Two hundred and thirty million years ago, in what's now Wyoming, the seasons were dramatic. Torrential rain would pelt the region for months on end, and when the mega-monsoon ended, the region became extremely dry. This weather would have been challenging for amphibians that need to keep their skin moist, but one group of salamander-like creatures found a solution, as evidenced by their bizarre fossils. In a new study in the journal Proceedings of the Royal Society B, researchers described a new species of fossil amphibian, preserved in torpedo-shaped burrows where they waited out the dry season.
"Based on how the rocks in the area formed and what they're made of, we can tell that Wyoming experienced some of the most drastic seasonal effects of the mega-monsoon that affected the whole supercontinent of Pangea," says Cal So, the study's lead author and an incoming postdoctoral scientist at the Field Museum in Chicago. "So how did these animals stay moist and prevent themselves from drying out during the hot and dry season that lasted several months? This is the cool thing. We find these fossils inside these cylindrical structures up to 12 inches long, which we've interpreted as burrows."
So, who recently obtained their PhD from George Washington University, first encountered the strange fossil burrows when they were an undergraduate at the University of Wisconsin, working with Research Scientist David Lovelace of the University of Wisconsin Geology Museum.
In 2014, Lovelace was searching for fossils in Wyoming, in an area stewarded by the Bureau of Land Management in a rock layer he would eventually call the Serendipity Beds. "One of my passions is ichnology-- the hidden biodiversity that can be shown through tracks of animals or traces of other living organisms," says Lovelace. He spotted a small cylindrical structure, and several larger ones that looked "like a Pringle can," made of rock. Lovelace recognized the structures as in-filled burrows made by an animal long ago, but a small one stood out. "It was tiny, it was so cute," he says. He collected several of the cylinders for his research.
Back in the lab, Lovelace took a hammer to one of the preserved burrows to see if there were any fossils inside, and he found a tiny, toothy skull. "I saw sharp, pointy teeth, and my first thought was that it was a baby crocodile," Lovelace says. "But when we put it all together and prepared it, we realized it was some sort of amphibian."
Lovelace reached out to Jason Pardo, a postdoctoral researcher at the Field Museum who specializes in fossil amphibians, who created high-resolution CT scans of another of the fossil burrows and revealed a tiny skeleton inside. "At this point, we were like, 'Oh my god, we have something really cool,'" says Lovelace. "I went back to put together the geological story of the site, and then we were just finding these burrows everywhere. We couldn't not find them, the site was ridiculously loaded."
On one of his return trips, he dispatched So, who was then an undergraduate, to collect more of the burrows. Ultimately, the team gathered around 80 fossil burrows, most of which contained skulls and bones of the ancient amphibians. These bones contained clues to the animals' lifestyles. No complete skeletons have been found, but based on the partial remains, they were probably about a foot long. They had tiny, underdeveloped arms, but the researchers think they had another way to dig their burrows.
"Their skulls have kind of a scoop shape, so we think they used the head to scoop their way underground at the bottom of a riverbed and go through a period of having a lower metabolic rate so that they could survive the dry season. That's similar to what some modern-day salamanders and fish do," says So. Essentially, the ancient, aquatic amphibians spent the rainy part of the year swimming in rivers, but when those rivers dried up, they dug head-first into the muddy riverbed. They spent the dry season underground, in a state somewhat similar to hibernation, until the monsoon returned a few months later and the rainwater replenished the rivers. The fossils found by So and Lovelace just happened to be unlucky in that the rivers' paths changed from year to year. The spots where these animals buried themselves were no longer kept moist, so the animals never emerged and instead died in their burrows.
The ancient amphibians lived in what's now the ancestral lands of the Eastern Shoshone people, with whom the researchers have an ongoing collaborative relationship. "Our interest is in education, so we met with the Tribal Historic Preservation Officer for the Eastern Shoshone, and he connected us with the schools," says Lovelace. "It was a great multi-generational collaboration. We invited seventh-grade students from Fort Washakie School, their teachers, and elders into the field with us. The elders told us about their understanding of the rock and their history on the land, and the students got to find burrows and bones."
The middle school students are learning the Shoshone language, and they worked with Elders to create a name for the fossil amphibian in Shoshone: Ninumbeehan dookoodukah. In their paper, the researchers explained, "Ninumbee is the name for the mountain-dwelling Little People who hold an important place in Shoshone culture (among others), -han is the possessive affix indicating an affiliation with the Ninumbee, dookoo means 'flesh' and dukah means 'eater.' Altogether, Ninumbeehan dookoodukah means 'Little People's flesh eater,' honoring the Little People and referencing the sharp teeth of the fossil. Our intent is to pay tribute to the Eastern Shoshone people, their language and the land to which they belong."
"The collaboration between our school district (Fremont County School District # 21) and Dr. Lovelace and his team illustrates reciprocity in action and the long-term, transformational impacts that can occur through authentic relationship building between researchers and communities," says Amanda LeClair-Diaz, Office of Indian Education Coordinator and a co-author of the paper. "This process of scientists, community members, educators, middle school students, and Eastern Shoshone elders coming together to learn about these fossils and choosing a Shoshone name for the fossil, Ninumbeehan dookoodukah, solidifies the intergenerational connection we as Shoshone people have to our homeland and the beings that exist within this environment."
Ninumbeehan offers scientists a tantalizing clue about what life was like in Wyoming 230 million years ago. "Small amphibians are really rare in the Triassic, and we don't know why that is," says Pardo. "We find some big ones, but these small ones are really quite challenging to find."
The newly described amphibians also could shed some light on how modern amphibians might fare in the extreme weather conditions brought on by the climate crisis. "Modern amphibian diversity is under substantial threat, and climate change is a huge part of that," says Pardo. "But the way that Ninumbeehan could slow down its metabolism to wait out the dry weather indicates that some lineages of modern amphibians that have similar seasonal behavior might allow for greater survivorship than some of the models suggest. It's a little glimmer of hope."
