Dozens of amphibians perished together on an ancient floodplain around 230 million years ago, according to a study published April 2, 2025 in the open-access journal PLOS One by Aaron M. Kufner of the University of Wisconsin-Madison, U.S., and colleagues.
Early in the Age of Dinosaurs, alligator-sized amphibians called metoposaurid temnospondyls were common in freshwater habitats. Several fossil sites contain large concentrations of temnospondyls buried together, but determining how these bonebeds formed is often difficult due to a lack of context or detailed examination.
In this study, Kufner and colleagues perform an in-depth assessment of a site called Nobby Knob in Dubois, Wyoming, where fossil remains of a temnospondyl called Buettnererpeton bakeri were found in rocks dating to roughly 230 million years ago. 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. The authors conclude that these animals may have concentrated in this area as a breeding colony or because of restricted waterways due to drought and were ultimately buried together where they died.
This assemblage represents more than of half of the known fossils of Buettnererpeton, providing an excellent opportunity for future study of the species. Whether or not this kind of die-off was common among temnospondyls is difficult to assess since few other sites have received this level of detailed examination and there is limited data regarding how temnospondyl burial varies with different environments. The authors suggest these as directions for future research.
"This assemblage is a snapshot of a single population rather than an accumulation over time" said Kufner, "that more than doubles the number of known Buettnererpeton bakeri individuals." Whether or not this kind of die-off was common among temnospondyls is difficult to assess considering most bonebeds of this group represent accumulations that were transported from the site of death. Few other metoposaurid sites have received this level of detailed examination highlighting the importance of mapping and systematic data collection during excavation and preparation of mass mortality beds. The Nobby Knob fossil assemblage provides an excellent opportunity for future research into Late Triassic ecosystems and metoposaurid biology.
In your coverage, please use this URL to provide access to the freely available article in PLOS One: https://plos.io/4bYbCNP
Citation: Kufner AM, Deckman ME, Miller HR, So C, Price BR, Lovelace DM (2025) A new metoposaurid (Temnospondyli) bonebed from the lower Popo Agie Formation (Carnian, Triassic) and an assessment of skeletal sorting. PLoS ONE 20(4): e0317325. https://doi.org/10.1371/journal.pone.0317325
Author countries: U.S.
Funding: A David B. Jones Foundation grant awarded to DML helped fund the excavation of this material. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
