North America's oldest pterosaur fossil

[MUSIC] Welcome to Science Sessions, the podcast of the proceedings of the National Academy of Sciences, where we connect you with Academy members, researchers, and policymakers. Join us as we explore the stories behind the science. I'm Paul Gabrielson. More than 200 million years ago, fragmentary skeletal remains of a community of amphibians, reptiles, and tarisars were concentrated and buried by a sudden flow of debris down a river channel in what is now Arizona. In a recent PNAS study, K. Barron's Meyer and Ben Kligman of the National Museum of Natural History and Colleagues, studied the fossilized remnants of this community to understand how these animals, including a previously undescribed tarisore, formed an ecosystem in the lead up to a cataclysmic extinction event. The results also offer insight into the early ecology and evolution of tarisars in North America. K. Ben, tell us about the fossil assemblage you studied. Why is it so remarkable? The field site is in the Petrified Forest National Park in northeastern Arizona. And we discovered this site in 2011 after my colleague Robyn Watley. And I started a project to look for some of the earliest mammals. Mammals at that time were not quite mammals the way we would think of them. We're very small. The site itself was discovered by Bill Amarall, a wonderful fossil finder. And we saw him on this little hill. And he said, "I think I've got something good here, huh?" Turned out, he was absolutely right. This assemblage that's preserved in this bonebed has 16 vertebrate taxa that range from things like fresh water sharks and rafened fish to medium-bodied herbivorous reptiles that are armored that are related to living crocodilians. To flying terraces, the new species that we named in this study, to large-bodied apex predators like these rouseukians, so another relative of living crocodilians. So it's this diverse, ecologically complex community of vertebrates, both living in the water and also living around these river channels on the surrounding floodplains. There are big chunks of reworked rock and the bones are fragmentary, and it's all kind of an unsorted and mixed assemblage. The bones are not lying next to each other. You find a jaw here, a piece of the leg bone there. But if you dig down far enough in this quarry, the bones are in very good condition, and there are a lot of very small things as well. So we hit the jackpot in terms of finding the kind of locality that would tell us about the small vertebrates that were living at this time, which we then figured out was about 209 million years ago, but there was no trace of a mammal anywhere. So then that became kind of a puzzle, and also dinosaurs seem to be absent when they should be there. Tell us about the tarisaur you found as part of this assemblage. Why is it a unique specimen? The first one that was found on the land on the land was one of the oldest tarisaur fossils found on earth at 209.2 million years ago. It's also about 5 centimeters long, and it's remarkable because it's preserved in a deposit in a river channel. Almost all early tarisaur fossils are preserved in oceanic or lake sediments, and almost all of them are preserved as these two dimensional slab specimens, so they've been flattened, and so they don't really preserve three dimensional morphology very well. So we were able to use micro CT scanning to basically examine the internal anatomy of this jaw and find things like replacement teeth observe patterns of how the teeth are attached into their sockets, and a lot of this was data that we just simply had never been able to observe before in a early tarisaur. Surprise to find that the teeth showed that the animal had worn off the tips of these sharp little cusps. It says something about what they were eating. They were eating other animals. We assume they were carnivores that were wearing down their teeth. We don't know for sure, but the candidate for something to eat or fish that have very hard and amyloid scales. And our deposit has quite a lot of just single scales from these fish as well. So clear that they were there. What does this tarisaur tell us about the evolution and ecology of tarisaurus? So it's found in equatorial pangea, so rewinding 209 million years ago North America was located much farther south than it is today. So the climate is progressively becoming drier after 215 million years ago. And so this tarisaur is living in this ratifying environment and so it suggests that tarisaur is early in their evolution or able to live not just in maybe wetter climates on the margins of oceans where they're commonly found in Europe at the same time. So it raises the question of when did tarisaur show up in the continental interior of pangea, whether we will find ones that are older is yet to be seen. We say it's a ratifying and that means that probably there were longer dry seasons, but it wasn't entirely a desert. But there was a fluctuation of water and that contributed to this deposit because we think there was a flush flood during one of the periods when it rained and sort of flushed things out in dry channels and reworked the mud and some of the bones but not very much and then deposited them right away. Which you see that happening today in semi-era environments when the rains come. What are the important insights that have come out of studying this community? For the roughly 12 million years preceding the n-triassic extinction which occurs at about 201.5 million years ago, we don't have well preserved diverse vertebrate communities that are precisely dated anywhere on earth. And so this site were able to put together a complete paleo community from the latest triassic interval and we can put a date on it. And that's important because we don't exactly know what happened on land at the n-triassic extinction. Our understanding of this mass extinction is mostly based off of oceanic marine sediments. And the stratigraphic record of sedimentary rocks that could preserve fossils surrounding this extinction event is just really poor globally. And so our study here is describing a fossil site that starts to partially close this major graph preceding the extinction. These organisms were living together in a viable community and what that means today, ecosystem, there are lots of different parts that depend on one another. And so this one was composed of archaic elements and animals that went on and survived through the next 7 million years and into the post n-triassic extinction and became the modern animals of turtles, the frogs and many more. But it's a fascinating window at how you can assemble a community and then maybe put it under stress and later on you see what happened when the extinction occurred and some species survived and others did not. What are the implications of this study for paleontology? Using our excavation methods where we take blocks of the sediment which is very soft and you can't excavate it successfully in the field. You plaster blocks, you bring them back, you have the volunteers and the expert excavators working here under microscopes has allowed us to unveil this community. And other paleontologists are already adopting that as well when they can't get the recovery of fossils from their deposits. I would be really surprised if there are not other late-triassic terraces preserved in these types of river deposits, probably all around the world. But it would take using the methods that we developed to actually recover their extremely delicate fossils to even know they existed there. So I feel like this is a call to arms to start looking for these things. Maybe there aren't such big gaps in the record as we might have thought. If you just see a little bit of tiny bones sticking out of a rock, you can take it to the lab and you can have people try to remove the rock and sometimes that's very difficult. But now you can put the rock into the micro CT scan and if the contrast is enough you can get these little fossils out that way and you don't actually have to physically prepare them. What are the caveats or limitations of the study? We only have three bones that we've confidently identified as parts of the terrace or this lower jaw, tooth and a wing finger. And so that means that most of the anatomy of this animal is unknown. Our artistic reconstructions of this terrace are based off of its closest relatives, species like Udheim, Morphedon from the late-triassic of Italy. Now this is a particular place with a particular set of what we call tephanomic conditions. Tephanomy is how the things get preserved. So you can get carried away thinking, well this is a really good sample of the community that lived there. But it is a very example. It's a preserved sample and there are absences that are puzzling like the dinosaurs, the mammals and some other major groups that are not there. there. So either that's a tephanemic problem of non-preservation or it's a paleo-ecologic problem that they actually weren't there. How do you tell the difference? So that's a problem for the future. Thanks for tuning into science sessions. You can subscribe to science sessions on iTunes, Spotify, or wherever you get your podcasts. If you like this episode, please consider leaving a review and helping us spread the word.