What crocodile bones teach us about dinosaurs

investing in creative thinkers and problem solvers who help people, communities, and the planet flourish. More information is available at Hewlett.org. You're listening to shortwave. From NPR. Hey, shortwaveers, Regina Barber here, get excited because today we're talking about dinosaurs with science reporter, Ari Daniel. Hey, Ari. Hi, Regina. Okay. I have got a riddle for you. Okay.

“What do you get when a team of researchers walks onto a crocodile farm?”

An academic team building exercise. Perhaps one with teeth. No, actually the answer is a different

way of thinking about the age of a dinosaur. Yeah, I was not going to get that. Yeah, fair enough. It was kind of a trick question. Okay. Since you brought it up, Ari, I do want to know how have researchers traditionally like estimated how old a dinosaur was. It's been a fairly simple process, according to a new C.H. and Sami Turan. She's a paleobiologist at the University of Cape Town in South Africa. She says you just take those fossilized bones and count up the

growth rings. We always thought that these rings are formed annually. Meaning like a tree, you might imagine one ring per year. Exactly. And then you can plot that and you can work out the growth rate of the dinosaur. So for example, how long did it take T-Rex to grow from a hatchling to a fully grown

“adult? And that's what all of us were doing. Me included. Okay. So how long does it take for a T-Rex”

to become an adult, Ari? Well based on this approach, 27 years. Whoa. But to really confirm this ring counting method, you'd need to study live dinosaurs. Which we do not have. They died. Correct.

65 million years ago about. But I have done some reporting on dinosaurs and one of my favorite

facts is that like birds are dinosaur. So can they see birds? Yep, that's on the right track because the next best thing to look at as you're pointing out is their living relatives, like birds. So we're going on our lovely crocodile tour now and cracks. Oh. We've got some big crocodiles in here. See the males head just moved a little bit to the side. Whoa. Okay. So where is this take coming from? Where are you at? We are at Libonaire reptiles and adventures. An outdoor recreation and education

center. Just outside of Cape Town where Quentin Cronier is the head animal handler. So today on the show, how this crocodile park reveals that scientists may have been over-estimating dinosaur ages. I'm Regina Barber and I'm Ari Daniel and you're listening to sure wave. The science podcast from NPR. Support for NPR and the following message come from the William and Flora Hewlett Foundation. Investing in creative thinkers and problem solvers who help people,

communities, and the planet flourish. More information is available at Hewlett.org.

“Okay. Are you here to explain to us like how crocodiles may help us understand dinosaur aging?”

Let's continue our journey into this reptile center in Cape Town. Perfect. So I want you to picture a floatyla of 170 some nile crocodiles lurking in these pools beneath a network of pedestrian bridges. It sounds awful. Well that's where we're at. So scary. They're basically the kings of the water bodies in Africa. I mean they are the custodians of the African rivers. I'll set Mucky manages Libonaire. We respect them and we basically let them be. We give them what they need and we just offer

varying opportunities. And the scientists you introduced us to earlier. A Nusia does she work with the team at the reptile center? Yeah exactly. And I'm accompanying a Nusia as she snaps photos of the beasts below. Really gorgeous. Each of them they have skeletons tell a story about how they grew. So we can say so much about the biology of dinosaurs because we have them as a model to understand dinosaur growth. And even though a zet doesn't study the crocodiles in the same way,

she totally feels that resemblance. It's like walking among dinosaurs if it does. It's um, I'm quite tickled by it on this side. So did the researchers set out with this like dinosaur aging question in mind? Not exactly Gina. A Nusia says that initially she was actually interested in understanding how a crocodiles environment impacts its skeletal growth. Oh, okay. So to study that,

here's what they did. A Nusia and the team at Le Bonier injected several year old crocodiles with

an antibiotic over multiple months. Okay. The antibiotic actually gets taken up in the development

in this bone tissue as like this animal gets older. That's exactly right. Now even before the analysis,

“I spoke with this other biologist who is involved with the study. Her name's Maria Ohenia Pereira”

and she said it was evident that these four crocodiles had unique growth trajectories. They cut together, they grow together, but at the end they have different sizes, different growth trajectory individually. They had different stories. The largest individual of the four grew to more than 80 pounds, which University of Cape Town Technical Officer Andrea Plus got to see up close when she was coming by regularly to measure, weigh, and wrangle the animals. It almost became too

difficult to pick him up on my own. He was definitely a bully and he tried to bully me and he won.

So I had to bring in help. Now Gina, all this happened more than a decade ago. Back when this

place used to raise and kill the crocodiles to sell their leather and meat. Oh, okay. So that's not the case anymore? No, the staff says the animals now live out their natural lifespans. But in 2013, when those four crocs were two years old, LeBonnier got their leather and Anusia got their bones. Mmm. Hey, hey, hey, hey. Thank you. Okay, so we're not at the crox center anymore. I'm guessing. You are correct. This is Anusia's lab, which is at the University

of Cape Town. Okay. She rifles through several slides. Each one containing a super thin cross section of a crocodile arm bone or leg bone. I love the sound of science. It's very calming. Yeah. Maria is the one who prepared these slides and she polished them until the growth rings were beautifully visible. So the time that the light go through the section and you actually can see all the structures is the time that you know that the section is the good one.

Anusia holds one of these slices up to the light. Look at that. You can see some lines looking this area here. Yeah, banding. Yeah. You see that very, very clearly under the microscope, they will be visible. Okay. So what is Anusia and Maria C once they actually did look at it in the microscope? Something unexpected. More rings in some of the bones than they were anticipating. Huh. This is a two year old crocodile and in many cases we found up to five growth marks in the

bones. So there were extra growth marks formed during the short life. Right. You might have thought they were five years old. Exactly. So so what does that mean? Like are they not growing at a

“costume rate? Like are they growing super fast? Like does this mean the counts could be off?”

Perhaps. And this could have some bearing on dinosaur bones because if dino bones were formed similarly, then these crocodile findings suggest that at least some dinosaurs may have been younger when they perish than we previously thought. Right. And similar results in other reptiles as well as kiwi birds back that up as well. Wow. Okay. It changes how we think about how we can use growth marks to determine dinosaur growth patterns. Suggesting Anusia says that

these marks may be better thought of as cycles of growth. This sounds like pretty huge. What do other researchers think about these conclusions? Well I spoke with Holly Woodward. She's a paleo histologist at Oklahoma State University. Studies like this one are really important in adding to that body of knowledge of how often growth rings can be reliable. We haven't really done as much ground truiting as we could with modern animals. But Holly doesn't believe the matter

settled since some modern animals do show annual growth rings and others don't. It's very weird but we can't yet say why or what causes it specifically. But does Holly have any ideas? Well she says it could be due to differences in hormones or maybe day night cycles. But until researchers know more, Holly argues that growth rings remain at least a useful starting point for understanding dinosaur growth. Okay. Okay. So I also talked with Christie Curry Rogers. She's a dinosaur paleo

biologist at McAllister College in St. Paul, Minnesota. It's sort of a cautionary tale not to over interpret what we can see and know based on bone tissue under the microscope. This can form to suspicion that I've often had in my own work because we still don't understand everything we need to about living vertebrates and how their bones respond to the environments around them.

“And what about Anusia, the scientist from Cape Town, like what does she think about all this?”

She agrees that there is more work to be done for sure. We've always estimated the age of a dinosaur

an estimation and even though researchers may not understand the full picture yet,

“Anusia believes that the answers may well be waiting for us. It's all in the bones. It's all in the”

bones. Thanks so much, Ari. My pleasure, Gina. Anytime.

Thanks for listening to our waivers and if you like this episode, please follow us on the

“MPR app or wherever else you may be listening from. And check out some of our other episodes of”

Ari, like the one about scientists scavenging dead whale brains or the one about sludge that could

potentially save the planet, willing to those in our show notes. Reporting for the story was

“supported by a grant from the Pulitzer Center. I'm Regina Barber. Thank you for listening to”

surewave from NPR. So Ari, I do have one more question. Shoot. Do our bones like human bones have rings too? I actually asked Holly Woodward about this and she told me that humans do have growth rings. They are just not reported that often because we usually stop growing in our 20s or so. And the bone tissue that's usually examined comes from skeletons of older individuals. And when we get older, our bones re-model and destroy the presence of previously formed rings.

Wait, so if you were to dig up somebody who died at like 90, the rings wouldn't tell you anything. Or you might not even see rings? Right. Yep. Exactly. Support for NPR and the following message come from the William and Flora Hewlett Foundation, investing in creative thinkers and problem solvers who help people, communities, and the planet flourish. More information is available at Hewlett.org.