JUANA SUMMERS, HOST:
This is ALL THINGS CONSIDERED from NPR News. I'm Juana Summers.
SCOTT DETROW, HOST:
And I'm Scott Detrow, and we are considering dinosaurs. What do you get when a team of researchers walks onto a crocodile farm? Answer - a different way of thinking about the age of a dinosaur. Here's science reporter Ari Daniel.
ARI DANIEL, BYLINE: Until now, estimating how old a dinosaur was when it died has been a fairly simple process, says Anusuya Chinsamy-Turan. She's a paleobiologist at the University of Cape Town in South Africa. Just take those fossilized bones and count up the growth rings.
ANUSUYA CHINSAMY-TURAN: We always thought that these rings are formed annually.
DANIEL: Meaning, like a tree, you might imagine, one ring per year.
CHINSAMY-TURAN: Exactly. And then you can plot that and you can work out the growth rate of the dinosaur.
DANIEL: Such plots revealed how dinosaurs likely grew up.
CHINSAMY-TURAN: So, for example, how long did it take T. rex to grow from a hatchling to a fully grown adult?
DANIEL: Answer - 20-some years. But to really confirm this ring counting approach, you'd need to study live dinosaurs. The next best thing are their living relatives, like birds...
QUINTON CRONJE: So we're going on our lovely crocodile tour now.
DANIEL: ...And crocs.
CRONJE: We've got some big crocodiles in here. See the male's head just moved a little bit to this side.
DANIEL: Quinton Cronje is the head animal handler here at Le Bonheur Reptiles and Adventures, an outdoor recreation and education center near Cape Town. A hundred seventy-some Nile crocodiles lurk in the pools beneath a network of pedestrian bridges.
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DANIEL: Chinsamy-Turan snaps photos of the beasts below.
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CHINSAMY-TURAN: Really gorgeous - each of them, their skeletons tell a story about how they grew.
DANIEL: Chinsamy-Turan initially set out to understand how a crocodile's environment impacts its skeletal growth. So she and the team at Le Bonheur injected several year-old crocodiles with an antibiotic over multiple months.
CHINSAMY-TURAN: And the antibiotic actually gets taken up in the development of the bone that leaves a signal in the bone.
DANIEL: Serving as a time marker, essentially. Andrea Plos, a technical officer at the University of Cape Town, came by to measure and weigh the animals. The largest croc grew more than 80 pounds.
ANDREA PLOS: 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 (laughter), so I had to bring in help.
DANIEL: 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. That's no longer the case. But in 2013, when those four crocs were 2 years old, Le Bonheur got their leather and Chinsamy-Turan got their bones.
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DANIEL: Hey there.
CHINSAMY-TURAN: Hi. Hi, Ari. Welcome.
DANIEL: Thank you.
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DANIEL: I paid Chinsamy-Turan a visit at her lab. She rifles through several slides, each one containing a super thin cross section of a crocodile bone. Biologist Maria Eugenia Pereyra prepared the slides, polishing them until the growth rings were beautifully visible.
MARIA EUGENIA PEREYRA: 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 a good one.
DANIEL: When she and Chinsamy-Turan looked at the slices under the microscope, they found something unexpected.
CHINSAMY-TURAN: This is a 2-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.
DANIEL: Right. You might have thought they were 5 years old.
CHINSAMY-TURAN: Exactly.
DANIEL: It's a result that may have implications for dinosaur bones. That is, the crocodile findings suggest at least some dinos may have been younger when they perished than previously thought. Similar results in other reptiles as well as kiwi birds back that up.
CHINSAMY-TURAN: It changes how we think about how we can use growth marks to determine dinosaur growth patterns.
DANIEL: Suggesting, she says, that these marks may be better thought of as cycles of growth. The results appear in the journal Scientific Reports. Holly Woodward is a paleohistologist at Oklahoma State University who wasn't involved in the research.
HOLLY WOODWARD: Studies like this one are really important in adding to that body of knowledge of how often growth rings can be reliable.
DANIEL: But Woodward doesn't believe the matter's settled, since some animals show annual growth rings, while others don't.
WOODWARD: It was very weird, but we can't yet say why or what causes it specifically.
DANIEL: And until we do so, Woodward argues it's premature to throw out using growth rings as annual age markers. For her, that's at least a starting point for understanding dinosaur growth. As for Anusuya Chinsamy-Turan, she agrees there's more work to be done, but she believes the answers may well be waiting for us.
CHINSAMY-TURAN: It's all in the bones (laughter).
DANIEL: For NPR News, I'm Ari Daniel, Cape Town, South Africa.
DETROW: Ari's reporting for the story was supported by a grant from the Pulitzer Center. Transcript provided by NPR, Copyright NPR.
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