Enormous, Crocodile-Sized Amphibians Mysteriously Died Together in Wyoming 230 Million Years AgoPaleontologists found a group of four-legged Triassic creatures preserved in the same bone bedbut they dont know what killed the animals A skull of the Triassic amphibian Buettnererpeton bakerigets uncovered for the first time in 230 million years. Researchers found it in a cache of skeletons that were well-preserved and appear to be relatively undisturbed over time. Dave LovelaceRoughly 230 million years ago, a group of alligator-sized amphibians convened on a floodplain in what is now west-central Wyoming. For some mysterious reason, the creatures all died around the same time.Sediment slowly covered their bodies. For millennia, their fossilized bones remained hidden inside layers of rockuntil now.Paleontologists recently unearthed the creatures well-preserved skeletons and are now trying to piece together what killed them, according to a new paper published April 2 in the journal PLOS One. The fossil cache may also offer new insights into the lives of these long-extinct amphibians, called Buettnererpeton bakeri.B. bakeri was a primitive, four-legged amphibian that lived in North America during the Triassic Period, which spanned between 201 million and 252 million years ago. The species belonged to a group of amphibians known as metoposaurid temnospondyls, which were the ancestors of todays salamanders, frogs and toads.Researchers think B. bakeri lived in freshwater lakes, ponds and rivers, where it hunted fish and amphibiansand anything else tasty that came along. But they dont know much about the creatures lifestyle and habits, because they havent found very many B. bakeri fossils.The recent discovery might change that: The bone bed unearthed at a site called Nobby Knob in Dubois, Wyoming, more than doubles the total number of known B. bakeri specimens. While digging through rocks dating to 230 million years ago, paleontologists found the fossilized remains of at least 19 individuals, writes Live Sciences Skyler Ware. The Wyoming cache more than doubles the number of known B. bakeri specimens. Kufner et al., PLOS One, 2025The bones are relatively undisturbed and seem to be arranged in much the same way they were positioned when the animals died. This suggests the amphibians perished in calm waters and were gently buried by layers of fine sediment over time. Even very delicate parts of the creatures skeletons were preserved, according to a statement from the journal. Paleontologists also found fossilized poop, plants and bivalve mollusks at the site.There are some articulated bones that are nearly absent in other metoposaurid bone beds in North America, and completely unknown for Buettnererpeton, study co-authors Dave Lovelaceand Aaron Kufner, who are both geoscientists at the University of Wisconsin-Madison, tell Popular Sciences Andrew Paul.Since the bones dont appear to have been moved by strong currents, researchers suspect the creatures died around the same time and in the same placeleaving behind something of a paleontological crime scene, as Paul Smaglik writes for Discover magazine.This assemblage is a snapshot of a single population, rather than an accumulation over time, Kufner says in the statement.But what were they all doing together? And what caused the mass die-off? One possible explanation is that the animals got stuck when nearby waterways dried up during a drought. They may have gathered to breed.For now, at least, their deaths remain an unsolved mystery.More broadly, scientists dont know whether die-offs like this one were common for the large Triassic amphibians, because most bone beds discovered so far contain remains that were transported there by flowing water. Its possible the B. bakeri mass mortality event was a rare fluke.Scientists want to explore these and other questions by conducting future research. By studying the Wyoming fossils further, they also hope to learn even more about B. bakeris biology, as well as the Triassic ecosystems in which they lived.Get the latest stories in your inbox every weekday.