What can scientists learn from a single bone?

In 2014 a Field Museum paleontologist found this single small backbone during fieldwork in Zambia. He thought the discovery would end up changing decades of prior research and then he got a phone call. [EXCITING, UPBEAT THEME MUSIC] I'm Brandon Peecook.

I'm a postdoc at the Field Museum. I'm a paleontologist.

EMILY: A couple of years ago you made a pretty significant discovery, that what I was gonna say, sent ripples throughout the paleontology community. – That is way too strong. – I know, that's why I am backtracking – You had a public flip flop in the paleontology circle. – No, how would you say it? – It's surprising implications, yeah.

EMILY: Surprising. B

RANDON: It was, like, a great story of how science kinda happens. Like, you're doing your work as best you can and you think you have one thing on your hands and it turns out you're wrong but for not – not awful reasons and then it kind of changes the whole story of what you were trying to talk about. So I'm part of a research group that's been going to Zambia and Tanzania for over a decade now, we're collecting fossils before and after the biggest mass extinction in Earth history. And so there's lots of cool stuff we find, lots of new species, lots of just awesome straight up specimens, some of the things in the Triassic for instance are, like, the first relatives of dinosaurs. – Wow. – Choice, very good And this one thing we found was in the oldest rocks we have there which are in the Permian period and it was this single vertebra, so a bone from the neck, and, like, right away we're so stoked because we thought it belonged to a reptile, like an early relative of things like dinosaurs and crocodiles way back in the Permian which, if you don't know, is not when we know them from.

They're from much later in time. – So finding this and thinking that it's a reptile. What does that mean? – The global record, all the rocks that are this age all over the world that are preserving, like, land-living ecosystems, we don't find them. It's, like, a huge problem.

Like everybody knows these animals have to exist – Mm-hmm. – But we don't have a record of them. So we have this idea that they would have existed in this period but we've never found them and sometimes those gaps are really, really long for certain groups of animals and that could be due to a whole bunch of different things. And that whole idea is encapsulated by this term called a ghost lineage.

EMILY: All right, hold up. What is a ghost lineage? Well, for example, let's say you're trying to make a catalog of every car ever. You can't just look what's on the road today, you have to go to the junkyard to see all the cars from the past.

Still, one junkyard won't have every car in history, but by identifying which cars are related, for example, made by the same manufacturer, you can make an educated guess that some cars came between the Model T and the Mustang. These missing cars would be referred to as the Mustang's ghost lineage and the gap shortens as additional fossilised cars are found, and can be inserted into the timeline. Ghost lineages exist throughout the fossil record, take the coelacanth.

Coelacanths are ancient, unusual-looking fish that go way back in the fossil record There are coelacanth fossils spanning a massive 300 million years from the Devonian all the way through the Cretaceous. But then no more fossil coelacanths were found and it looked like they went extinct some 65 million years ago. Then, in 1938, off the coast of South Africa, museum curator Marjorie Courtenay-Latimer saw something strange in a fisherman's catch.

Lo and behold, tens of millions of years with no fossil evidence and then here it is. The discovery was mind-boggling. J.

B. L. Smith, the fish expert who conclusively identified the first modern coelacanth, said, "Coelacanth, yes, god!

Although I had come prepared, that first sight hit me like a white-hot blast. "It made me feel shaky and queer,  my body tingled. I stood as if stricken to stone. "Yes, there was not a shadow of doubt: scale by scale, bone by bone, fin by fin. "It was a true coelacanth." The thing is, just because there are no fossil coelacanths doesn't mean they weren't around later than the Cretaceous. It just means they weren't being fossilised.

This 65 million year gap is the ghost lineage of the coelacanth.

EMILY: Okay, tell me about ghost lineages. B

RANDON: So paleontologists always draw, like, things on geologic time where stuff at the bottom is old and stuff at the top is new, like layers of rock. So if we had on this chalkboard time is like this. So you and I are standing way up in the ceiling somewhere today. And so things that are related to mammals have this long thick rectangle here is going to be like a stand-in for their record.

So we have fossils of them going back this far. For reptiles the fossil record for them is a little less but because they have relatives that are also around we can infer relationships, cuz animals, like the mammal relatives, for instance are a certain age older this line representing the relationship between them implies that there should be reptiles here that we've never found before. – Okay. – That's one of the things we're doing in Africa in Zambia is looking for these reptiles and that's what I thought I'd found. – So you thought you had found a reptile fossil that was around here. – Right and so, like, just to put more geology into it, like, if this is supposed to be time going up and down there's a awful mass extinction. The End-Permian Mass Extinction is the worst thing that ever happens in the history of life that we know about.

Immediately after it is when things like dinosaurs and crocodiles and all these other reptiles just explode, so their record goes to that line about. But there should be a record of them in this period beforehand. That's the – that's the thing we're looking for here. – And it hasn't been found yet. – No, there's a few, like this blue rectangle is technically like this.

But not very far down. And so there's, like, almost 50 million years of time where we're missing these reptiles and we should have them. – So Brandon, why is there such a gap? Why would you have such a large period of time with no fossils from that area? – Every ghost lineage that is in the fossil record, you know, might have different answers.

So in this case when we're talking about why we're missing all this time in reptile evolution, it might just have to do with where the rocks are on the planet. So if this doesn't look like Earth to you, it is, just not now. This is about, you know, 250 million years ago, when all the continents are united as Pangea, a vaguely Pac-Man shaped supercontinent with some islands in the middle.

EMILY: Cool. B

RANDON: And so that's Pangea on the surface of the Earth. You know, here's your equator, like that, right? Pangea is about cut in half. And just by happenstance, the rocks that we have that are preserving this time period almost all of them are from like

EMILY: Up there. B

RANDON: And down here.

EMILY: Okay. B

RANDON: Now, if you look at that, paleontologists have always sort of noted what we have for this later Permian period is high latitudes. We don't have a good record of what's going on around the equator. It's really hard to get fossils from, like, land deposits. There's plenty of ocean fossils.

So they're probably just living somewhere in here and we just don't have rocks exposed that are ever gonna give us those fossils, and so for the coelacanth example it's a little bit different because it's going forward in time instead of backward in time. So most paleontology using ghost lineages in this sense to, like, look backwards and predict where there should be animals. – Yeah. – It's very unlikely, very rare cases, where animals are actually alive that we thought were dead. So if you want a fun word, another fun word, coelacanth is actually an example of a Lazarus taxon, – Oh. – One that's gone.

But then, not gone anymore.  – Resurrected. – In terms of scientific knowledge. – Yeah. – So, it's a different kind of ghost lineage. [REWINDING NOISE]

EMILY: And so what do you do with this information? You're jazzed. B

RANDON: I'm jazzed, okay, so we bring it back to the museum, we do museum things. We prepare it, like, we take the rock off the bone, we see the anatomy, the anatomy is even better than we thought at first. It really looks like it's this – I hope – reptile thing and then what's really cool is I did what a scientist would do. I looked at, like, a evolutionary analysis of, like, different features of bones from all these different animals and I kind of plugged mine in to all of these Permian and Triassic reptiles and mammal things and all these different, like, vertebrate taxa, and it totally said, yes, this thing is an early so it's Archosaurs are the group that has crocodiles and birds, it's one of those, and it's in the Permian.

So I was so stoked and so then the next thing you do as a scientist is you tell all the other scientists and they could be like, "nice!" or, "no." And so I made a presentation for the Society of Vertebrate Paleontology meeting and was gonna show everybody my Permian, middle Permian, Archosaur reptile thing and I was jazzed. – You had your poster. – It was printed. It was hung up. I was ready.

And then what happens, is, so, somebody else who I work with, he's the fossil mammal curator here at the Field Museum, Ken Angielczyk, he had done totally different project of this animal that's a mammal relative that's from this – about the same age rocks and we have no idea what its skeleton really looks like and there's one specimen that has a whole backbone and has arms and legs and they CT scan it. – This specimen that they CT scanned... wasn't that one of the specimens that was featured in the the video work that we did with Ken at Harvard? – Yeah, but this is why this is a cool story, right? Because, like, so, when we do fieldwork we're going and collecting whatever we can find. Like, you know, you might be an expert on Triceratops and you're gonna go out and pick up some Triceratops but you're gonna also pick up other stuff. – Mhm. – And so when Ken's doing this bigger work, and I'm involved in this bigger work the ways they cross paths are really fun.

EMILY: Yeah – And that's how science works and that's what's great about a conference is everybody's there talking and you can be like "I don't know!" and you yell for this lady to come over and she's gonna tell you, like, "no, no, no."

EMILY: Yeah – That's what's cool. – Hey, Triceratops lady!  – Triceratops lady! – And she's like, "be there in a minute." – That's right. She's very busy, I'm sure. – Okay, so back to this backbone, and Ken comes up to you and he's like "my pal." – He was so nice about it. So they had done a CT scan, right? So they put this thing into, like, a hospital machine and, like, they can remove all the rock digitally and see what the skeleton looks like of this animal that we've never really seen its skeleton before.

And please remember this is a very obvious mammal relative. 80, 95 percent we find is these things not interesting.

EMILY: Yeah. B

RANDON: He shows me this beautiful digital rendering of a vertebra that is 100% identical to the one I have in Zambia and I only have this one bone. I don't have a whole skeleton. – Yeah. – He's got a whole skeleton. So it's got the head, the mammal head, on the neck and this neck is the neck I have. – Oh no. – So the day of my presentation my poster goes from being like, very exciting, to, like, "guess what you guys, I found another, like, whatever, pigeon in Chicago. "You wanna see?" Like, nobody would care. It's not interesting anymore.

And so, like, on the spot I turned it into, like, a "well, the scientific method is a really interesting uh..." – Way to spin it. – I had to! – Spin, spin, spin. – I had a poster standing in front of for two hours now that's, like, not got... Everything on it's wrong except for the picture of the bone, which is just, that's what the bone looks like. – Yeah, and you have that bone here. – I do have that bone here. It's got a lot of cool features on it, a lot of details.

I hope you can see there's lots of ridges and grooves and holes and weird things going on.

EMILY: Yeah. B

RANDON: And so that – actually it's an isolated bone but paleontologists can do a lot with something like this because that's part of studying this period sort of before dinosaurs is all these animal groups that people know like crocodiles and birds and mammals. They come from animals that are of course alive in the Permian that don't necessarily look like them. So this would like show us the early evolution of those groups. – That's cool. And then you have the digital rendering. – Yeah, yeah.

So this is – so what this is and this is cool too – this is like modern-day paleontology. B

RANDON: So I'm holding this thing that, like, maybe has similar features.

EMILY: That's cool. – That's what is cool! And so this is one of those stories where it's, you know, it's a whole adventure of discovery.

EMILY: Yeah. – The analysis told me this was a reptile thing. – Yeah. – And so everybody was wrong. When of course we weren't wrong, we just had no idea that there were mammals that have a backbone like this and it's just like, ugh! Look, I couldn't get too embarrassed, right? Because it's like, you guys, like, I did my homework. – Yeah. – We're all wrong. – Right.

Science is still progressing. – Yeah, and so what's cool is like, what are the features it actually shares with some reptiles that made me think it was a reptile? And those could be things that have to do with like convergent evolution, like, what do you have to have to have a long neck? Like, what features do you have to have to have a neck to support a head that's on a neck, like, I don't know but that's kind of where we're going now and that started with me finding one bone and thinking I had a reptile and now we're doing things that are totally different.

For paleontology, like in other sciences, major shifts in thinking take place when they are confronted with new information. Brandon's discovery may not have been the leap forward in our understanding of reptile evolution that he initially thought it was, but it was a step forward in our understanding of mammal evolution. When scientific work begins it's impossible to know where it's going to end up.

Remember that series of videos we made at Harvard back in 2015? That research and this episode are funded by the National Science Foundation. The work Katrina and Stephanie were doing at Cambridge allowed for Brandon's discovery to be made even though they were working on completely different projects.

Their CT scans of that mammal ancestor allowed Brandon to realize that his fossil wasn't what he thought it was. Thanks to new and emerging technologies, museum collections, past and present, allowed for these discoveries to be made. With both examples, the rediscovery of the coelacanth and with Brandon's vertebrae, scientific progress often is serendipitous. [EXCITING, UPBEAT THEME MUSIC]

EMILY: It still has brains on it.