost all of them out. We had used them for boots and luggage. We had persecuted them because they were a threat to livestock and in some cases people. People were scared of them. They just wanted them gone. We had converted lots of areas from wetlands into housing. And so crocodiles were one of the first case studies of sustainable use of a wildlife product in order to bring it back.

So, what they did was they had communities that had crocodiles around them, get into agreements where they would harvest some of the crocodile eggs and they would raise those hatchlings up and they would sell the products either as meat or as leather in order to make it worthwhile for people to live near this animal that was potentially a dangerous threatening animal to them or their livestock. And the reason this could actually work is that crocodilians, for the most part, they'll have really large numbers of eggs in their clutches, so anywhere from 40 to 60. And usually about 10 percent of the eggs actually hatch, and maybe one percent makes it to adulthood. So, the natural offtake from populations is pretty extreme. And so they thought this would be a good way to bring crocodiles back and have some sort of benefit for the communities. And the tricky part about this - well, I should go back for a second - is fads happen. So, what if the market falls out of crocodile products? What if nobody wants to buy crocodile products anymore?That can be a problem. They wouldn't be worth anything. All these communities would have all these crocodiles. So, then they might decide they're going to harvest all the crocodiles right away to try and get some money, or something like that. So, there are some potential disincentives in there.

But the other big issue is monitoring crocodile trade because crocodiles are one of these groups that it's almost impossible to tell crocodiles apart unless you're a specialist. Most people have trouble telling an alligator from a crocodile. That's the number one question I get. And some of you might actually wonder. Alligators and crocodiles are really not very - well, they're closely related, but they're very distantly closely related. So, way in the past they split off about 60 million years ago. I don't study alligators at all. I only study crocodiles. And crocodiles are babies relative to alligators. Alligators are really, really old. But, anyway, it's really hard to tell them apart. And there are very few people - maybe 30 people in the world that could look at a crocodile and tell what species it is just at a glance. And certainly, when they're products like skins and things they're really hard to tell apart.

And so I wanted to develop a genetic monitoring system, so we could see if we could monitor the trade and see where products were coming from because that would make this whole process more sustainable. You don't do science in a vacuum, so I was thinking how on earth am I going to do this project. So, I reached out to a lot of people because there was certainly no way that I could travel around the globe collecting samples of crocodiles to understand crocodiles' genetic relationships. So, I enlisted a lot of people to send me samples, but the other thing is, because I had worked in museum collections, I knew that there were all these specimens in collections. And so this right here is an egg from this institution, the American Museum of Natural History, that was collected in 1930. And you can see the label. It actually says crocodylus madagascariensis. So, I knew that there were all these treasures stored in these institutions that could be used to answer this question. So, I didn't necessarily have to go travel the world to get the samples.

But the other thing - because of my bizarre background - was that I also knew that there were crocodile specimens in anthropological collections and art history collections. I knew that there were crocodile mummies. And so when I needed to fill in gaps in my study, I was like, well, maybe I could get DNA from crocodile mummies. Nobody told me I couldn't. At that point, I had never met somebody who said, "Oh, there's no way that's ever going to happen."

This is a crocodile hatchling that was mummified by the ancient Egyptians about 2,000 years ago. I was able to take little, tiny samples from the tails of crocodiles that were mummified and actually get really good DNA from them. So, when you work on this stuff you have to work in what's called an ancient DNA room. And this was before Next Generation Sequencing, which I'm going to talk about in just a minute. You have to be really clean and really careful.

And we just sort of were really lucky. I was able to get DNA. These are little bands of DNA; just a pretty picture I like to share with everybody. This is the old way of getting DNA. Now, we do it in a different way.

So, what did we find? This crazy surprise. All of a sudden, we had data - genetic data that actually showed that the Nile crocodiles were two completely separate groups. So, on the left you have white dots and on the right you have red dots. Those were genetically completely different. And I was like what's going on? I must have screwed up. I'm an art history major. I don't know what I'm doing. So, I redid everything a lot of times. And working with other collaborators we were able to extend our study to include all the species of crocodiles, not just the Nile crocodiles.

This is a picture of most of the true crocodiles - the living, true crocodiles, genus crocodylus. And at the top you have the New World crocodiles. There are four species in the Caribbean. We had what we thought was one species in Africa, and then we have all these Asian species: the Siamese crocodile, the Mugger crocodile, the Salt Water crocodile, all these other species. And you see right there there's this little red box that says crocodile niloticus five and six. Those were from Western Africa, and they were not as closely related to the other Nile crocodiles as were the ones from the Caribbean. And when we see this in science, it means that they can't be the same species. There's no way they could be the same species. So, we published this paper.

The other cool thing was that the relationship between the Nile crocodiles and the Caribbean crocodiles; the New World crocodiles, we dated the timing of that divergence between those species. And it was really, really recent. So, it had to have taken place when the Atlantic Ocean was in its current position, so three to six million years ago, which meant that they had crossed the Atlantic Ocean. And it seemed crazy at the time, but then we realized the natural history of crocodilians is such that they can store sperm. They can not eat for 10 months. And actually, these routes across the Atlantic were ones where people used to ride those trade winds to get from Africa to North America. So, it wasn't that farfetched to think that. But you're wondering about the mummies, I'm sure.

Don't be scared - is just a diagram showing branching relationships of all the samples. And what we have on the right is all the Eastern samples: the Nile Nile crocodile. And on the left, we have all these Western samples of this thing that was completely different. And the light gray patches in it were all crocodile mummies. And so all of the mummies fit into that light gray patch; the Western group. So, we knew whatever those mummies were was this other species.

The other really interesting thing we found out was that if you looked at just the modern samples - the ones on the left - you had this big split.

But if you looked in the museum collections up to 1922, they actually both co-occurred in the Nile, which meant that we're actually losing the Western one. Really recently it had been previously more broadly distributed.

So, what do you do when you find a new species? A lot of people have no idea how this works. It's always in the movies people name things after themselves. This is bad. You would never ever, ever do that. That's really tacky. [Laughter]. What you do is you do due diligence. You do all the research to see, well, who named this before? Is there any chance anyone did? Did anyone ever describe it way back in history? So, now you're going to ask me what did Napoleon have to do with this.

Napoleon decided to go on an expedition to Egypt, as some of you know, because we have an obelisk in the park. He took with him a whole bunch of scientists. And the reason he wanted to take scientists with him was because he wanted to find out what the resources there were. He also just wanted stuff. So, this guy Geoffroy Saint-Hilaire was an anatomist at the Paris Museum of Natural History, and he went on this expedition with Napoleon. And he was really interested - I love this story. This guy's one of my heroes. He thought if he looked at mummies he would be able to see change over time in populations of animals. So, he actually believed if you looked at a mummy, you could actually see a difference over a couple thousand years. And this is near and dear to my heart, as you will see soon enough.

But so he had gone and collected all these mummies in Africa, in Egypt. When Geoffroy Saint-Hilaire got back to the Paris Museum of Natural History, he started going through all this material of the mummies. And he found this little mummy skull, and this is a picture of the actual skull with India ink writing on it from the expedition from 1807. And Geoffroy Saint-Hilaire thought this looked different. He described this as a separate species, crocodylus suchus. And the reason he chose that name - it was for the sacred crocodile, the god Sobek that the ancient Egyptians recognized. And he actually used the even more ancient literature Herodotus and other things, and used anecdotal evidence to describe this species based on behavioral things. It was considered more tame. It was small. It was kept in temples. And the Egyptians actually recognized this as different from the Nile crocodiles. And this is the paper he wrote: The Two Crocodiles Existing in the Nile. And he describes this thing as Crocodylus suchus in here based on this mummy. And there's even earlier little notes that talk about this tiny other crocodile in the Nile. So, we went with Geoffroy Saint-Hilaire's description, and we just re-described this as Crocodylus suchus.

So, we rediscovered it, and we published this a few years ago. So, crocodylus suchus, that's the tiny skull that had actually been missing. They found it while I was doing this research. And the really cool thing is that now we're working with people who have mummy collections and we're trying to find out if we can confirm whether or not all of the individuals that they mummified were actually this one species and not the other.

So, people from the Brooklyn Museum were here recently with some of their mummies, and we were using the CT scanner here. And one of the things we think we can do now is we can go back into the collections and use - now that we've used the DNA to re-identify all these individuals, we can go back and do all these measurements of their skulls to be able to try to figure out if we can characterize them based on their skull shape. You can actually see the India ink writing that was on the sticks because it had some sort of metallic compound in it.

All right, the other really cool thing about this is that the Nile crocodiles that are here in the museum in the dioramas, these are the original archival photos that they took for the upper Nile group that's in the Akeley Hall. And this is that diorama. And if you see in the back right there - we'll do a little popup - the guy in the back is a painting. This guy in the front is actually a taxidermy crocodile. And so we have DNA from these and we show that this is actually the species that we re-described. And this brings me to my other great passion, which is the dioramas here. I'm going to get back to the crocodiles - don't worry. So, I have this project I keep trying to find a home for. It's called DNA from Dioramas. Because if you don't know - I'll tell you- all of the dioramas in the Akeley Hall of African Mammals are real places. They actually really existed and they may still exist, depending on the conditions there. But all of the individual animals in those dioramas, their skeletons are in the collections here. So, this institution holds thousands and thousands and thousands of museum specimens. And so we can use the DNA from - we don't have to go into the diorama and mess with the art in the diorama. We can go into the collections and get DNA and see what's changed over the last 100 years since these were done, and look at global change and wildlife populations over time. And we're actually doing this with leopards, and it's working really well. It's exciting. So, get back to the crocodiles, sorry.

So, this whole project got me thinking about why some animals are sacred. Why are some animals sacred? Is it because people just really like them? Well, I noticed when I was studying crocodiles that crocodiles have this incredible ability to heal themselves. So, you find these crocodiles that have these horrible wounds, these giant missing limbs, gaping wounds, bites. They're in these cesspools of nasty gook, and they're fine. And it's like how do they do that? What is the magic ability to resist these pathogens in the environment? Well, I wasn't the only one who thought that.

So, if you go back and look at all these medieval curiosity cabinets and things - and because I was an art student, I looked at these paintings a lot when I was working on my crocodile project - you see all these pictures with crocodiles on the ceilings. We're going to play this game called spot the crocodile. [Laugher]. Oh, spot the crocodile. That one looks a little bit like an iguana. Spot the crocodile. Oh, there's another one.

So, what's going on with this? People believed that crocodiles had some ability to heal. They had some healing property. They didn't know what it was necessarily. But now people are starting to research it. So, a few years ago some people in Asia started to look at what's going on in the blood plasma of Siamese crocodiles. And if some of you have been here in the exhibit - the crocs exhibit - they actually have some Siamese crocodiles here at the museum right now during the croc exhibit. And Siamese crocodiles are critically endangered. They're on the verge of extinction. And this was the species that they first found that they have this incredible - their blood plasma has unbelievable antimicrobial properties. So, they tested it against all kinds of staphylococcus and strep and all these other infections, and they found that in at least an experimental design it was almost as effective as any modern antibiotic.

Now, what I don't want anyone to do is go out and start draining the blood from crocodiles to fight their infections. But what we do know now is that we almost lost - in the 1970s - this incredible reservoir of genomic knowledge of how to fight infections. But now we can do studies on it. We can research what is it in the genome of crocodilians, crocodiles, that actually allows them to have this incredible resistance to pathogens. And a couple years ago, people sequenced the genomes of three crocodilians: the alligator, the Salt Water crocodile and the gharial, which is one of the long, slender snouted crocodiles. And they were able to find that the immune system in crocodilians is in triplicate. So, they're major histocompatibility complex is in triplicate. It's a really, really interesting difference from other organisms.

Let's get back to Madagascar just for a minute. So, the other thing that I discovered when I was going through the collections in museums is that there's this mysterious crocodile in Madagascar besides the Nile crocodile. It's called - it was originally called crocodylus robustus, and the Malagasy horned crocodile. This is a skull. It's on display here at the museum. And there are about 13 specimens here at the museum. And the really weird thing about this thing is it was alive and well in Madagascar until humans got there about 2,000 years ago. And also Nile crocodiles got there about 2,000 years ago. So, this is a great forensic story. It's a forensic mystery. So, what happened to these? Did they die out on their own mysteriously at the same time that people and Nile crocodiles got to Madagascar? What happened?

In the collections we also have some really interesting clues. So, this is a picture of one of the skulls here in the paleontology department, and it has this hole - you can see where the string is - that may be a wound from something like a spear. It doesn't fit a crocodile tooth, we know that. So, that's a curious thing about it. The other question is whether or not the Nile crocodiles and this thing coexisted at the same time. So, there's this very early report - this guy Humboldt, he traveled to the center of Madagascar and found these crocodiles, and he brought back bones to the people who described this extinct crocodile. And they said, "Oh, yeah, this is the extinct crocodile." He said, "Yeah, well, but it's still living there." And so now what we want to do is use DNA to actually tell what this thing actually was. Was it a true crocodile? Because if it was a true crocodile, genus crocodylus, then it's possible that it could have hybridized with the Nile crocodile and could have been lost through genetic swamping or maybe the ghost of its DNA is still there. We don't exactly know.

And so we just - after three years of trying - got data DNA from this thing. We used this new approach. It's called sequence capture where you use little bits of DNA as fishing lures to pull DNA sequences out of extinct specimens. They've used this on mammoths. They've used this on ancient horses, and they've used it on Neanderthals. It kind of irks me because, that was my idea years ago before we were able to actually amplify DNA. [Laughter]. Anyway, so we just got the data, and I'm not allowed to tell you about it because it's really exciting. So, stay tuned. We'll keep you posted. We're just - our preliminary data are really interesting. It's a little too soon to share with you what this thing is, but it's really, really exciting. And it's another one of those things like the mysteries in the drawers in this museum are never ending. It's really, really exciting stuff.

So, I don't have a lot else to say expect for one thing I do want to point out is I said earlier I didn't choose the cats. I chose the crocodiles. I'm not a big cat person, but I'm always an underdog person. And so that's Rosalind Franklin, who was the co-discoverer of DNA. That's Geoffroy Saint-Hilaire and this is actually Raymond Dart, who discovered Australopithecus, and no one believed him either. So, don't let people tell you it can't be done, don't do it, it's not worth trying. And a lot of the best science that was ever done in the history of humanity was done by farmers and gardeners and people who were not labeled scientists.

And, with that, I will let you guys ask questions. [Applause]. Thank you.

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