Fossil Graveyard of Giant Amphibians Found in Wyoming

As big as alligators,
these creatures died
suddenly in a floodplain

Dozens of large soft-bodied tetrapods, thought to be “primitive amphibians,” have been found in a fossil graveyard in Wyoming. The press release says,

Dozens of amphibians perished together on an ancient floodplain around 230 million years ago, according to a study published in the open-access journal PLOS One by Aaron M. Kufner of the University of Wisconsin-Madison, U.S., and colleagues.

A skull of Buettnererpeton bakeri alleged to be 230 million years old. The specimen was uncovered in the fossil preparation lab at the University of Wisconsin Geology Museum. Credit: Dave Lovelace, CC-BY 4.0 (creativecommons.org/licenses/by/4.0/).

Ancient amphibians as big as alligators died in mass mortality event in Triassic Wyoming (Phys.org, 2 April 2025). How did dozens of large tetrapods die together? The press release tries to say they were somehow trapped by restricted waterways in a drought when suddenly calm water rose and buried them. That sounds like a highly unusual event.

Fine-grained ancient soils and finely layered sediments indicate that these fossils were buried in a floodplain setting. Unlike similar sites, the water was evidently very calm, since even very delicate parts of the skeletons are preserved intact, and the bones aren’t arranged in any pattern that would suggest strong currents.

Why didn’t amphibians just float and rise to the surface then? And why were so many individuals crammed into the same area? And how could delicate parts of skeletons endure 230 million years? If this were a seasonal event, one would think there would be millions of fossil bonebeds stacked on top of each other in the strata. Why only one?

Figuring out what happened at this spot in the Popo Agie Formation in Fremont County, Wyoming (east of the Wind River Mountains) is reserved for “future research,” the press release says.

A new metoposaurid (Temnospondyli) bonebed from the lower Popo Agie Formation (Carnian, Triassic) and an assessment of skeletal sorting (Kufner et al., PLoS One, 2 April 2025).

Fossils of metoposaurid stereospondyls, thought to be primitive amphibians, are found on every continent. Portions of this paper indicate that the hypothesis that these creatures died in place in calm water is not certain. At least one of the skeletons still had dental plates intact presumably when buried with the gums undisturbed.

Considering the inferred seasonality during Camp Springs deposition, the specimen was likely a desiccated and fragmented carcass. Desiccation or draping of the bone-bearing palatal integument would have allowed for the retention of the denticulate plates leading up to final deposition where these diminutive elements were ultimately preserved in place within the interpterygoid vacuity…. Along with our observations of matrix-supported clasts associated with EP, these data do not exclude the possibility of a debris flow-hosted bonebed. However, in the absence of a quarry map and other firsthand sedimentological and stratigraphic data, these observations remain inconclusive at this time.

Indeed, evidence leads the authors to propose a debris flow from a flash flood:

With the caveat that we lack detailed field observations of our own, we would like to point out that these matrix-supported clasts appear to be more consistent with debris (or possibly hyperconcentrated) flows than the more typical clast-supported conglomerates of braided streams they were inferred to represent. The matrix-supported “conglomeratic” deposits within the Camp Springs Conglomerate may be better explained by debris flow deposition which can follow local topography, occur both subaerially and subaqueously, and travel over short distances and low gradients. Additionally, debris flows would explain the unusual deposits within the Camp Springs Conglomerate (=Santa Rosa Sandstone; or the Tecolotito Member of the Santa Rosa Formation) with large clasts supported in a sandy matrix (fig 2.10d: [70]). Entrainment in a debris flow during a flash-flooding event could explain the lack of abrasion and the presence of small (early dispersal; Voorhies Group I) and large (late dispersal; Voorhies Group III) elements in what has been previously described as high-energy conglomerates of a braided river system.

Clasts are pieces of rock embedded in a deposit from other locations. Finding “large clasts” within the deposit suggests a catastrophic, sudden mass burial event. Bivalve fossils were also found at the site, along with “abundant fragments of weathered petrified wood littering the surrounding area.”

Uniquely among metoposaurid bonebeds, the NK locality preserves articulated and disarticulated denticulate palatal plates (Figs 5E–G). Denticulate plates were embedded in the soft tissue of the palate in life and have been reported from other metoposaurid assemblages but have not been found in articulation within the palate. Disarticulated palatal plates have only been found underneath skulls, but articulated plates have been found in skulls with the palate facing up.

The bonebed site, which they call Nobby Knob (NK), does not seem to fit the geological consensus view of a relatively calm lacustrine environment. They admit that whatever happened is “a mass mortality event of unknown cause.”

Skeleton of Metoposaurus diagnosticus krasiejowensi in the Krasiejów museum in Poland. Credit: Shalom – Own work, Creative Commons

Update: Our report coincided in time with one on Live Science: “Triassic amphibians the size of alligators perished in mass die-off in Wyoming, puzzling ‘bone bed’ reveals.” What does their reporter Skyler Ware say about it?

Because the closely grouped bones weren’t carried to the site by currents, the researchers suspect the animals perished around the same time. They may have been part of a breeding colony or died because they were somehow prevented from leaving a drying body of water they needed to survive, the team suggested. It’s still unclear whether mass metoposaurid die-offs like the one at Nobby Knob were common during the Triassic or whether the site represents an isolated event.

But what does she know? The paper indicates that a debris flow could have been responsible, which involves transport by currents. “It could have been common, or it could have been an isolated event.” This is the kind of “understanding” one gives when stuck in the consensus box. It requires raising the perhapsimaybecouldness index very high.

This looks like an exciting site for researchers willing to think outside the moyboy consensus to investigate. Dozens of alligator-sized amphibians buried together with bivalves and petrified wood? Soft tissue impressions preserved for 230 million years? How could that happen? Creationists and flood geologists should study this site and provide more reasonable alternatives to the view that this was the result of ordinary seasonal processes.