What crocodile bones teach us about dinosaurs

Paleontologists have often determined how old a dinosaur was by counting the growth rings in its bones. Just like with trees, it was thought that each ring corresponded to a single year of age. But researchers who studied crocodiles at an outdoor recreation center near Cape Town appear to have poked a hole in that approach. In the crocodiles, which are some of the closest living relatives of dinosaurs, there was more than one growth ring laid down per year. The results contribute to a growing debate over the best way to age animals. Read more of freelance science reporter Ari Daniel’s story here https://www.npr.org/2026/01/17/g-s1-106007/hiv-vaccine-trial-south-africa. Interested in more on the future of science? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:20Regina Barber?

  Hey, Short Wavers. Regina Barber here. Get excited, because today, we're talking about dinosaurs with science reporter Ari Daniel. Hey, Ari.

• 0:28Speaker 02

  Hi, Regina. OK, I have got a riddle for you.

• 0:32Regina Barber?

  OK.

• 0:33Speaker 02

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

• 0:37Regina Barber?

  Hmm, an academic team-building exercise.

• 0:42Speaker 02

  Perhaps, one with teeth. No, actually, the answer is a different way of thinking about the age of a dinosaur.

• 0:49Regina Barber?

  Yeah, I was not going to get that.

• 0:51Speaker 02

  Yeah, fair enough. It was kind of a trick question.

• 0:55Regina Barber?

  OK, since you brought it up, though, Ari, I do want to know, how have researchers traditionally estimated how old a dinosaur was?

• 1:03Speaker 02

  It's been a fairly simple process. According to Anusia Chinsami-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.

• 1:17Speaker 03

  We always thought that these rings are formed annually.

• 1:20Speaker 02

  Meaning, like a tree, you might imagine, one ring per year.

• 1:24Speaker 03

  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.

• 1:39Regina Barber?

  OK, so how long does it take for a T. rex to become an adult, Ari?

• 1:43Speaker 02

  Well, based on this approach, 20-some years.

• 1:46Regina Barber?

  Whoa.

• 1:47Speaker 02

  But to really confirm this ring-counting method, you'd need to study live dinosaurs.

• 1:53Regina Barber?

  Which we do not have. They died 65 million years ago about. But I have done some reporting on dinosaurs, and one of my favorite facts is that, like, birds are dinosaurs. So can they study birds?

• 2:06Speaker 02

  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.

• 2:14Speaker 04

  So we're going on our lovely crocodile tour now.

• 2:17Speaker 02

  And crocs.

• 2:18Regina Barber?

  Oh.

• 2:19Speaker 04

  We've got some big crocodiles in here. See, the male's head just moved a little bit to the side.

• 2:25Regina Barber?

  Whoa, OK, so where is this tape coming from? Where are you at?

• 2:28Speaker 02

  We are at Le Bonheur Reptiles and Adventures, an outdoor recreation and education center just outside of Cape Town, where Quinton Cronier is the head animal handler.

• 2:41Regina Barber?

  So today on the show, how this crocodile park reveals that scientists may have been overestimating dinosaur ages. I'm Regina Barber.

• 2:49Speaker 02

  And I'm Ari Daniel.

• 2:50Regina Barber?

  And you're listening to Short Wave, the science podcast from NPR.

• 3:00Speaker 00

  Stay tuned for the following announcements and messages from our sponsors. This message comes from Capella University. That spark you feel? That's your drive for more. Capella University's FlexPath learning format lets you earn your degree at your pace without putting life on pause. Learn more at capella.edu.

• 3:20Speaker 00

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• 4:16Regina Barber?

  Okay, Ari, you're 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.

• 4:27Speaker 02

  Perfect. So I want you to picture a flotilla of 170-some Nile crocodiles lurking in these pools beneath a network of pedestrian bridges.

• 4:39Regina Barber?

  That sounds awful.

• 4:40Speaker 02

  Well, that's where we're at.

• 4:41Regina Barber?

  So scary.

• 4:42Speaker 06

  They're basically the kings of the water bodies in Africa. I mean, they are the custodians of the African rivers.

• 4:49Speaker 02

  Alzet Mucki manages Le Bonheur.

• 4:51Speaker 06

  We respect them and we basically let them be. We give them what they need and we just offer viewing opportunities.

• 4:59Regina Barber?

  And the scientist you introduced us to earlier, Anousia, does she work with the team at the reptile center?

• 5:04Speaker 02

  Yeah, exactly. And I'm accompanying Anousia as she snaps photos of the beasts below.

• 5:11Speaker 03

  Each of them, their 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.

• 5:26Speaker 02

  And even though Alzet doesn't study the crocodiles in the same way, she totally feels that resemblance.

• 5:32Speaker 06

  It's like walking among dinosaurs every day. So I'm quite tickled by it, I must say.

• 5:38Regina Barber?

  So did the researchers set out with this like dinosaur aging question in mind?

• 5:42Speaker 02

  Not exactly, Gina. Anousia says that initially, she was actually interested in understanding how a crocodile's environment impacts its skeletal growth.

• 5:52Regina Barber?

  Oh, okay.

• 5:53Speaker 02

  So to study that, here's what they did. Anousia and the team at Le Bonheur injected several year-old crocodiles with an antibiotic over multiple months.

• 6:02Regina Barber?

  Okay.

• 6:03Speaker 03

  The antibiotic actually gets taken up in the development of the bone. That leaves a signal in the bone.

• 6:09Regina Barber?

  Okay, so they're like making like a time marker in this bone tissue as like this animal gets older?

• 6:15Speaker 02

  That's exactly right. Now, even before the analysis, I spoke with this other biologist who was involved with the study. Her name's Maria Eugenia Pereira, and she said it was evident that these four crocodiles had unique growth trajectories.

• 6:30Speaker 07

  They hatch together, they grow together, but at the end, they have different sizes, different growth trajectory. Individually, they have different stories.

• 6:41Speaker 02

  The largest individual of the four grew to more than 80 pounds, which University of Cape Town technical officer Andrea Plas got to see up close when she was coming by regularly to measure, weigh, and wrangle the animals.

• 6:56Speaker 08

  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.

• 7:05Speaker 02

  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.

• 7:13Regina Barber?

  Oh, okay, so that's not the case anymore?

• 7:16Speaker 02

  No, the staff says the animals now live out their natural lifespans. But in 2013, when those four crocs were two years old, Le Bonniere got their leather and Anousia got their bones.

• 7:30Regina Barber?

  Hi, hi, Evy. Welcome.

• 7:32Speaker 02

  Thank you.

• 7:35Regina Barber?

  Okay, so we're not at the croc center anymore, I'm guessing.

• 7:38Speaker 02

  You are correct. This is Anousia's lab, which is at the University of Cape Town.

• 7:43Regina Barber?

  Okay.

• 7:43Speaker 02

  She rifles through several slides, each one containing a super thin cross section of a crocodile arm bone or leg bone.

• 7:52Regina Barber?

  I love the sound of science.

• 7:54Speaker 02

  It's very calming.

• 7:56Regina Barber?

  Yeah.

• 7:57Speaker 02

  Maria is the one who prepared these slides, and she polished them until the growth rings were beautifully visible.

• 8:04Speaker 03

  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.

• 8:13Speaker 02

  Anousia holds one of these slices up to the light.

• 8:17Speaker 03

  Look at that, you can see some lines. Look in this area, yeah?

• 8:20Speaker 02

  Yeah, banding.

• 8:21Speaker 03

  Yeah, you see that very, very clearly. Under the microscope, they will be more visible.

• 8:26Regina Barber?

  Okay, so what did Anousia and Maria see once they actually did look at it in the microscope?

• 8:31Speaker 02

  Something unexpected. More rings in some of the bones than they were anticipating.

• 8:37Regina Barber?

  Huh.

• 8:38Speaker 03

  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 their short life.

• 8:48Speaker 02

  Right, you might have thought they were five years old.

• 8:50Speaker 03

  Exactly.

• 8:51Regina Barber?

  So, so what does that mean? Like, are they not growing at a constant rate? Like, are they growing super fast? Like, does this mean the counts could be off?

• 9:00Speaker 02

  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.

• 9:17Regina Barber?

  Right.

• 9:17Speaker 02

  And similar results in other reptiles, as well as kiwi birds, back that up as well.

• 9:23Regina Barber?

  Wow, okay.

• 9:25Speaker 03

  It changes how we think about how we can use growth marks to determine dinosaur growth patterns.

• 9:32Speaker 02

  Suggesting, Anousia says, that these marks may be better thought of as cycles of growth.

• 9:38Regina Barber?

  This sounds like pretty huge. Like, what do other researchers think about these conclusions?

• 9:43Speaker 02

  Well, I spoke with Holly Woodward. She's a paleohistologist at Oklahoma State University.

• 9:49Speaker 09

  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 truthing as we could with modern animals.

• 10:01Speaker 02

  But Holly doesn't believe the matter's settled, since some modern animals do show annual growth rings and others don't.

• 10:08Speaker 09

  It's very weird, but we can't yet say why or what causes it specifically.

• 10:14Regina Barber?

  But does Holly have any ideas?

• 10:16Speaker 02

  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.

• 10:32Regina Barber?

  Okay, okay.

• 10:33Speaker 02

  So I also talked with Kristy Curry Rogers. She's a dinosaur paleobiologist at McAllister College in St. Paul, Minnesota.

• 10:41Speaker 10

  It's sort of a cautionary tale not to overinterpret what we can see and know based on bone tissue under the microscope. This confirmed a 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.

• 11:01Regina Barber?

  And what about Anousia, the scientist from Cape Town? Like, what does she think about all this?

• 11:05Speaker 02

  She agrees that there is more work to be done, for sure.

• 11:09Speaker 03

  We've always estimated the age of a dinosaur. And what this means is that we can still get a rough estimate. But people have to realize that it's an estimation.

• 11:22Speaker 02

  And even though researchers may not understand the full picture yet, Anousia believes that the answers may well be waiting for us.

• 11:30Regina Barber?

  It's all in the bones. It's all in the bones. Thanks so much, Ari.

• 11:36Speaker 02

  My pleasure, Gina. Anytime.

• 11:39Regina Barber?

  Thanks for listening, Short Wavers. And if you liked this episode, please follow us on the NPR app or wherever else you may be listening from. And check out some of our other episodes with Ari, like the one about scientists scavenging dead whale brains or the one about sludge that could potentially save the planet. We'll link 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 Short Wave from NPR.

• 12:09Regina Barber?

  So Ari, I do have one more question.

• 12:11Speaker 02

  Shoot.

• 12:12Regina Barber?

  Do our bones, like human bones, have rings too?

• 12:15Speaker 02

  I actually asked Holly Woodward about this, and she told me that humans do have growth rings. They're 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 remodel and destroy the presence of previously formed rings.

• 12:42Regina Barber?

  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?

• 12:50Speaker 02

  Right. Yep, exactly.

• 12:52Speaker 05

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