How Old Fossils Of Fish Bones Are Revealing New Secrets Of Evolution. : Short Wave Paleontologist Yara Haridy looks at fossilized bones for a living. When she randomly walked by a scientific poster one day, she discovered an entirely new way to take pictures of her fossils. The results are shedding new light on how bones evolved.
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Taking A New Look At Some Old Bones

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Taking A New Look At Some Old Bones

Taking A New Look At Some Old Bones

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You're listening to SHORT WAVE from NPR.


SOFIA: Nothing gets paleontologist Yara Haridy more excited than very, very old bones.

YARA HARIDY: Bones can tell us how old animals got. Bones can tell us how often the animal would go into something like hibernation. It can tell us if the animal laid eggs or not. Like, bones are the libraries of the past.

SOFIA: She's a Ph.D. student at the Museum fur Naturkunde in Berlin, Germany, where she studies bone evolution. She looks at bones that are anywhere from 10,000 to 480 million years old, digging for clues that help explain...

HARIDY: Why do we have bone? Why is bone shaped the way it is? And why does it work the way it does?

SOFIA: And as part of her research, Yara studies osteocytes - cells that live inside the bones of most animals, including us, to help maintain them.

HARIDY: Osteocytes are absolutely the stars when it comes to bones and bone cells. They talk to each other, and they sense pressure. They sense changes in chemistry, and they basically tell the rest of the osteocytes around them if it's all good or if they need to destroy and rebuild. So they definitely are in the middle of all kinds of bone changes.


SOFIA: But here's the kicker - in the fossils that Yara looks at, these osteocytes aren't there anymore. They died a long time ago with the animal.

HARIDY: So what I'm doing is basically studying the ghosts of these cells - the footsteps that are left behind, the shape that's left behind in the bone that is the perfect cast of these cells. So imagine, like, you're going out in the snow, and you flop over, and you start making, like, a snow angel - that snow angel is what I study.

SOFIA: Yara was working really hard to create images of these tiny snow angels in an ancient, jawless fish fossil to better understand how these cells work. But those images weren't really giving her what she needed.

HARIDY: All the big questions I wanted to ask, the technology just wasn't there yet. And so at that point, I was, you know, ready to wash my hands of the whole project and be, like, well, I guess this is for the next generation to figure out. And I had totally hit a wall.

SOFIA: And then, with a bit of luck and the help of her collaborators, Yara figured out a whole new way to look at ancient bones.


HARIDY: I was like, is this real? Nobody had seen fossil cells or cell spaces at this resolution before.

SOFIA: So today on the show, I talk bones with Yara Haridy and learn what led her to create the best images of ancient osteocytes yet and what those images told her about this ancient fish's bones and ours. I'm Maddie Sofia, and this is SHORT WAVE, the daily science podcast from NPR.


SOFIA: OK, so we are here with paleontologist Yara Haridy today. So Yara, before we get into this cool discovery, your Ph.D. is specifically in bone evolution. So what can ancient bones really tell us?

HARIDY: Maddie, what can't they tell us?

SOFIA: (Laughter).

HARIDY: It's true. It's true because it's not just theoretical anymore, you know?

SOFIA: Right.

HARIDY: There's all these amazing models where people will model, oh, this is possibly when flight evolved. Oh, this is possibly when climbing evolved or by - or, you know, being able to walk on two feet evolved. But what bones tell us, these fossil bones, they tell us what actually happened. They're not theoretical.

SOFIA: Yeah, yeah. I'm so - you've got me so excited about bones right now, Yara. I'm like...


SOFIA: I'm like, yeah, bones are the answer to everything, right?

HARIDY: They absolutely are.

SOFIA: Like we mentioned, Yara studies osteocytes, these amazing cells that live in our bones. I mean, they communicate with each other to break down bone, releasing minerals our bodies need - so cool. But remember; Yara is looking at fossils. The osteocytes are long gone. All that's left is the empty space where they used to be. And the traditional methods she was using to look at that space just weren't cutting it for her.

HARIDY: We take a piece of tissue, and we put it on a slide, and we make it really thin so you can shine some light through it and see what it's made of. Now, the problem is when you're trying to look at cells like this, you can only see them in 2D, which is fine if you just want to look at the shape or if they're there or not, but if you're actually trying to figure out how they communicate with one another or how many of them there are in 3D space, it becomes really difficult. It's basically trying to understand what a sphere is when you only have a circle.

SOFIA: Right, OK. But you eventually figured out a way to get very cool images of fossilized cell spaces, but you kind of got this idea by accident, if that's fair to say. Like, you have to tell me the story behind this.

HARIDY: So, Maddie, it was a complete accident. I mean - and by complete accident, I mean, like, it was an accident for me to discover that this method already existed, and people have been using it in battery and material science for years. I'm working with this amazing team at the Helmholtz Institute here in Berlin, and we were working on a completely different, unrelated project. And I was walking down their halls, and I saw this poster that was posted on the wall, and it was by one of my co-authors. And the images on the poster looked like osteocytes; they looked like fossil cells. And I freaked out. I basically - every thought went through my mind. I'm like, are they cheating on me? Are they working with someone else who's doing better work?

SOFIA: (Laughter).

HARIDY: They're standing right beside me, and I grab them. I'm like, what is this? Like, what is this method? Where did you get these images? And they're super nonchalant. And they're like, oh, this? Like, it's just, you know, FIB-SEM, blah, blah - like, something I've never heard of, right?

SOFIA: Yeah.

HARIDY: It was basically, like, alien talk at the time. Like, I have no idea what he's talking about.

SOFIA: So you literally were just walking down the hallway, and you were like, what is that? What did you do?

HARIDY: Yep. Yep.

SOFIA: And they were like, Yara, we do this all the time. You just don't know about it (laughter).

HARIDY: Yeah, 100% - 100%.

SOFIA: OK, so you start, like, working with these material scientists to create these super detailed 3D images of osteocytes. Like, very, very briefly - and understanding my limitations over here - how did this technology work?

HARIDY: Think of it this way - you have a multilayered cake, and you're going to take a slice at a time, and you can reveal the layers at a time. And as you're revealing these layers, you're taking a picture of the new layer that you've just revealed. And you slice the cake again, and you take a picture, and now you have - you know, you can see the new layer. And so having that stack of images, you have all your pictures that you've taken together, you put them in a software that basically makes a 3D model. And the software itself is not new. The machine itself is not new. It's just applying it to fossils - was the new part.

SOFIA: Yara wanted to use this technology to ask some big questions about osteocytes. See; a lot of animals with bones have them but not all. So why did these cells evolve in the first place?

HARIDY: So one of the running theories is, since all the animals that don't have osteocytes are doing everything fine, it must be something inherent to the cell itself. And one of the things that osteocytes can do is basically eat the bone around them and redistribute that mineral back into the bloodstream. And what that means is - its mineral metabolism. It's basically recycling your minerals so it goes into your blood so your muscles and brain can use it because everything from your neurons to your muscles uses calcium and phosphate.

SOFIA: So it's like a little, like, extra supply in your bones for the rest of your body.

HARIDY: Exactly. Your whole skeleton is this battery pack that can be used and reused, and you can actually store minerals back into it. So we know osteocytes do this. But did the very first osteocytes do this? And is that possibly why osteocytes evolved in the first place? Because that would be an incredible advantage over animals that don't have osteocytes - right? - to have this battery.

SOFIA: So using this newly adapted technology, she went looking for very old osteocytes - way back - in an ancient, jawless fish, one of our many distant evolutionary ancestors.

HARIDY: The very first images that we got back had not only the cool cells and everything and had enough of a resolution that we could figure out that, yeah, the cells are connected and, you know, they talk to their neighbors, and they have this many connections, connections comparable to human cells.

SOFIA: Right.

HARIDY: So that was all cool and fun.

SOFIA: Absolutely.

HARIDY: But the best part of our paper was one of the images that we had, one of the cells, had an area around it in the bone that had very low density. So it had less bone around it than the rest of the bone, which was pretty weird and wouldn't make much sense unless you know about mineral metabolism.

SOFIA: Yara literally caught osteocytes breaking down bones in a 420-ish-million-year-old fish, which is very cool and can actually tell us about us and our bones.

HARIDY: It means that not only did that process exist at that time, but it's very likely that it's one of the reasons that bones with osteocytes became the prevailing bone type for millions of years after that.

SOFIA: Scientists had assumed this process of breaking down bone might go back all the way to the very first fish that had bone, but this was actual evidence.

HARIDY: I thought, you know, like - I thought I was the luckiest person, first of all, because it really is luck.

SOFIA: (Laughter).

HARIDY: From seeing the poster on the wall to picking the right specimen to actually being able to see this at a resolution that's understandable is absolutely pure luck. I mean, I want to say I'm a smart scientist and everything. I want to take all the credit, but...


SOFIA: Well, you know, you put them together. A lot of people could walk past that poster, is all I'm saying. A lot of people could walk past that poster.

HARIDY: (Laughter) I really appreciate that.


SOFIA: OK, Yara Haridy, this was so much fun. I - bone convert for life, honestly.


SOFIA: Bones are the answer. That's how I feel.



HARIDY: Thank you so much for having me.


SOFIA: This episode was edited by Viet Le and Geoff Brumfiel, fact-checked by Tyler Jones and produced by Rasha Aridi. Speaking of which, this is Rasha's last episode with us as a full-time SHORT WAVE-r (ph). Rasha, we know you'll keep spreading science joy and sticking up for creepy crawlers everywhere you go. From all of us on the SHORT WAVE team, thank you. We appreciate you so, so much. You're going to do big things, duderino - big things.

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