Dinosaur mysteries with Riley Black

Summary

Unexplainable – "Dinosaur Mysteries with Riley Black"

Host: Bird Pinkerton (Vox)
Guest: Riley Black (science writer, amateur paleontologist)
Date: July 20, 2026

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Main Theme & Purpose

This episode explores how paleontologists construct stories about dinosaurs from incomplete and ancient evidence. Featuring prolific science writer and amateur fossil-hunter Riley Black, the conversation dives deep into the mysteries of dinosaur reconstruction, the limits of what fossils can reveal, and the tantalizing pieces of prehistoric life that trace fossils and coprolites (fossilized poop!) provide. With a mix of wonder, humility, and humor, the episode demystifies paleontology’s detective work and celebrates the ever-evolving picture of dinosaur life.

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Dinosaur Bones: Foundations and Limits of Knowledge

• How Fossil Interpretation Began

  • Early science in the 1700s married geology and comparative anatomy (04:00).
  • “People find these weird bones, usually disarticulated, usually incomplete, but it’s just big, big stuff… A tooth from a reptile that’s far larger than any crocodile or snake or anything that lives in that part of the world today.”
    — Riley Black (03:59)

• Imagination and Hypothesis in Reconstruction

  • Most dinosaur skeletons are partial; paleontologists extrapolate missing pieces from close relatives. Brachiosaurus, for example, is assembled from “forelimbs and parts of the vertebra and some of the neck, and that’s about it. So we’re really basing it on other more complete animals.” (04:46)
  • “Anytime you see a complete dinosaur, unless it’s really literally that specimen… it’s a hypothesis.”
    — Riley Black (06:16)

• Iconic Examples: T. Rex Hands & Evolving Models

  • Discovery of T. Rex’s reduced two-fingered hand changed prior models (07:58).
  • The “splint” bone—a tiny remnant—shows evolutionary shifts in the lineage (07:31).
  • “We always make fun of T. Rex for having tiny, tiny hands… They used to have three fingers and their ancestors lost them.” — Riley Black (07:46)

Bizarre Dinosaur Structures and Unanswered Questions

• Alvarezsaurids — Mysterious Tiny Arms

  • Mononykus: long legs, tiny one-clawed arms (09:08)
  • “It’s just one claw. That’s what its name means, is one claw.” — Riley Black (09:30)
  • Theories: anteater analog (digging into termite mounds), egg grasping (10:09–11:02)
  • “You look at that stubby arm, it’s just kind of like, what?” — Riley Black (11:02)

• Fashion Statements: Triceratops Horns, Sauropod Sails

  • Dino ornamentation possibly for species identification or sexual selection
  • Sailed-back dinosaurs like Ouranosaurus: “It has a sail on its back… communicating to other members of their species saying, ‘I’m bigger than you or I’m an adult or I’m a juvenile’…” (13:36)
  • “Always peacocking. In the early Cretaceous.” — Riley Black (13:56)
  • The functions of these structures remain mostly speculative (12:54, 14:30)

Beyond Bones: The Power of Trace Fossils

[15:21–16:14]

• Trace Fossils—What Are They?

  • Tracks, tooth marks, coprolites, even beetle burrows—anything made or left behind by animal activity (15:27)
  • “It’s the marks that animal made in life. So we’re talking about things like tooth marks and tracks and fossil feces…” — Riley Black (15:27)
  • These reveal moments of actual behavior: direction, speed, even injuries.

• Stories from the Field

  • Riley shares stories of finding aetosaur tracks and early-dinosaur footprints in Utah (19:02–21:25).
  • “It looked like the ground was giving me a high five… Just those three toes at the claws at the ends.” — Riley Black (20:03, 21:07)
  • Trackways can indicate speed, social behavior, and even injuries—like a limping Allosaurus (21:33).

• Rewriting Dinosaur Life Histories

  • Trace fossils show life’s messy side: scavenging, injuries, even beetle damage (23:46–24:21).
  • “We can tell from where those bite marks are sort of what were the favorite parts of, like, a sauropod body… they were going in through the cloaca to get at the pelvis after they’d taken off the other tail meat…”
    — Riley Black (23:46)
  • Discovery: Dinosaur bones sometimes lay exposed for months/years before burial, contrary to the idea of rapid fossilization (24:32).

Traces Answering Skeleton Mysteries

• Coprolites and Claws: Solving Ancient Mysteries?

  • The diets and lifestyles of dinosaurs like Alvarezsaurids might be revealed by fossil poop or scratched termite mounds (25:41).
  • “We actually have scratches made by dinosaurs in the fossil record… There is a mammal burrow that has claw prints from a velociraptor-like dinosaur…” — Riley Black (25:41)
  • Coprolites can show diet directly: “There’ll be more coprolite fossils than skeletal fossils, because they’d be making them all the time… and they should be full of little ants or termites or something like that.” (26:44)

• Identification Challenges

  • Often, coprolites can’t be definitively assigned to a species unless found with the skeleton (27:32–28:15).
  • “It goes back to what you were saying at the beginning. For anything that we find in the fossil record… Here’s a dozen questions.” — Riley Black (28:15)

Curiosity and the Future of Dinosaur Science

• Why Keep Chasing the Unknown?
  • “There’s always something more to learn. There’s always something that I didn’t know. Nature is so surprising.” — Riley Black (28:22)
  • New techniques have let scientists discover dinosaur colors, something thought impossible just decades ago (28:22).
  • “In a way, it didn’t kill the magic, it just made it more interesting.” — Riley Black (28:51)
  • Paleontology is participatory: “If you can put boots on and go look for fossils or even just, like, volunteer in a museum poking through drawers, you can change the way people see ancient life.” — Riley Black (29:41)

Book Recommendation

• The Last Days of the Dinosaurs
  • “So if you really want to get a feel for not only what it’s like to be there in the Mesozoic, but the way that I think a paleontologist sees the world… that’s the best place to start.” — Riley Black (30:07)

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Notable Quotes & Moments

• On Dinosaur Iconography:

  • “The dinosaurs are dead, yet in our imaginations, they are very much alive.” — Riley Black (01:11)

• On Scientific Humility:

  • “Here’s a dozen questions.” — Riley Black (28:15)
  • “Even familiar animals, even the most basic questions about dinosaurs, we don’t necessarily have answers for yet.” — Riley Black (28:22)

• Humor & Humanity:

  • “You look at that stubby arm, it's just kind of like, what?” — Riley Black (11:02)
  • “[They were] always peacocking in the early Cretaceous.” — Riley Black (13:56)
  • On Allosaurus feeding through the pelvis: “Sorry to be crass. The butthole.” — Bird Pinkerton (23:46)

Key Timestamps

| Timestamp | Topic / Quote | |-----------|---------------| | 03:59 | Early fossil interpretation, origins of paleontology | | 04:46 | Brachiosaurus as an example of incomplete skeletons | | 06:16 | “Anytime you see a complete dinosaur… it’s a hypothesis.” | | 07:31 | T. Rex's vestigial third finger | | 09:30 | Alvarezsaurids and their mysterious “one claw” | | 13:56 | “Always peacocking in the early Cretaceous.” | | 15:27 | Trace fossils explained | | 19:02 | Field discoveries of trackways | | 21:33 | Trackways showing dinosaur injuries (limping) | | 23:46 | Scavenging behaviors interpreted from bite marks | | 25:41 | Coprolites and scratch marks as behavioral clues | | 28:22 | Curious drive and discovery of color in dinosaur science | | 29:41 | Paleontology's openness to amateur participation |

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Summary

This episode of Unexplainable with Riley Black perfectly captures paleontology’s mix of tough detective work, wild curiosity, and vibrant imagination. While skeletons form the backbone (pun intended) of our knowledge, much remains speculative, and it’s the traces—footprints, scars, poop, and more—that give us rare, real glimpses of dinosaur lives. New discoveries revise the stories we tell, and Riley’s infectious enthusiasm is a reminder that the science of deep time is for everyone curious enough to ask, “What don’t we know?”

“There’s always something more to learn. Nature is so surprising.”

— Riley Black (28:22)

Transcript

[Riley Black]

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[Bird Pinkerton]

This Monday.com ad was created by a team of people and AI agents. The agents wrote the copy and managed the timelines while our human creative director made sure it all made sense. Easy. Create your own AI agent today on Monday.com how do we know what we know about dinosaurs? I think about this whenever I'm in a natural history museum because you have these bones that are tens or even hundreds of millions of years old. They come from a version of our planet that looks pretty different from the earth that we walk on today. So how do we take these fossils and spin them into the stories about dinosaurs that I love to read and watch?

[Riley Black]

The dinosaurs are dead, yet in our imaginations, they are very much alive.

[Bird Pinkerton]

My guest today, Riley Black, has written a lot about how to piece together an entire narrative from fossils. Riley writes about how we know what we know about dinosaurs. Riley, thank you for being on the show.

[Riley Black]

Oh, my pleasure. I mean, you asked me to show up and bring my dinosaur stuff. How could I resist?

[Bird Pinkerton]

For our listeners, Riley brought some dinosaur models and a cast of a dinosaur hand along. But Riley, can you tell me a little bit about who you are, please, and what you do?

[Valerie Shenkman]

Sure.

[Riley Black]

So I'm a professional science writer. I've written about a dozen books about prehistoric life in one form or another. And I'm also an amateur paleontologist. I go out in the field and actually find some fossils.

[Bird Pinkerton]

I mean, if you are going out into the field, what is amateur about it?

[Riley Black]

So there's a bit of a divide sometimes between the professional paleontology side and the many, many, many amateurs and volunteers out there looking for fossils. So I call myself an amateur because I'm not a curator or I'm not a professor, but I've been out in the field from places from Alaska to Mexico. A lot of work in the four Corners, actually finding fossils that go to museums and are cataloged and studied there. So I do it for the love of it.

[Bird Pinkerton]

But why dinosaurs?

[Riley Black]

It's hard not to be into dinosaurs. I mean, so from what I was told, I went through a very short phase of trucks and Then elephants, which I still love, and dinosaurs. So big and loud, I guess, is always what I've been kind of into. Went to the American Museum of Natural History when I was five. Heard of it when you are small, not as small as a Mesozoic mammal, but still quite small. And seeing these big skeletons, it's hard not to be impressed. And what I love about them, and really any prehistoric life, is you look at their bones or their traces or what they leave behind, and there are all these questions of how did they move, what did they look like, what color were they, what did they sound like, what did they smell like? All of the stuff that we may or may not have answers to. So it was a chance to get to know this whole realm of science that's fueled by the questions where you're encouraged to use your imagination.

[Bird Pinkerton]

I think this is a perfect transition into what I wanted to talk to you about today, which is how do we know the things that we know about dinosaurs? And so I thought maybe we could start sort of where the paleontologists first started, which is the skeletons that they left behind. So talk to me about how we sort of take a dinosaur skeleton, like a bunch of bones, and turn that into a story about reptiles running through the world.

[Riley Black]

I mean, this is how paleontology as a science started. I think it's important to note that people have been finding fossils for thousands and thousands of years. We have, like, stone hand axes of the fossils in them. Indigenous cultures all over the planet have encountered fossils of different kinds and understood that these were once living things. So, like, we've had this long recognition that there was life before us. But it's the late 1700s. We have geology, which is starting as a science, and comparative anatomy, mostly in Western Europe. And you put those two things together, people find these weird bones, usually disarticulated, usually incomplete, but it's just big, big stuff, like a tooth from a reptile that's far larger than any crocodile or snake or anything that lives in that part of the world today. And they know this must be something, and they try and slide it into what they knew. So this is why the earliest representations of dinosaurs look like giant lizards or giant crocodiles. It's just like, what's a reptile? But it must have been 100ft long. Then we get more complete skeletons, like, oh, okay. The body shape is entirely different, which is kind of funny. Brachiosaurus is a great example because we really only have the forelimbs and parts of the vertebra and some of the neck, and that's about it. So we're really basing it on other more complete animals.

[Bird Pinkerton]

Wait, wait, this dinosaur?

[Riley Black]

Yes.

[Bird Pinkerton]

We have like these parts, like the front legs, some of its neck and what else?

[Riley Black]

A few bits of its backbone along the spine, a couple limb elements and that's it. There's some that I know are undescribed. There might be skull pieces.

[Bird Pinkerton]

How do we make something like this? From some forelimbs, some vertebrae, some other bones and a dream.

[Riley Black]

Yeah. How we get to something like this, our friend uses for us here.

[Bird Pinkerton]

So you're showing me right now a model you have of a beautiful long necked dinosaur with a long curving tail, four lovely long legs, red and green

[Riley Black]

coloring for something like Brachiosaurus, where we don't have the whole skeleton. Even now we look to their closest relatives. There's a related animal called Giraffatitan that's found in Giraffe and Titan. Sorry, so like giant giraffe.

[Bird Pinkerton]

Giraffe, yeah.

[Riley Black]

We have the arm lizard and we have the giant giraffe. Giant giraffe is more complete and we can. They're close enough that, you know, we know that they must have had similar bones. Like this is something like. We know there are vertebrates, right, Based upon the bones that we find. So when you have a vertebrate, they must also have a circulatory system and a nervous system and skin. Even if we don't have the exact fossil, we can start filling in those pieces as a hypothesis. So anytime you see a complete dinosaur, unless it's really literally that specimen or that cast that someone's made a one to one of, it's a hypothesis. Anyone's vision of a dinosaur, like I can say T. Rex. And the T. Rex I see in my head is gonna be different from what you see in your head. And this is what I love about it, is that we're taking sort of this bare scaffolding and based upon what we know and what we see from experience, filling in what might have been there.

[Bird Pinkerton]

What are some of the most interesting or maybe even counterintuitive ways that we have been able to say no, I'm pretty sure this looked this way just by looking at the bones alone.

[Riley Black]

So the bones alone, usually we need a complete skeleton or a fairly complete skeleton to tell, but this little T. Rex hand that I brought in is a really good example. This is an animal that would have been more than 30ft long and you can hold its hand in your hand. It would have been on an arm about as long as yours.

[Bird Pinkerton]

So I'm looking at, just to be clear, sort of what looks like two fingers of a T Rex hand that have very pointy claws on the end of them.

[Riley Black]

And you actually have a little bit of a third finger there. So there's a little splint bone that's underneath the larger fingers. And that third one, that splint is the remainder of the third finger. We always make fun of T Rex for having tiny, tiny hands. Right? Well, they used to have three fingers and their ancestors lost them.

[Bird Pinkerton]

So this tiny little bone, this like, this bone that's actually the size of my pinky is like an ancestral third finger, like a tailbone of a third finger that they have, which was lost.

[Riley Black]

And we didn't know that. So when the first Tyrannosaurus rex was being reconstructed here in New York City, we used to think it was related to other carnivorous dinosaurs that we knew about. But there was no arm. We had the big old skull, we had the backbone ribs, all this stuff. No arms. The arms are tiny. Of course, they'd probably wash away and not get buried. It wasn't until someone actually found a T Rex arm with the hand at the end of it. So early on they thought, well, that's three fingers, like all the other carnivorous dinosaurs do. And then someone found a related form in Canada and Alberta that only had two. And we know that they were closer to T Rex. It's like, okay, we have to change the model. And that's why T Rex has two little fingers.

[Bird Pinkerton]

Fascinating. Okay, so finding bones, finding more bones to complete out a skeleton can really tell us, like, oh, we got this wrong, we got this wrong, et cetera. But you also had a. You had an article that you wrote that was also about tiny arms that was a little different that I loved. Can you tell me a little bit about Alvarezaurus? Am I saying that right?

[Riley Black]

Yes, yes. The Alvarezaurs, I'm glad to talk about them because nobody talks about Alvarezaurs. This is like the indie band that, like, only does vinyl. So let me pull up a photo.

[Bird Pinkerton]

Show me a picture of Alvarezaur, please.

[Riley Black]

This is a little critter called Mononychus.

[Bird Pinkerton]

Oh, this is Mononychus, and it belongs

[Riley Black]

to a group called Alvarezaurs.

[Bird Pinkerton]

So I'm looking at this very small, very cute creature that has very long legs, it has a really long neck, and then it just has these rinky dink little arms coming off of it that it's holding together in a little.

[Riley Black]

Oh, like a little please, like a begging posture. Like, can I go home an hour early kind of pose. That's just one claw. That's what its name means, is one claw.

[Bird Pinkerton]

So what is its one claw for?

[Riley Black]

We don't know. We don't know because the skeleton can't really tell us exactly what it's for.

[Bird Pinkerton]

Right.

[Riley Black]

In that it can give us the range of motion and we can reconstruct the musculature and things like that, but it can't really tell us what did it use that musculature for? How did it move those limbs? If we know it has a short range of motion, then to what purpose, what function?

[Bird Pinkerton]

Are there ideas? Do people have theories? Okay, love a theory.

[Riley Black]

So my favorite one is that these were dinosaur anteaters because they often have either no teeth or very, very, very small teeth. And this is something that we see happen with like a shift away from carnivorous foods and more towards, like insects and plants and things like that. But we think that they were like anteater dinosaurs, using those little claws to basically stick their chests to the ground and just kind of scratch away at ant and termite mounds, which we know were around at the time. We actually find dinosaur bones sometimes with termite damage to them.

[Bird Pinkerton]

So theory one is they were anteaters, just like poking their fingies in there. What are the other theories for what these tiny claws could be for?

[Riley Black]

They might have been for grasping eggs. There was a species that was named a few months ago that they thought that they were just kind of clasping eggs to their chest. They're just kind of doing a little dip, picking up an egg and kind of skittering away with it.

[Valerie Shenkman]

Okay.

[Riley Black]

And that's really about it so far. We don't really like it. You look at that stubby arm, it's just kind of like, what? And there's not a whole lot else. We don't have a lot of equivalence for arms like these other than animals that dig into the ground somehow.

[Bird Pinkerton]

Okay, so we have T. Rex claws, we have Alvarezsaur claws. Are there other sort of dinosaurs where we're just sort of like, well, we have a bunch of bones. What could this possibly be? What does it look like?

[Riley Black]

So dinosaurs love their bizarre structures. Like the fashion through the Mesozoic was just something else, like the ornamentation on these animals constantly. Like our little Triceratops friends. Even though that's a very traditional three horned face look, there are lots of horned dinosaurs with all these different arrays of horns and spikes and hooks and everything else that help them differentiate each other and that we have a fair handle on. But in terms of ornamentation, there are dinosaurs with like sails on their backs and we have no idea why.

[Bird Pinkerton]

Sails?

[Riley Black]

Yes, sail back dinosaurs. So there's one in particular called Ouranosaurus. This is an herbivore, so everybody knows Spinosaurus, that got its name for the spines on his back. Right.

[Bird Pinkerton]

We're doing indie dinosaurs here.

[Riley Black]

We're not doing the it girl like on the COVID of Nat Geo. We're doing, again, the deep cuts. So this is an Ouranosaurus. It is something related to Iguanodon or the duck beaked dinosaurs. And it has a sail on its back.

[Bird Pinkerton]

Okay. So I'm looking at a dinosaur. It's very difficult to describe. So the middle part of it sort of looks like a regular dinosaur. And then on its back it just has like a whole fan of bones coming out. So I see what you mean now about a sail. What? I feel like I know the answer. And the answer is we don't know. But what's the sale for we don't know?

[Riley Black]

Amazingly enough, there have been a few ideas, one of which, one of my favorite sort of discarded hypotheses is that we see these long neural spines, so these flat bones that come up off the backbone in things like bison or various mammals. And they usually hold, pull the hump, or the end of a ligament that goes from the back of the head to between the shoulders. Because a lot of these mammals have big heavy heads. They need like an extra basically rubber band to help them keep their heads up. And we used to think that this was true for the dinosaurs as well. But then you'd have this basically mound shaped dinosaur with legs. If you imagine like a little hill with legs kind of shuffling around, that's more or less what they would look like. But that was one of the ideas, that this is some sort of head support or something like that.

[Bird Pinkerton]

Okay.

[Riley Black]

What seems more likely is it's some kind of billboard. Basically it's dinosaur advertising that there's communicating to other members of their species saying, like, I'm bigger than you or I'm an adult or I'm a juvenile, or like different dinosaur sexes.

[Bird Pinkerton]

Like a peacock tail almost, but on their. A permanent peacock tail on their back.

[Riley Black]

Yes. Always peacocking. In the early Cretaceous. Yeah. And with something that's that big and that elaborate and it takes energy to grow. Right. This is an investment this animal is making. Bone is constantly remodeling itself. It must have had formed some purpose in this animal's life. But unless we can see These dinosaurs interact, it's very difficult to tell what they were doing. Now, there's some ways that maybe we can get at it. If we can find some skin and find out what color that skin was, which is the thing we can do now, maybe we can start to get at it. But again, it takes the luck of the fossil record to actually make such a find.

[Bird Pinkerton]

Got it. So if you could find skin from another part of its body and then skin from this, and the skin on the sail was like neon, and the skin on the rest of its body was, like, fairly gray, it would be relatively clear. And the neon sign said, like, two for a dollar at Spinosaurus Land. You'd be like, oh, it's a billboard.

[Riley Black]

Yeah. Got that vaporwave aesthetic going on the sail.

[Bird Pinkerton]

Amazing. So what you've told us to this point is essentially that skeletons can't tell us everything we need to know. Bones are not the be all and end all. We still have a lot of questions. We have questions about the sails on dinosaurs like Ouranosaurus or even Spinosaurus or what Alvarezsaurs use their claws for. What else can we look at to understand dinosaurs in more depth?

[Riley Black]

Yes. So you're getting to one of my favorite kinds of fossils, and those are trace fossils.

[Bird Pinkerton]

Trace fossils, yes.

[Riley Black]

So these are things that animals leave behind in the fossil record. So it's not the tooth of the bone or whatever itself, but it's the marks that animal made in life. So we're talking about things like tooth marks and tracks and fossil feces and all these other things that basically an animal leaves behind just through living. It's interaction, it's behavior. So, like, when you see a dinosaur trackway, it's not just footprints in the rock that is moments in that animal's life. And we can calculate, like, how tall it was, how fast it was moving, maybe the direction it was going in. Is there another animal and nearby, is it going in a certain direction, like to get around an obstacle or to avoid something? So these are actually like moments of prehistoric time that we still have as fossils.

[Bird Pinkerton]

More on that after the break.

[Valerie Shenkman]

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[Bird Pinkerton]

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[Valerie Shenkman]

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[Bird Pinkerton]

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[Riley Black]

Make our paycheck more colossal or we'll poop on all the Colossals.

[Bird Pinkerton]

Yes. What's your like, what's one of your favorite? Already pulling out the phone to show me something.

[Riley Black]

Well, now I get to brag a little. I get to talk about stuff that I have found out in the field.

[Bird Pinkerton]

What's one of your favorite traces?

[Riley Black]

One of my favorite traces. So what I'm showing you on the phone is it kind of looks like multiple toes there. You can see 1, 2, 3, 4.

[Bird Pinkerton]

Yes.

[Riley Black]

And then there's a couple small toes next to it. So it's basically the front foot and the back foot of a crocodile like armadillo thing called an aetosaur.

[Bird Pinkerton]

Okay, aetosaur. How do you know? Just is it like that's what matches up that footprint?

[Riley Black]

Yeah. So you can look at the skeletons and you can look at what other animals are found in that formation and see kind of whose foot matches what print. It's rarely one to one unless an animal literally Dies in its tracks, which sometimes does happen. It's hard to be 100% certain, but in this case, the hand and foot anatomy matched this armadillo, like crocodile relative, that was herbivore that was living around when dinosaurs were really small. And just kind of. It looked like the ground was giving me a high five. It was, like, impossible to mask.

[Bird Pinkerton]

And so how did you find this?

[Riley Black]

Yeah, so I was out on an expedition with the Natural History Museum of Utah out in the eastern part of the state. So, like outside Arches national park, that kind of area, desert country, you're miles and miles from anybody, and the rocks are very, very ancient there. So we're talking about the end of sort of the dawn of the dinosaurs, the Triassic, about 220 million years ago. You hop out of the truck, you have your water and everything that you need for the day, and you just go walking and looking for fossils. So I start picking around the rocks nearby, and you have to look at these walls of rock and kind of determine what layers you're going to look at, where you're going to go, like the angle of the sun. That can matter in terms of what you're going to find. And I start picking along and I find these little invertebrate traces, basically, little like beetle footprints. And it's like, okay, there are traces here. So I find those little beetle traces. I find a little plant fossil, and then there's a dinosaur track. I actually have brought one of the photos of that one as well. And this was, like, indisputable. That's what it was as soon as I saw it.

[Bird Pinkerton]

So I'm showing this. So I'm looking at what is it. Looks like a footprint.

[Riley Black]

Yeah, just looks like a little chicken track. It was about that size, really. Just those three toes at the claws at the ends. And then I start taking my field notes and start looking for other stuff. And I see that footprint from the Aetosaur, as well as a whole bunch of other ones. Like now I'm just reliving this trip, basically having a happy little flashback here.

[Bird Pinkerton]

But so you have these footprints. What can those footprints tell you?

[Riley Black]

Yeah, so footprints can tell you an animal's moving speed. There's a relatively simple calculation that you can use between foot strides to tell how fast it was likely moving longer apart usually means it's moving quicker. It's really basic animal physics kind of stuff. One of my favorites. It's not at this site, but it's at a place nearby where I found those tracks. It's a Jurassic age Site that has tracks that were likely made by an animal like Allosaurus. So think like a Jurassic T. Rex. Just three fingers a little bit smaller, and the stride lengths on one foot are different than the other. And what that means is that dinosaur's limping, so it got injured somehow. And we have an injured dinosaur trackway. And we don't entirely know what caused it, but it's just a great reminder of, like, these animals dealt with the same kind of, like, injuries and bone breaks and everything that we see in animals now.

[Bird Pinkerton]

They were. They were living lives. They were not sort of perfect specimens of dinosaur hood. They were. Each one was an individual dinosaur with its own little trials and tribulations, I guess. Is there something that trace fossils have helped us? Are there ways that they've sort of changed our understanding of some of the skeletons that we've received or sort of upended things that we thought we understood about dinosaurs?

[Riley Black]

Absolutely. So trace fossils are not just for dinosaurs. All sorts of prehistoric things left traces and. And including traces on dinosaur fossils. So there's a place in western Colorado called My Gut Moore Dinosaur quarry. It's like 150 million years old. This is, like, heyday of Allosaurus, Stegosaurus, Apatosaurus, like, all those favorites. But everything there is in a jumble. So we don't get complete skeletons out of that site. It's basically this pond where things were disarticulating and falling apart and scavengers came by. There's so many bite marks on these fossils. You see the ends of thigh bones. They're just raked with these teeth from all the feeding and stuff on. And we can tell from where those bite marks are sort of what were the favorite parts of, like, a sauropod body. So if you have an Allosaurus coming to scavenge, where is it gonna start? Some of it suggests that they were going in through the cloaca to get at the pelvis after they'd taken off, like, the other tail meat and stuff.

[Bird Pinkerton]

So they were going in through. Sorry to be crass. The butthole.

[Riley Black]

Yes, they were.

[Valerie Shenkman]

Yeah.

[Riley Black]

Yeah. They would enjoy, like, basically, you know, there's a big tail muscle called the cauda femoralis that they take that stuff first, and when they're down on, like, the prime cuts, that's how they got into the rest of it.

[Bird Pinkerton]

I'm such a child.

[Riley Black]

So we have those bite marks on those bones, but we also have beetle damage. So a lot of museums use, like, dermestid beetles to clean their skeletons. Right? You have a skeleton, you Want it to be clean for display. You put it in with the beetles and then you take it out before the beetles start to burrow into it. Because that's what they want to do. They want to.

[Bird Pinkerton]

Sorry, I love that you were saying this just sort of like casually. And we all know, sorry, they use beetles to clean. Okay, great, yes, fact I learned. But yes.

[Riley Black]

So those beetles, normally to complete their life cycle, they want to burrow into that bone. So naturally that's what tends to occur. And that's what we find on some of these dinosaur bones, that they were exposed now in the open long enough that those beetles were like basically eating their way through the bone, leaving trails in them, which tells us those bones were exposed on the surface for a while. So this whole idea of we need quick burial to make a dinosaur fossil, probably not true. Some of these bones were on the surface for months to even years before they got buried. Which makes sense because even though we have our pint sized Brachiosaurus in front of us, the real animal would have been about, you know, like 60ft long and weigh upwards of 20 tons. Takes a lot of sediment to bury something like that. So by looking at what the insects were doing, the traces that they left, it's the same kind of stuff that forensic investigators use today to kind of determine how long a body has been exposed. We can do that with dinosaurs thanks to traces.

[Bird Pinkerton]

So if we return to sort of the questions you were laying out at the beginning about say like Alvarezaurus, why does it have such tiny little finger claws? Could trace fossils potentially help us kind of answer the questions that are posed by these skeletons?

[Riley Black]

Yes, because one of the things that we always want to know about dinosaurs, right, is what did they eat? And so often when it comes to the teeth and claws and other things, it comes down to a question of feeding and how are they acquiring that food and how are they processing it? So we think of our little Alvarez or friends, a little friend like Mononykus, if they were sticking their chest against an ancient termite mound, which also like, ow, I hope they don't bite. This sure is a strategy to pick and digging away with their arms. We might be able to find a prehistoric termite mound that has scratch marks in it. We actually have scratches made by dinosaurs in the fossil record from Utah, in different part of the state than I was prospecting in, there is a mammal burrow that has claw prints from a velociraptor like dinosaur. Basically digging in that this dinosaur is trying to dig into the burrow to Pull the mammals out. So we could find something like that with Alvarezsaurs, these claw scratches on the insect mounds, and that would give us some clues. More likely, we're going to get the answer through fossil poop. Coprolites. So coprolites, that's a kind of trace fossil. It's basically what an animal is eating. It's the remainder of the gut contents. Sometimes we get gut contents, sometimes we get something called a cololite, which is basically when it's in the intestine but hasn't exited yet. Coprolite is just fossil poop, usually contains. If there were scales or exoskeletons or anything like that, it would be in there. So if Alvarezsaurs were eating these little insects, we should be able to find a coprolite from them. There'll be more coprolite fossils than skeletal fossils, because they'd be making them all the time, basically, back in the Cretaceous, and. And they should be full of little ants or termites or something like that. Or maybe we'll look into them and find eggshell or little mammal bones or who knows what. But that would be the test of the actual animal's behavior. We can look at their skeleton and say, like, maybe they did this, but traces, like, basically to halve the remainder of what they actually ate.

[Bird Pinkerton]

How would you know it was an Alvarezaurus coprolite?

[Riley Black]

That's a great question, because you wouldn't really be 100% sure except if it were exceptionally rare. So most of the time we find coprolites just by themselves. They're just individual fossils. And we can say, okay, the body size matches, or based upon what we've collected for other animals, it seems like it came from a similar sort of animal. If we found it as a cololite or found it associated with a skeleton, then you could say, like, okay, these are close together, you know, like there's some kind of association between them. So it's probably that might be able to look at the geochemistry. But here's the thing, right? Like, it goes back to what you were saying at the beginning. For anything that we find in the fossil record, it's like, find one fossil. Here's a dozen questions.

[Bird Pinkerton]

And what, I guess, what keeps you interested in sort of trying to piece everything together?

[Riley Black]

There's always something more to learn. There's always something that I didn't know. Nature is so surprising. Even familiar animals, even the most basic questions about dinosaurs, we don't necessarily have answers for yet. But in my lifetime, the amount of things that we've learned that. I was told even as a kid, we were never, ever going to know. For example, dinosaur color used to be, you know what? Do whatever colors you want. Nobody knows what color dinosaurs were. Make that neon pink T. Rex or Stegosaurus with bright yellow plates or what have you. Now we're starting to find out what colors they actually were by comparisons to modern birds and looking at skin and feathers and the microscopic nature of it, that creates structural color. So in a way, it didn't kill the magic, it just made it more interesting. Okay, we got some color now. What other colors were there? What color patterns were there? Did they vary between different sexes or populations or species? So all of this curiosity, it's incremental and cumulative and it changes our perception of what the ancient world was like. I love the fact that the dinosaurs that I grew up with, especially seeing older documentaries and books and out of date museum displays, are now fundamentally different. It's the same species, sometimes the same skeletons, but they're rearranged, they're brought to life in a different way. And it feels like something that everybody can participate in. And I love that paleontology can be welcoming in that way, that it's something if you can put boots on and go look for fossils or even just like volunteer in a museum poking through drawers, you can change the way people see ancient life.

[Bird Pinkerton]

Love that. Riley, thank you for so much for coming on talking to us about dinosaurs. If people want to read your books, which one would you recommend that they start with?

[Riley Black]

I would recommend the Last Days of the Dinosaurs.

[Bird Pinkerton]

Okay.

[Riley Black]

It is the first narrative book that I wrote. So this is like if you were there 66 million years ago, you're standing in ancient Montana. From the day before the asteroid hits through the first hour, the first day, the first week, through the first million years, as you see life change, it's basically the making of the world as we know it now, the reason why we're here. So if you really want to get a feel for not only what it's like to be there in the Mesozoic, but sort of the way that I think a paleontologist sees the world, the way that I see the world when I'm out in the rocks, when I'm looking for these animals, the kind of visual mental landscape that you kind of create from what you know, I think that's the best place to start.

[Valerie Shenkman]

All right.

[Bird Pinkerton]

Riley Black. They are a science writer, amateur paleontologist, and a wonderful guest. So thank you so much.

[Riley Black]

Oh, it's been a joy.

[Bird Pinkerton]

If you want to know more about Riley's books, we will link to their website in the description for this episode. This episode was produced by Valerie Shenkman and me, Bird Pinkerton. It was edited by Joanna Solotarov. Our video editor is Alex Coles. Our animator is Karim Correa. Our fact checker is Melissa Hirsch. Our studio engineers are Davon Howard and Joe Nebras. Mixing and sound design by Christian Ayala. Music from Noam Hassenfeld and Meredith Hodnot runs the show. Special thanks as always to Brian Resnick for co creating the show with me and Noam. And if you want to see the video version of this episode, you can find us on Netflix. If you have thoughts about the show, we would love to hear from you. Please email us@ unexplainableox.com or if you'd like to support the show, join Vox. Become a Member just go to vox.com members and if you signed up because of us, please let us know and thank you. Unexplainable is part of the Vox Media Podcast Network and we'll be back soon.

[Riley Black]

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[Bird Pinkerton]

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