Nicholas Longrich, postdoctoral fellow in the Yale Department of Geology & Geophysics, published an article in the Feb. 29 issue of the journal PLoS ONE, claiming that two similar dinosaurs are actually different species, not just adult and juvenile versions of the same species. A self-proclaimed defender of Cretaceous diversity, Longrich hopes that his research can be a methodological example for other groups hoping to clarify questions of classification. The News spoke with him about his research and plans for the future.
Q What led you to ask this question about the triceratops and the torosaurus?
A Well, it wasn’t much of an issue until recently. There was a paper put out by some researchers from a museum in the Rockies questioning whether they might be the same. And the basic idea is not, on the surface, all that far-fetched in the sense that the argument is that what looks like separate species might in fact be young and adults of the same species. This has happened in the past — the classic example of this is an animal they named nanotyrannus as a kind of dwarf tyrannosaur, and it’s since been shown it’s just a juvenile T-rex. It’s about the same time, same place, it’s clearly not a mature animal, and we can line up all the skulls from smallest to largest and they grade perfectly from a nanotyrannus-type thing into a T-rex. So it’s definitely the case that you can mistake a juvenile for a new species … and it’s been proposed that that’s what’s happening here … but I kind of wanted to push back and say no, we’ve been doing it right. There’s been this back-and-forth between having lots of species or having too few, and it’s not just paleontology, I think it’s taxonomy in general. Nowadays people discover new genes, back then they discovered new species. It was a big thing to describe them, and so they named tons and tons of species and over the past hundred years people have been more conservative and kind of whittled those down. But now it’s kind of swinging the other way, and I think as we’ve gotten a little bit better at classifying things and coming to understand variation more and evolution, we’ve come to realize that there are quite a few species. Maybe not quite as many as the Victorians were naming, but quite a lot. So there’s kind of this perpetual war on how to classify life — there’s naming a species, but first, how many species are there?
Q And without live tissue to distinguish, it must be very difficult.
A It’s difficult, and even with living animals it can be tricky. I think the issue is that people like to think in discrete categories, you know, like you’re either this or you’re this. And nature doesn’t work like that, nature is about continuums … I mean the tree of life, ultimately, all these species, if you go back far enough, they all turn into one species, and so there are no hard and fast lines. You’re trying to draw distinctions between things that are ultimately continua and there are points along those continua where it’s really clearly distinct, but there are other places where it’s a bit iffy.
Q So what kind of metrics do you use to determine that?
A Species, or years, or — ?
Q I guess, in this particular situation, when you were doing your analysis of torosaurus and triceratops, what assays did you use?
A What we did is we kind of sat down and asked, if you want to tell whether things are juvenile or adults, then how do you do that? And we came up with three things. These are three things, they’re testable predictions, that if you are adults and juveniles of the same species then you have three things, and if any one of them isn’t the case then you have to say that they are different species. The first is that they have to actually occur in the same time and the same place. If the juveniles are all 10 million years older than your adults, you’ve got a bit of a problem. Or if your juveniles are all in Asia, your adults are all in North America … If they’re part of a single population they should have basically the same range … and that is sort of the case here, these guys, [triceratops and torosaurus] for the most part they occur in the same rocks, and they have a very similar range in time, so you can’t reject the possibility that they are one species based on that, but there are two other things. One is if the torosaurus is just the adult triceratops, then fairly obviously it has to be an adult, all of them have to be adults, and that’s one of the new things we did and the main thing that we did was we looked at whether the torosaurus were adult or not by looking at skull sutures … Looking at these things we found a number of torosaurus where the skulls aren’t fully fused up, and that implies that they’re not fully grown. So on that basis, if we have torosaurus that aren’t fully mature, if they’re not adult then they can’t be the adult of triceratops. So that was one of the big things, and we also went into the issue of the third thing that we need. If one is just kind of turning into the other, we expect to see a transformation series. If you line up a bunch of fossils you should kind of see them morph into each other. And we argue that you can’t do that with torosaurus and triceratops.
Q So, I guess as a final question, what implications do you think your research has?
A There are these kind of eternal battles over diversity, but where it really matters is, you have to understand diversity to understand changes in diversity. If you want to understand diversification events like adaptive radiations or how climate change might be driving diversity, or if you want to understand extinction events where you lose species, you have to know how many species there are in the first place.
Q Do you think we’re headed for another mass extinction?
A We’re in it. We’ve been in it for 10,000 years or longer, 50,000 to 10,000 years if not longer than that. We’ve been kind of s—ty to the Native Americans, so it kind of feels a bit mean to blame them for wiping out the mammoths … but that’s what happened. Humans come into North America/South America and all the big animals disappear, and it’s a repeated pattern here. I don’t think people really recognize how severe it is; I think there’s a bigger extinction in Africa than people have recognized previously, 30,000 to 40,000 years, modern humans get into Eurasia and species start to go extinct there — things like Irish elk and wooly rhinos. They get into Asia, species start going extinct there, we’re even wiping out other species of hominid out of southeast Asia. If you remember the hobbits from Indonesia, they were one of the species to get wiped out as modern humans move into the area. Then humans get into America 10, 15,000 years ago, all the big animals disappear from North America/South America. And then they start going onto islands, and they hit New Zealand, they hit Madagascar, they hit all the Caribbean islands, they hit the Polynesian islands. Every place people go, species get wiped out, and it’s the large tasty things with low reproductive rates. And then we’ve gone from that to this wave of habitat modification where we are modifying land for agriculture. So yeah, we’re in the middle of a mass extinction.
Q We are the asteroid?
A Yes and no, I mean the asteroid was crazy, like there’s basically no plant eaters that survived the end of the Cretaceous period, and the reason why is because there’s no photosynthesis. Imagine no food for like six months, and that’s probably what happened, and we’re allowing a functional ecosystem to keep going, we’re not shutting down primary productivity, but we’re taking more and more chunks of it. We’re converting large swaths of land over from feeding bison, whatever, mammoths …
Q To feeding us.
A Yeah, wheat for humans, corn for cows. And the remaining species we haven’t hunted to death for their meat are being marginalized … but yeah. Come back in a couple of months and we’ll have a cool new story for you. We have a cool fossil snake that is a transitional snake between lizards and snakes. The body is all snakey but it has the mouth of a lizard.