A paleontologist from the Field Museum of Natural History has unveiled new insights into the fossilized remains of a baby embolomere, a crocodile-like predator that inhabited ancient rivers and swamps between 350 million and 280 million years ago. Contrary to previous beliefs, these early vertebrates did not resemble tadpoles during their infancy.
New fossil evidence suggests that embolomeres did not undergo the same metamorphosis as modern amphibians, contradicting the notion that amphibians, reptiles, and mammals evolved from tadpole-like ancestors. Image credit: Berit Godling.
“Many of us learned a simplified version of evolution in high school: that fish evolved into amphibians, which then led to reptiles, and finally to mammals,” said Jason Pardo, a paleontologist at the Field Museum.
“Our research indicates that this fundamental premise—that the first four-legged vertebrates developed like amphibians—is incorrect.”
In their recent study, Dr. Pardo and colleague Dr. Arjan Mann analyzed well-preserved fossil quadrupeds from Mason Creek Lagerstätte, Illinois, known for its exceptional soft tissue specimens.
“Mason Creek is one of the world’s best fossil sites for soft tissue and delicate small fossils,” remarked Dr. Mann.
“The fossils from Mason Creek serve as a time capsule, allowing us to gain insights that were previously thought impossible.”
Embolomeres could grow over 3 meters (10 feet) as adults and were fearsome apex predators in ancient rivers, lakes, and swamps from 350 million years ago (Carboniferous period) to 280 million years ago (Permian period).
The Mason Creek specimen offers a striking contrast; though the baby is just a few centimeters long, it provides enough evidence to challenge century-old scientific assumptions.
Notably, researchers observed that embolomere offspring lacked crucial characteristics associated with amphibian tadpoles, such as external frilled gills.
No evidence of true metamorphosis was found in these early tetrapods, despite the major changes that occur during the larval stage in modern amphibians.
Instead, the life cycles of these initial tetrapods appear to resemble those of humans or fish more than they do those of amphibians.
“We examined a range of species representing various lineages throughout the fish-to-tetrapod transition and found no evidence resembling a tadpole,” Pardo stated.
“If there are no tadpoles, then metamorphosis cannot exist.”
“If creatures like embolomeres did not display tadpole morphology or undergo true amphibian metamorphosis, then the widely accepted theory that reptiles and mammals evolved from amphibian-like ancestors must be reconsidered.”
“The narrative that metamorphosis facilitated the transition of animals from water to land is no longer valid. It’s become obsolete.”
For further details, refer to the findings published in Science.
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Jason D. Pardo & Arjan Mann. 2026. Direct development of stalk tetrapods through the fin-to-limb transition. Science 392 (6804): 1292-1296; doi: 10.1126/science.aeb7635
Source: www.sci.news
