What crocodile bones teach us about dinosaurs

Summary

Short Wave Episode Summary

Podcast: Short Wave (NPR)
Episode: What Crocodile Bones Teach Us About Dinosaurs
Date: March 9, 2026
Hosts: Regina Barber & Ari Daniel
Featured Guests:

• Dr. Anusia Chinsami-Turan (Paleobiologist, University of Cape Town)
• Quentin Cronier (Head Animal Handler)
• Andrea Plass (Technical Officer, University of Cape Town)
• Maria Eugenia Perera (Biologist)
• Alzette Monkey (Manager, Le Bonheur Reptiles and Adventures)
• Dr. Holly Woodward (Paleo-histologist, Oklahoma State University)
• Dr. Kristy Curry Rogers (Dinosaur Paleobiologist, Macalester College)

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Episode Overview

This episode explores how studying the bones of modern crocodiles in South Africa is shaking up our understanding of dinosaur aging. Previously, paleontologists estimated how old dinosaurs were when they died by counting growth rings in their fossilized bones, much like rings in a tree. New research using living crocodiles as proxies suggests those age estimates could be off, challenging assumptions about dinosaur growth and lifespan.

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Key Discussion Points & Insights

1. How Scientists Traditionally Estimate Dinosaur Age

• Conventional method:
  • Count growth rings in fossilized dinosaur bones; each ring was believed to correspond to one year (01:03-01:25).
• Dr. Anusia Chinsami-Turan explains:

  "We always thought that these rings are formed annually, meaning, like a tree. You might imagine one ring per year." (01:17)

2. The Fieldwork: Crocodile Relatives as Proxies

• Why crocodiles?
  • Birds and crocodiles are the closest living relatives to dinosaurs (02:07-02:18).
• Research location:
  • Le Bonheur Reptiles and Adventures, just outside Cape Town, houses a large population of Nile crocodiles (03:40-04:05).
• Alzette Monkey (on crocodiles):

  "They're basically the kings of the water bodies in Africa. I mean, they are the custodians of the African rivers." (03:56)

3. Experimental Approach: Marking Bone Growth

• Method:
  • Anusia and her team injected young crocodiles with antibiotics over several months. The antibiotics left a time-stamped marker in the developing bones (05:07-05:23).
• Purpose:
  • This allowed the team to compare the number of visible growth rings to the actual age and growth events of the animals (05:29).

4. Findings: Growth Rings Aren't Annual

• Key discovery:
  • Many young crocodiles had more bone growth rings than their age in years; some two-year-old crocs showed up to five growth marks (07:45-08:02).
  • Notable quote:

    "This is a two year old crocodile. And in many cases, we found up to 5 growth marks in the bones. So there were extra growth marks formed during their short life."
    — Dr. Anusia Chinsami-Turan (07:51)

• Implication:
  • If dinosaur bones grew in a similar fashion, prior age estimates could be inflated; dinosaurs may have been younger than previously thought when they died (08:13-08:31).

5. Expert Reactions and the Scientific Debate

• Dr. Holly Woodward (Oklahoma State):

  "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." (09:03-09:15)

  • Points out that some modern animals do have annual rings, and others do not. The exact mechanisms aren't known yet, and growth rings are still a useful starting tool (09:22-09:46).
• Dr. Kristy Curry Rogers (Macalester College):

  "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 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." (09:54-10:14)

• Dr. Anusia Chinsami-Turan reflects:

  "We can still get a rough estimate. But people have to realize that it's an estimation." (10:22)

6. Memorable Moments & Humorous Asides

• Regina’s reaction to the croc-filled pools:

  "It sounds awful." (03:53)
  "So scary." (03:55)

• Crocodile handling stories:
  • Andrea Plass admits the largest crocodile “was definitely a bully, and he tried to bully me, and he won. So I had to bring in help.” (06:10-06:18)
• Anusia on the bones’ final secrets:

  "It's all in the bones." (10:44)

7. Listener Question: Do Human Bones Have Growth Rings?

• Bonus Q&A:
  • Humans do have growth rings, but they aren’t usually visible in adults because bones remodel with age and erase the old signals (11:29-11:55).
• Brief clarification by Ari Daniel:

  "Humans do have growth rings. They're just not reported that often because we usually stop growing in our 20s or so...our bones remodel and destroy the presence of previously formed rings." (11:29)

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Timestamps for Key Segments

• [00:16-01:47] — Introduction & Traditional Method of Dinosaur Aging
• [02:07-04:05] — Why Study Crocodiles? Tour at Le Bonheur Reptile Center
• [05:07-06:29] — Marking Bone Growth with Antibiotics, Crocodile Growth Stories
• [07:45-08:31] — Discovering Extra Growth Rings
• [09:03-10:14] — Expert Analysis and Debate
• [10:22-10:46] — Reassessing Dinosaur Age Estimates
• [11:29-11:55] — Do Humans Have Bone Rings?

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Overall Takeaways

• Growth rings in bones can be misleading in both crocodiles and possibly dinosaurs; more than one ring can appear in a single year, depending on metabolic or environmental factors.
• Dinosaur age estimates and growth rates based on ring counting may need to be reevaluated, but “it’s an estimation” (10:22).
• This research highlights the complexity and unpredictability of bone biology, reminding us that paleontology often relies on tentative inferences rather than hard certainties.

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Notable Quotes

• “It's like walking among dinosaurs every day. I'm quite tickled by it, I must say.”
  — Alzette Monkey (04:46)
• “It's all in the bones.”
  — Dr. Anusia Chinsami-Turan (10:44)
• "It's sort of a cautionary tale not to over interpret what we can see and know based on bone tissue under the microscope."
  — Dr. Kristy Curry Rogers (09:54)

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In summary, the episode invites listeners into the thrilling detective work of paleobiology and the ever-evolving puzzle of dinosaur lives, revealing that even our oldest questions can have new, surprising answers—sometimes from the bones of living creatures around us.

Transcript

[Commercial Announcer]

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[Regina Barber]

You're listening to Short Wave from NPR. Hey, Shortwavers. Regina Barber here. Get excited because today we're talking about dinosaurs with science reporter Ari Daniel. Hey, Ari.

[Ari Daniel]

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

[Regina Barber]

Okay.

[Ari Daniel]

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

[Regina Barber]

An academic team building exercise?

[Ari Daniel]

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

[Regina Barber]

Yeah, I was not gonna get that.

[Ari Daniel]

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

[Regina Barber]

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

[Ari Daniel]

It's been a fairly simple process according to Anusia chinsami Taran. 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.

[Anusia Chinsami Taran]

We always thought that these rings are

[Ari Daniel]

formed annually, meaning, like a tree. You might imagine one ring per year.

[Anusia Chinsami Taran]

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.

[Regina Barber]

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

[Ari Daniel]

Well, based on this approach, 20 some years.

[Commercial Announcer]

Whoa.

[Ari Daniel]

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

[Regina Barber]

which we do not have. They died.

[Ari Daniel]

Correct.

[Regina Barber]

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 see birds?

[Ari Daniel]

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.

[Quentin Cronier]

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

[Ari Daniel]

And crocs.

[Quentin Cronier]

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

[Andrea Plass]

Whoa.

[Regina Barber]

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

[Ari Daniel]

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

[Regina Barber]

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

[Ari Daniel]

And I'm R.A. daniel.

[Regina Barber]

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

[Commercial Announcer]

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[Regina Barber]

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.

[Ari Daniel]

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

[Regina Barber]

It sounds awful.

[Ari Daniel]

Well, that's where we're at.

[Regina Barber]

So scary.

[Alzette Monkey]

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

[Ari Daniel]

Alzette Monkey manages Le Bonnier.

[Alzette Monkey]

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

[Regina Barber]

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

[Ari Daniel]

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

[Anusia Chinsami Taran]

Really gorgeous. 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.

[Ari Daniel]

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

[Alzette Monkey]

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

[Regina Barber]

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

[Ari Daniel]

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

[Regina Barber]

Oh, okay.

[Ari Daniel]

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

[Regina Barber]

Okay.

[Anusia Chinsami Taran]

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

[Regina Barber]

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

[Ari Daniel]

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 Perera. And she said it was evident that these four crocodiles had unique growth trajectories

[Maria Eugenia Perera]

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

[Ari Daniel]

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

[Andrea Plass]

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.

[Ari Daniel]

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.

[Regina Barber]

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

[Ari Daniel]

No. The staff says the animals now live out their natural lifespans. But in 2013, when those four crocs were 2 years old, LeBonnier got their leather and Anusia got their bones.

[Anusia Chinsami Taran]

Hi. Hi, Evie.

[Regina Barber]

Welcome.

[Ari Daniel]

Thank you.

[Regina Barber]

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

[Ari Daniel]

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

[Regina Barber]

Okay.

[Ari Daniel]

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

[Regina Barber]

I love the sound of science.

[Ari Daniel]

It's very calming.

[Regina Barber]

Yeah.

[Ari Daniel]

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

[Maria Eugenia Perera]

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.

[Ari Daniel]

Anusia holds one of these slices up to the light.

[Anusia Chinsami Taran]

Look at that. You can see some lines. Look in this area here.

[Ari Daniel]

Yeah. Banding.

[Commercial Announcer]

Yeah.

[Anusia Chinsami Taran]

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

[Regina Barber]

Okay. So what did Anusia and Maria see once they actually did look at it in the microscope?

[Ari Daniel]

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

[Regina Barber]

Huh.

[Anusia Chinsami Taran]

This is a two year old crocodile. And in many cases, we found up to 5 growth marks in the bones. So there were extra growth marks formed during their short life.

[Ari Daniel]

Right. You might have thought they were five years old.

[Anusia Chinsami Taran]

Exactly.

[Regina Barber]

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?

[Ari Daniel]

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 perished than we previously thought.

[Regina Barber]

Right.

[Ari Daniel]

And similar results in other reptiles, as well as Kiwi birds. Back that up as well. Wow.

[Regina Barber]

Okay.

[Anusia Chinsami Taran]

It changes how we Think about how we can use growth marks to determine

[Ari Daniel]

dinosaur growth patterns, suggesting Anusia says that these marks may be better thought of as cycles of growth.

[Regina Barber]

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

[Ari Daniel]

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

[Holly Woodward]

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,

[Ari Daniel]

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

[Holly Woodward]

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

[Regina Barber]

But does Holly have any ideas?

[Ari Daniel]

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.

[Regina Barber]

Okay, okay.

[Ari Daniel]

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

[Christy Curry Rogers]

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 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.

[Regina Barber]

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

[Ari Daniel]

She agrees that there is more work to be done.

[Anusia Chinsami Taran]

For sure, 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.

[Ari Daniel]

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

[Anusia Chinsami Taran]

It's all in the bones.

[Regina Barber]

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

[Ari Daniel]

My pleasure, Gina. Anytime.

[Regina Barber]

Thanks for listening, Short Wavers. And if you like this episode, please follow us on the NPR app or wherever else you may be listening. 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 this story was supported by a grant from the Pulitzer Center. I'm Regina Barber. Thank you for listening to Short Wave from npr. So, Ari, I do have one more question.

[Commercial Announcer]

Shoot.

[Regina Barber]

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

[Ari Daniel]

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 and destroy the presence of previously formed rings.

[Regina 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, right?

[Ari Daniel]

Yep, exactly.

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