A new study in the field of geosciences has uncovered Triassic fossils that provide insight into the origins of living amphibians. The discovery sheds light on the evolutionary history of these creatures and how they emerged during the Triassic period. Further research into these fossils may give us a better understanding of the early development of amphibians and how they adapted to their environments.
A team of paleontologists has discovered the first ‘unmistakable’ Triassic-era caecilian fossil – the oldest-known caecilian fossils – extending the record of this small, burrowing animal by approximately 35 million years. The discovery also fills an 87-million-year gap in the amphibian-like creature’s known historical fossil record.
The smallest of newly discovered fossils can upend paleontologists’ understanding of our past.
Paleontologists from Virginia Tech and the United States Petrified Forest National Park, among others, have discovered the first “unmistakable” Triassic-era caecilian fossils – the oldest-known caecilian fossils – extending the record of this small, burrowing animal by approximately 35 million years. The discovery also bridges an 87-million-year gap in the amphibian-like creature’s known historical fossil record.
The fossil was first co-discovered by Ben Kligman, a doctoral student in the Department of Geosciences, part of the Virginia Tech College of Science, at Arizona’s Petrified Forest National Park during a dig in 2019. Named by Kligman as Funcusvermis gilmorei, the fossil extends the history of caecilians 35 million years back to Triassic Period, roughly 250 million to 200 million years ago.
Prior to this new study, which was published today in the journal Nature, only 10 fossil caecilian occurrences dating back to the Early Jurassic Period, approximately 183 million years ago, were known. Previous DNA studies, according to Kligman, estimated caecilian evolutionary origins back to the Carboniferous or Permian eras, some 370 million to 270 million years ago, bridging the 87-million-year gap. However, no such fossils were discovered.
The discovery of the oldest caecilian fossils highlights the crucial nature of new fossil evidence. Many of the biggest outstanding questions in paleontology and evolution cannot be resolved without fossils like this.
Kligman
“The discovery of the oldest caecilian fossils highlights the crucial nature of new fossil evidence. Many of the biggest outstanding questions in paleontology and evolution cannot be resolved without fossils like this,” said Kligman, who previously discovered a 220-million-year-old species of cynodont or stem-mammal, a precursor of modern-day mammals. “Fossil caecilians are extraordinarily rare, and they are found accidentally when paleontologists are searching for the fossils of other more common animals. Our discovery of one was totally unexpected, and it transformed the trajectory of my scientific interests.”
Kligman and Petrified Forest National Park student intern Xavier Jenkins, now a Ph.D. student at Idaho State University, discovered the fossils in 2019 while processing fossiliferous sediment from the park’s nicknamed Thunderstorm Ridge using a microscope. Funcusvermis was discovered in a layer of the Chinle Formation dated to approximately 220 million years ago, when Arizona was near the equator in the center of the supercontinent Pangaea, according to Kligman. This region was experiencing a hot, humid climate at the time. Arizona is still hot today, but the humidity is low.
“Seeing the first jaw under the microscope with its distinctive double row of teeth gave me chills,” Kligman said. “We knew it was a caecilian right away, the oldest caecilian fossil ever discovered, and a once-in-a-lifetime find.”
Prior to this discovery, an 87-million-year gap in the fossil record obscured caecilians’ early evolutionary history, sparking a decades-long debate among scientists about caecilians’ relationships to their amphibian relatives, frogs, and salamanders.
“Funcusvermis extends the humid equatorial pattern of occurrence seen in all known fossil and living caecilians, suggesting that the biogeographic history of caecilians has been guided by restriction to these ecological settings, likely due to physiological constraints linked to humidity, and constrained by the drift of continental plates into and out of the humid-equatorial zone after the fragmentation of Pangaea,” Kligman said.
Caecilians are limbless amphibians with cylindrical bodies and a compact, bullet-shaped skull that aids in burrowing underground. Caecilians, which are now only found in South and Central America, Africa, and southern Asia, spend their days burrowing in leaf litter or soil in search of prey such as worms and insects. Scientists have found it difficult to study caecilians due to their underground existence. Modern caecilians, according to Kligman, are “eyeless sock puppets with worm bodies.”
Funcusvermis has skeletal features that are more similar to early frog and salamander fossils, bolstering evidence for a shared origin and close evolutionary relationship between caecilians and these two groups. Funcusvermis also shares skeletal characteristics with an ancient group of amphibians known as dissorophoid temnospondyls by paleontologists. “Unlike living caecilians, Funcusvermis lacks many adaptations associated with underground burrowing, indicating a slower acquisition of features associated with an underground lifestyle in the early stages of caecilian evolution,” Kligman adds.
Name that tune
Now comes the exciting part: The name ‘Funky Worm’ was inspired by the Ohio Players’ 1972 song “Funky Worm” from their album Pleasure, a favorite song of the authors that was frequently played while excavating fossils at Thunderstorm Ridge. ‘Funcus’ is a Latinized form of the English word Funky, which refers to an upbeat, rhythmic style of dance music, whereas’vermis’ is a Latin word for worm. (By the way, it’s a fantastic song. So to speak, an instant earworm.)
The species name, gilmorei, honors Ned Gilmore, the Drexel University collections manager at the Academy of Natural Sciences of Philadelphia. (Kligman is from Philadelphia and worked as an undergraduate student with Gilmore’s herpetology wet collection. “He was an important mentor who helped inspire my interest in fossils and amphibians,” Kligman said.)
Michelle Stocker, an assistant professor in the Virginia Tech Department of Geosciences, and Sterling Nesbitt, an associate professor, are co-authors on the study, as are members of the Fralin Life Sciences Institute’s Global Change Center. Other authors include Adam Marsh, lead paleontologist at Petrified Forest National Park, Matthew Smith, museum curator, William Parker, chief of science and resource management; and Bryan Gee, postdoctoral fellow at the University of Washington’s Burke Museum and Department of Biology.
“As the eponymous song says, it’s the funkiest worm in the world,” Marsh quipped.
Stocker went on to say, “What we collect greatly influences what we can say about which animals were present, how many there were, and how they looked. We would miss out on learning about many important aspects of this Triassic ecosystem if we did not use these methods for fossil collection and analysis. It will be exciting to see what other fossil localities preserve these early lissamphibians now that we have a search image of what bones to look for and how to look for them.”
Nesbitt said finds such as this can reset the game board on paleontology, in the best sense of the phrase. “This find clearly demonstrates that some fossils that you can barely see can greatly change our understanding of entire groups that you can see today,” he said.
