Petrified Forest paleontologists find oldest caecilian fossil

Artistic reconstruction of Funcusvermis gilmorei in the subtropical forest of Petrified Forest National Park around 220 million years ago. (Artwork by Andrey Atuchi/National Park Service)

Artistic reconstruction of Funcusvermis gilmorei in the subtropical forest of Petrified Forest National Park around 220 million years ago. (Artwork by Andrey Atuchi/National Park Service)

PETRIFIED FOREST, Ariz. — Petrified Forest National Park (PEFO) announced the discovery of the world’s oldest caecilian, Funcusvermis gilmorei (pronounced funk-us ver-mis), from the park’s 220 million year old Triassic Chinle Formation last month in the journal Nature by researchers from the National Park Service, Virginia Tech and the University of Washington.

“The discovery of Funcusvermis clears up early amphibian evolution,” Marsh said. “Between salamanders, frogs and caecilians, there has been every hypothesis about how these groups are related. This discovery helps us say: All of our modern amphibians are a monophyletic group. They’re more closely related to each other than they are to any of the other groups of extinct amphibians.”

Previously only 11 fossilized caecilian specimens were known to science, Funcusvermis extended the group’s fossil record by 35 million years through the discovery of 79 individual caecilians and counting as of Feb. 3 according to at Twitter post by PEFO paleontologist and study co-author Adam Marsh.

Caecilians are among the least understood vertebrates because of their fossorial or burrowing lifestyle making them notoriously challenging for biologists to study. They lack arms and legs and are adapted to dig with a robust skull and muscles with reduced eyes which may only be able to distinguish between light and dark.

This new amphibian’s scientific name Funcusvermis gilmorei is inspired by the 1972 funk song “Funky Worm,” by the Ohio Players which was frequently played while the fossils were collected. The researchers wanted to remind people science is fun and to make work an enjoyable experience according to Marsh.

“Funcus" and "vermis," roughly translate to "funky" and "worm," making the the genus Funcusvermis and in honor of Ned Gilmore, the collections manager at the Academy of Natural Sciences at Drexel University in Pennsylvania, the species name is gilmorei.

There are around 200 living species of caecilians who are restricted to the wet and humid equatorial regions— a far cry from modern northern Arizona’s climate. However, this is similar to Arizona around 220 million years ago during the late Triassic when North America was part of the supercontinent Pangea and was located about 10 degrees north of the equator. While that ancient landscape is no more, remnants of it are preserved in the Chinle Formation that makes up PEFO.

For paleontologists finding the often less than 1 cm bones of caecilians is difficult which makes tracing amphibian evolutionary history moreso. But for paleontologists, fossil localities frequently contain entire ancient ecosystems and searching grain by grain of Chinle Formation sediment under the microscope can change our understanding of the evolutionary history of life on Earth.

The announcement builds on the 2019 PEFO discovery of the oldest fossil frogs in North America which, like Funcusvermis, were found by washing and sorting fossiliferous rocks “matrix sorting.” While PEFO does plenty of traditional excavations of fossil localities in the Chinle using hand tools to create field jackets of burlap and plaster around large animal fossils to transport specimens to the lab. Matrix sorting looks for micro-fossils or those specimens that are generally less than a centimeter by soaking sediment in water and than uses screens to pick through sediment.

“It's a less selective and less filtered way of fieldwork,” Marsh said. “We're trying to get a 100 percent collection of a site. In the past maybe you would have one piece of a jaw but we're able to recover more pieces and put them back together to get a more complete picture. Then we can CT, scan them and print them out in a bigger scale and study them in different ways.”

Funcusvermis has implications for understanding how modern ecosystems and our modern animal lineages have evolved according to Marsh who went on to say that. Modern animal groups actually have much deeper roots than we really knew about and are probably coexisting with one another far earlier than we're actually finding in the fossil record until we find places like Thunderstorm Ridge.

The Expansion Lands

Funcusvermis was discovered in 2019 at Thunderstorm Ridge, an active research fossil locality east of Blue Mesa in PEFO’s expansion lands.

That side of PEFO is primarily composed of what was the Paulsell Ranch. In 2004, Congress passed the Petrified Forest Expansion Act authorizing the park to expand by approximately 125,000 acres through willing sellers and a land transfer with the Bureau of Land Management. Several different agreements were made with private landowners and the former Paulsell Ranch was purchased in 2011 with assistance from The Conservation Fund.

NPS policy is to conduct resource surveys when new land is acquired, and from 2016-2018, paleontological surveys were conducted with nearly 300 new fossil localities discovered in the first two years according to Marsh. Among the 2018 finds was Thunderstorm Ridge, named after the park’s previous paleontologist, Bill Parker, who took refuge there when a thunderstorm struck while surveying.

The main indicator for researchers to look through the sediment was the abundance of coprolites or fossilized feces eroding out of the site.

“The University of Oregon recently did a study at PEFO looking to fossils from space via satellite,” Marsh said. “But we can almost find them hillside to hillside by just seeing coprolites pour out. In some of these spots, you can almost predict where some of these micro vertebrate sites are based on how many coprolites are found.”

It’s unclear the association between the abundance of microfossils and coprolites according to Marsh but their main hypothesis is that the abundance of microfossils and coprolites are related because they were both buried in a pretty oxygen poor or oxygen depleted environment. so there wasn't any biotic activity breaking down material.

“The Paulsell Ranch lands are in a checkerboard pattern with State Trust lands—26,000 acres of private (now federal) lands and 23,000 acres of Trust lands alternating square mile by square mile,” according to the Friends of Petrified Forest website.

The adjacent Arizona State Trust Lands haven’t been as robustly investigated as the PEFO expansion areas and require further paleontological inventory based on what has been found on NPS land and how those fossil beds continue across the landscape according to Marsh. However, the Burke Museum, the University of Washington and the University of Texas at Austin have held permits to study the state’s land over the last few decades.

PEFO collected about two tons of sediment from Thunderstorm Ridge and has about 800 pounds left to go through and has found a Funcusvermis jaw about every 32 pounds according to Marsh.

“There’s lots of discoveries from this site incoming,” Marsh said. “We're working on writing up the full assemblage (of Thunderstorm Ridge). Because, it's one of the most diverse micro vertebrate assemblages in the Mesozoic Era and there’s probably at least 60 different taxa in that site and a good percentage of them are either new genera or new species.”

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