Ahvaytum bahndooiveche: North America’s Oldest Dinosaur

The first dinosaur named in 2025 may also be the oldest ever discovered in North America.

Meet Ahvaytum bahndooiveche (pronunciation ‘ah-vay-tum bon-do-ee-vee-chee’), a new genus of Sauropodomorph discovered in the Late Triassic Popo Agie Formation of Wyoming, USA[i]. Translating to ‘long ago dinosaur’ in the Shoshone language, fossils of the tiny meter-long dinosaur were described by paleontologists led by Dr. David Lovelace of the University of Wisconsin-Madison on Tuesday evening. Radiometric dating of the sediments around Ahvaytum have revealed that the dinosaur lived approximately 229 million years ago (MYA), predating any previous dinosaur found on the continent by approximately 6-7 million years. Long ago dinosaur indeed!

First discovered in 2013, the remains of Ahvaytum consist of an ankle and possible femur found in the Garrett’s Surprise Quarry. Though highly fragmentary, the ankle was found to be very similar to those of other early Sauropodomorphs like Eoraptor lunensis from Argentina and Buriolestes schultzi from Brazil. When plotted into a phylogenetic matrix to understand its closest relationships, Ahvaytum was found to be a close cousin of Eoraptor, Buriolestes, and Mbiresaurus from Zimbabwe.

This suggests that early Sauropodomorphs were far more widespread at this point of the Triassic than previously believed. While their fossils are present in 230-million-year-old rocks from Africa, India, and South America – all located in higher latitudes of Pangea’s southern hemisphere – Sauropodomorphs do not appear in the northern hemisphere until approximately 215 MYA. Historically, it has been assumed this disparity was due to widespread geographical barriers present at equatorially latitudes, thus delaying migration and establishment of the family until the later stages of the Triassic.

The presence of Ahvaytum in the central United States brings doubt to this notion. If Sauropodomorphs originated in the south and were limited in their expansion by a desolate equatorial belt, how did one end up in Wyoming, which would have been closer to the equator during the Triassic? One possibility discussed by the authors is that wet conditions persisted in coastal regions of Pangea, thus providing ecological corridors for species looking to migrate between the two hemispheres. The lack of fossils discovered in this area may be due to sampling bias, with few known localities currently known or accessible to paleontologists.

Alternatively, Sauropodomorphs may have dispersed millions of years prior to the existence of Ahvaytum during or shortly after the Carnian Pluvial Episode (CPE). For 2 million years during the Carnian Stage of the Triassic, some 234-232 MYA, arid conditions in Pangea were replaced by perpetually wet and humid weather. Some paleontologists believe the CPE enabled the dinosaur’s takeover of Mesozoic ecosystems, with widespread diversification being observed in the aftermath of the Triassic’s titanic rainstorm[ii]. The presence of Ahvaytum in North America shortly after the CPE may support this notion, with sauropodomorphs and other dinosaurs diversifying rapidly during the event – or shortly before it.

In fact, fossilized dinosaur footprints support the second case being more likely. While dinosauriform body fossils are absent in the northern hemisphere prior to the CPE, their footprints are abundant in places like Poland[iii]. This suggests that early dinosaurs did disperse prior to the CPE, with the conditions of the bizarre weather anomaly accelerating their diversification and evolution.

If this was the case, then why is there a 15-million-year gap between sauropodomorph bones? One possibility discussed by the authors is that the environments in which they lived did not lend themselves well to fossilization. I’ve discussed in previous articles how preservation biases have impacted our knowledge of North American dinosaurs in the Late Cretaceous; was it possible such conditions also occurred in the Triassic? The answer seems quite possible. After all, paleontologists say only 1% of all animals that have ever lived ended up fossilized; the Triassic sauropodomorph fossils could be part of that 99% to never make it past the burial process.

Discovered alongside the Ahvaytum bones were those of a Silesaurid, another early dinosauriform that either represents a cousin to true dinosaurs or an early branch of Ornithischian dinosaurs. Its presence helps corroborate the notion that dinosauriformes diverged around the CPE, as close relatives to the Silesaurid have been found in places like the Ischigualasto Formation of Argentina. The similar composition of communities in Argentina and at Popo Agie provide strong support for connection between north and south Pangea, either through migration along corridors or diversification in earlier stages of the Triassic.

The discovery of Ahvaytum bahndooiveche has provided the oldest concrete evidence of dinosaurs in the northern hemisphere. With its discovery, the timeline of dinosaur body fossils in North America has expanded back by several million years, thus demonstrating that dinosaur diversification across Pangea happened much more rapidly than we previously anticipated. While it would still take time for them to become the dominant terrestrial lifeforms on Earth, genera like Ahvaytum laid the groundwork for their future success in the Mesozoic.

One final note on Ahvaytum is the story behind its name. The lead author of Ahvaytum’s description, Dr. David Lovelace of the University of Wisconsin-Madison, sought the consultation of the Eastern Shoshone tribe for guidance in naming the new dinosaur. Tribal elders, members of the Eastern Shoshone Historical Preservation Office, and the 7^th grade class of the Fort Washakie School worked together to craft the name Ahvaytum bahndooiveche. Some of the Shoshone members who contributed to the study are coauthors on the publication, a rare and awesome distinction.

While it would have been easy for Dr. Lovelace to briefly mention that the fossils were found on ancestral Shoshone land as an acknowledgement in the paper, the emphasis placed into community outreach is nothing short of inspirational. If that isn’t something special, I don’t know what is!

I do not take credit for any images found in this article. Header image comes courtesy of Gabriel Ugueto and the University of Wisconsin-Madison.

Works Cited:

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[i]  Lovelace, D.M., Kufner, A.M., Fitch, A.J., Rogers, K.C., Schmitz, M., Schwartz, D.M., LeClair-Diaz, A., St. Clair, L., Mann, J., Teran, R. 2025. Rethinking dinosaur origins: oldest known equatorial dinosaur-bearing assemblage (mid-late Carnian Popo Agie FM, Wyoming, USA). Zoologocial Journal of the Linnean Society 203. https://doi.org/10.1093/zoolinnean/zlae153

[ii] Benton, M. J., Bernardi, M., & Kinsella, C. (2018). The Carnian Pluvial Episode and the origin of dinosaurs. Journal of the Geological Society, 175(6), 1019–1026. https://doi.org/10.1144/jgs2018-049

[iii] Dinosaurs roamed the northern hemisphere millions of years earlier than previously thought, according to new analysis of the oldest North American fossils. (n.d.). https://news.wisc.edu/dinosaurs-roamed-the-northern-hemisphere-millions-of-years-earlier-than-previously-thought-according-to-new-analysis-of-the-oldest-north-american-fossils/