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According to scientists, the creature named after the frog Kermit offers clues to the evolution of amphibians

  • Scientists on Thursday described the fossilized skull of a creature called Kermitops gratus that lived in Texas about 270 million years ago.
  • The fossil was collected in 1984 near Lake Kemp in Texas.
  • It is in the extensive collection of the Smithsonian Institution’s National Museum of Natural History in Washington.

There definitely weren’t any Muppets during the Permian period, but there was a Kermit – or at least a precursor to modern amphibians named after the famous frog.

Scientists on Thursday described the fossilized skull of a creature called Kermitops gratus that lived in what is now Texas about 270 million years ago. It belongs to a lineage that is thought to have given rise to the three living branches of amphibians – frogs, salamanders and limbless caecilians.

While only the approximately 3 cm long skull was discovered, the researchers believe that Kermitops had a powerfully built, salamander-like body about 15 to 17 cm long, although salamanders would not evolve for another 100 million years.

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Amphibians are one of the four groups of living terrestrial vertebrates, along with reptiles, birds and mammals. The unique features of the Kermitops skull—a mix of archaic and more advanced features—offer insights into amphibian evolution.

Fossil skull

Shown is a composite image comparing the fossil skull of the Permian-period protoamphibian Kermitops (left) with the skull of a modern frog. (Brittany M. Hance, Smithsonian/Handout via REUTERS)

“Kermitops helps us understand the early history of amphibians by showing that there is no clear trend of gradually becoming more similar to the modern amphibian,” said Calvin So, a paleontology doctoral student at George Washington University and lead author of the study published in the Zoological Journal of the Linnean Society.

The fossil was collected near Lake Kemp in Texas in 1984 and stored in the extensive collection of the Smithsonian Institution’s National Museum of Natural History in Washington, but was not thoroughly studied until recently.

Kermitops had a rounded snout, similar to frogs and salamanders. Its eye sockets preserved lid bones—or eyelid bones—a feature no longer present in today’s amphibians. Its skull is composed of roof-like bones, in contrast to the thin and strut-like bones of modern amphibians.

“The length of the skull in front of the eyes is longer than the length of the skull behind the eyes, which is different from the other fossil amphibians that lived at the same time. We think this may have allowed Kermitops to close its jaws more quickly, allowing it to capture faster insect prey,” So said.

The fossil record of early amphibians and their precursors is patchy, making it difficult to pinpoint the origins of modern amphibians.

“Kermitops, with its unique anatomy, really illustrates the importance of continuing to add new fossil data to understanding this evolutionary problem,” said paleontologist and study co-author Arjan Mann of the National Museum of Natural History.

Kermit the Frog was created in 1955 by the late American puppeteer Jim Henson, and a Kermit puppet made in the 1970s is in the collection of the Smithsonian National Museum of American History as an important cultural object.

Kermitops means “Kermit face” and is a reference to the Muppets’ humorous appearance.

“We thought the eyelid bones gave the fossil a bug-eyed appearance, and combined with a crooked smile created by lightly crushing the fossil during preservation, we really thought it looked like Kermit the Frog,” So said.

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Kermitops belonged to a group called temnospondyls, which arose from fish ancestors a few tens of millions of years after the first land vertebrates evolved. The largest temnospondyls superficially resembled crocodilians, including two that were each about 20 feet long, Prionosuchus and Mastodonsaurus.

Temnospondyls are considered the ancestral lineage of modern amphibians, Mann said.

Kermitops existed about 20 million years before the worst mass extinction in Earth’s history and about 40 million years before the first dinosaurs. It lived alongside other members of the amphibian lineage as well as the formidable sail-backed Dimetrodon, a predator related to the mammalian lineage.

The environment in which Kermitops lived appears to have alternated between warm and wet seasons and hot and dry seasons.

“This environment would be similar to today’s monsoons that occur in the southwestern United States and Southeast Asia,” So said.

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