Triassic amphibians had unique adaptations for seasonal estimation

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

Life reconstruction of Ninumbeehan dookoodukah in a palaeoenvironmental reconstruction depicting its life and burrows across seasons: (left) Ninumbeehan dookoodukah resting on the edge of a river with a low water table as the wet season ends; (center) a small community of Ninumbeehan dookoodukah are in their estivation caves at the peak of the dry season; (right) the beginning of the wet season brings rains that trigger a mass emergence of Ninumbeehan dookoodukah from their precious graves. Some individuals expire before the incoming rains, leaving them to be preserved as fossils. Image credit: Gabriel N. Ugueto.

The newly described fossil species, Ninumbeehan dookoodukahlived over 231 million years ago (Early-Late Triassic).

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

The well-preserved skeletal remains of several Ninumbeehan dookoodukah individuals were discovered in association with their aestivation burrows i Formation of Jelm in Fremont County, Wyoming, USA.

“Based on how the rocks in the area were formed and what they’re made of, we can tell that Wyoming experienced some of the most drastic seasonal effects of the megamonsoon that affected the entire supercontinent of Pangea,” said Dr. Cal So, postdoc at the Field Museum.

“So how did these animals stay moist and prevent themselves from drying out during the hot, dry season that lasted several months?”

“This is the cool thing. We’re finding these fossils inside these cylindrical structures up to 30 cm (12 inches) long that we’ve interpreted as caves.”

“We collected about 80 fossil burrows, most of which contained skulls and bones from the ancient amphibians.”

“These bones contained clues to the animals’ lifestyle. No complete skeletons have been found, but based on the partial remains, they were probably around 30 cm long.”

“They had small, underdeveloped arms, but we think they had a different way of digging their burrows.”

“Their skulls have a sort of scoop shape, so we think they used their heads to scoop their way underground at the bottom of a river bed and go through a period of lower metabolism so they could survive the dry season ,” he says. said researcher.

“It’s similar to what some modern 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 headfirst into the muddy riverbed.”

“They spent the dry season underground, in a state somewhat akin to hibernation, until the monsoon returned a few months later and rainwater replenished the rivers.”

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

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

Ninumbeehan dookoodukah could also shed some light on how modern amphibians can manage in the extreme weather conditions that the climate crisis has brought about.

“Modern amphibian diversity is under significant threat, and climate change is a big part of that,” said Dr. Bye.

“But like that Ninumbeehan dookoodukah could slow its metabolism to wait out the dry weather, indicates that some lineages of modern amphibians that have similar seasonal behavior may allow greater survival than some of the models suggest. It is a small 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 saw et al. 2024. Fossil amphibians provide insight into the interplay between monsoons and amphibian evolution in palaeoequatorial centria systems. Proc. R. Soc. B 291 (2033): 20241041; doi: 10.1098/rspb.2024.1041