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Creature named after Kermit the Frog offers clues to amphibian evolution, scientists say


  • 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 was preserved in the extensive collection of the National Museum of Natural History of the Smithsonian Institution in Washington.

There were certainly no muppets during the Permian period, but there was a Kermit – or at least a precursor to modern amphibians named after the famous frog.

Scientists 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 would have given rise to the three living branches of amphibians: frogs, salamanders and limbless caecilians.

Although only the skull – measuring about 1.2 inches long – was discovered, researchers believe that Kermitops had a sturdy salamander-like body, measuring about 6 to 7 inches long, although salamanders would not evolve for about 100 million years.


Amphibians are one of four groups of living terrestrial vertebrates, along with reptiles, birds and mammals. The unique features of Kermitops’ skull – a mix of archaic and more advanced features – provide insight into amphibian evolution.

Fossil skull

A composite image compares the fossil skull of the Permian period proto-amphibian 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 revealing that there is no clear trend to gradually resemble modern amphibians,” said Calvin So, a doctoral student in paleontology at George Washington University and lead author of the study published in the Zoological Journal of the Linnaean Society.

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

Kermitops had rounded snouts, much like frogs and salamanders. Preserved in its eye sockets were the palpebral bones – or eyelid bones – a feature absent in today’s amphibians. Its skull is made of roof-shaped bones, unlike the thin, rack-shaped 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 differs from other fossil amphibians living at the same time. We think this could have allowed Kermitops to close its jaws more quickly,” enabling the capture of fast-moving insect prey,” So said.

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

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

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

Kermitops means “Kermit face”, a nod to the muppet’s humorous look.

“We thought the eyelid bones gave the fossil a bug-eyed appearance, and combined with a lopsided smile produced by a slight crush during preservation of the fossil, we really thought it looked like Kermit the Frog.” , said So.


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

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

Kermitops existed about 20 million years before the worst mass extinction in history. 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 impressive Sailed Dimetrodon, a predator related to the mammalian lineage.

The environment in which Kermitops lived appears to have alternated between hot, humid seasons and hot, arid seasons.

“This environment would be similar to the current monsoons that occur in the southwest United States and Southeast Asia,” So said.


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