The earliest dinosaur in North America is a Wyomingite. It’s not big, and there’s not much of it, but it’s hard to overstate the importance of the 230-million-year-old Ahvaytum bahndooiveche.
Paleontologists at the University of Wisconsin-Madison published a paper on Jan. 8 revealing North America’s newest and earliest dinosaur. The chicken-sized, two-legged omnivore was found in the Popo Agie Formation, a Late Triassic rock deposit in west-central Wyoming.
The specimen is far from complete – only two tiny bones from an animal that would’ve only been a foot tall. But they’re definitely from a dinosaur.
“It’s funny to talk about how we’ve got this exciting new dinosaur, and all we have is a tiny ankle bone about the size of our last bone of our pinky finger,” David Lovelace, a paleontologist and lead author of the Ahvaytum paper, told Cowboy State Daily. “It’s small but mighty.”
Definitely Dinosaur
Wyoming is world-renowned for the quality and quantity of fossils preserved in its rocks from the Jurassic and Cretaceous Periods. That’s why Lovelace’s research has focused on the much earlier rocks from the Triassic Period.
“There just hasn’t been a lot of work in Wyoming’s Triassic deposits,” he said. “That’s one of the things that our lab has focused on over the last decade and the reason this dinosaur took over 10 years to publish.”
The tiny fossils of Ahvaytum were found in 2013. The defining bone of this dinosaur, the holotype specimen, is one of the bones of the dinosaur’s left ankle called the astragalus.
A second bone, the top end of a femur, was also identified as belonging to Ahvaytum. Lovelace admits there’s a possibility that the two bones came from two different dinosaurs but are undoubtedly dinosaur fossils.
“The ankle bone and the femur head have diagnostic characteristics that define Dinosauria,” he said. “We’re super lucky to have those two bones in particular because that’s what led us to know we had a dinosaur.”
The shape and structure of the bones are distinctly different from those of the amphibians and other reptiles Lovelace has studied and described from the Popo Agie Formation. They reveal that Ahvaytum walked on two legs, while most of its larger contemporaries were quadrupeds.
Lovelace also said that the shape of the ankle and femur revealed the early dinosaur’s later lineage. Ahvaytum was a saurischian, or lizard-hipped dinosaur, the ancestor of Wyoming’s sauropods, like Brontosaurus and Diplodocus, and theropods, like Tyrannosaurus.
“We believe that it is a sauropodomorph, specifically, like the Eoraptor from Argentina,” he said. “But we’re talking one bone out of hundreds in its skeleton,” he said. “That is certainly up for change as more information is collected or new specimens are found.”
Small But Mighty
There’s not much more than can be said about Ahvaytum from studying the only two bones currently known to exist. However, Lovelace said they make some educated guesses by studying its relatives.
“We can use phylogenetic inference to provide some insights,” he said. “It was likely omnivorous with a mouthful of sharp teeth, which is weird to think about. The ancestors of the giant herbivorous sauropods still had sharp, pointy teeth.”
Lovelace said a look inside the femur determined that the dinosaur was an adult but not fully grown when it died, walked on two legs, and was “almost certainly feathered.”
“We published a paper in 2020 describing the thermal capacity of these animals,” he said. “Based on the metabolism, which is based on the internal structures of the bone, we know that they were warm-blooded and feathered because of the environment. That’s what they needed to live.”
When alive, Ahvaytum would have been about a foot tall and 3 feet long – a chicken with tiny teeth and a long tail. That makes it one of Wyoming’s smallest dinosaurs and possibly the smallest yet found.
It’s also Wyoming’s earliest dinosaur and the Cowboy State’s first Triassic dinosaur identified from skeletal material. Wyoming’s only other Triassic dinosaur, Agialopus, was identified from a single footprint — also found in the Popo Agie Formation — in 1933.
An artist’s rendering of what Ahvytum bahndooiveche may have looked when it lived 230 million years ago in what is now Wyoming. (Illustration by Gabriel Ugueto via University of Wisconsin)Northern Aggression
Beyond its significance as Wyoming’s earliest dinosaur, Ahvaytum is also North America’s earliest-known dinosaur. That makes the importance of this discovery hard to overstate.
During the Late Triassic, the supercontinent of Pangea split into two, forming the continents Laurasia and Gondwana. Modern-day Wyoming was in the middle of Laurasia and was thought to have been entirely devoid of dinosaurs 230 million years ago.
Lovelace explained that while fossils of 230-million-year-old dinosaurs are common in the rocks of the former Gondwana (the modern-day continents of South America, Africa, Australia, and Antarctica), they were previously unknown in the rocks of the former Laurasia.
The lack of these dinosaurs in the Northern Hemisphere led to the hypothesis that dinosaurs originated in Gondwana and that something prevented them from moving to Laurasia.
“The oldest dinosaur specimens are from Argentina, Brazil, and other Southern Hemisphere strata,” he said. “There was almost a 9-to-10-million-year gap between the first occurrence of dinosaurs in the Southern Hemisphere and the Northern Hemisphere. So, there was a hypothesis that climatic barriers prevented the dispersal of dinosaurs into the Northern Hemisphere until much, much later.”
The discovery of Ahvaytum disproves that hypothesis. Dinosaurs were as prevalent and evolved in Laurasia as in Gondwana 230 million years ago.
Lovelace is confident in that assertion thanks to the zircon dating of the rocks of the Popo Agie Formation. High-precision dating using uranium preserved in the rocks reveals that the youngest rocks of the formation are at least 229 million years old.
“Ahvaytum is found below the top of the formation, so that gives us an approximate age of 230 million years,” he said.
That said, Lovelace doesn’t entirely discount the possibility of climatic barriers preventing the spread of dinosaurs in the Late Triassic. At the time, Wyoming was at a latitude between 5 and 10 degrees, just above the equator.
“Maybe they just made it to the equator,” he said, “but the fact is we have a dinosaur at a northern latitude that’s the same age as the dinosaurs from the Southern Hemisphere. That tells us that dinosaurs were prevalent across the globe at that time.”
Beyond A Partnership
Most dinosaur names are derived from Greek and Latin. Ahvaytum is the first dinosaur named in the language of the Eastern Shoshone.
Lovelace said the naming is part of an ongoing relationship between his team at the University of Wisconsin-Madison and the Eastern Shoshone Tribe on the nearby Wind River Reservation. Since the dinosaur was found on the tribe’s ancestral land, the paleontological team wanted to honor that and reflect that in its scientific name.
“Traditionally, it was purely white European males doing all the science,” he said. “Researchers are starting to open up to the idea of representing the cultures and communities of the areas where they’re working in the taxa they’re describing.”
Eastern Shoshone tribal elders and middle school students helped Lovelace’s team name their important discovery. Ahvaytum bahndooiveche roughly translates to “long ago dinosaur.”
Several new species recently discovered in the Popo Agie Formation have names derived from the Eastern Shoshone language. Lovelace regularly invites elders and students to his ongoing excavations during the summer and learns from their cultural traditions.
“We wanted to go a step beyond and build a partnership that will last for years and years,” he said. “As Western scientists, we learned how we can approach the land with more respect from the perspectives of the native traditions. It’s been very special for us.”
Two members of a University of Wisconsin field crew work at a site in Wyoming where fossils of a 230 million-year-old dinosaur were found. (Photo by David Lovelace, University of Wisconsin)Piecing Together A Paleoenvironment
Work is ongoing in Wyoming’s Popo Agie Formation. Lovelace said they’re looking for more fossils from Ahvaytum, but there’s a menagerie of new Late Triassic animals waiting to be described and named.
“We have a couple of fantastic new sites that we are excavating that definitely have new taxa,” he said. “I don’t know if we have more dinosaurs, but I would not be shocked that we’ll find more.”
During the Late Triassic, the Popo Agie Formation would have resembled the coastal plains of modern-day Texas. Ahvaytum would have scurried through the underbrush, avoiding the jaws of much larger reptiles like 17-foot-long Heptasuchus, crocodile-like phytosaurs, and four-foot-long burrowing amphibians.
In addition to being mostly overlooked, past paleontologists had a “collections bias” when working in the Popo Agie Formation. Large fossils that were easier to find, identify, and excavate were prioritized over fragmentary specimens.
Lovelace and his team are examining every fossil they find as they slowly resurrect Wyoming as it was in the Late Triassic. In the same paper, the team described a previously unknown silesaurid, another tiny reptile closely related but not completely a dinosaur.
Ahvaytum shows how significant a tiny bone can be.
“It’s a pretty paltry specimen, but it’s a dinosaur,” he said. “It’s less about this particular taxon as much as it is that we have a dinosaur, at this place and time, that has changed our perspectives on dinosaur evolution.”
Andrew Rossi can be reached at [email protected].
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Publish date : 2025-01-11 04:12:00
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