Triassic Amphibian Had Unique Adaptations for Seasonal Estivation | Sci.News

Paleontologists have described a new species of fossil temnospondyl amphibian from the Triassic Jelm Formation of Wyoming, preserved in torpedo-shaped burrows where they waited out the dry season.

The newly-described fossil species, Ninumbeehan dookoodukah, lived over 231 million years ago (early-Late Triassic epoch).

The ancient creature belongs to Temnospondyli, a diverse order of tetrapods that are often considered primitive amphibians.

The well-preserved skeletal remains of several Ninumbeehan dookoodukah individuals were discovered in association with their estivation burrows in the Jelm Formation in Fremont County, Wyoming, the United States.

“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,” said Dr. Cal So, a postdoctoral researcher at the Field Museum.

“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 30 cm (12 inches) long, which we’ve interpreted as burrows.”

“We 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 30 cm long.”

“They had tiny, underdeveloped arms, but we 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,” the researcher said.

“That’s similar to what some modern-day salamanders and fish do.”

“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.”

Ninumbeehan dookoodukah 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,” said Dr. Jason Pardo, a postdoctoral researcher at the Field Museum.

“We find some big ones, but these small ones are really quite challenging to find.”

Ninumbeehan dookoodukah 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,” Dr. Pardo said.

“But the way that Ninumbeehan dookoodukah 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.”

The discovery of Ninumbeehan dookoodukah is reported in a paper in the journal Proceedings of the Royal Society B.

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Calvin So et al. 2024. Fossil amphibian offers insights into the interplay between monsoons and amphibian evolution in palaeoequatorial Late Triassic systems. Proc. R. Soc. B 291 (2033): 20241041; doi: 10.1098/rspb.2024.1041