Baby crocodile-like fossils just blew up a long-held evolution theory

[rael science]

---

The Raelian Movement

for those who are not afraid of the future : http://www.rael.org

---

Get Rael-Science on Facebook: http://www.facebook.com/raelscience
Get Rael-Science on Twitter: https://twitter.com/rael_science

---

Source : https://www.popsci.com/environment/first-land-animal-not-amphibians/

 

 

 

 

 

Baby crocodile-like fossils just blew up a long-held evolution theory

Turns out, the first animals to walk on land weren't amphibians..

Sarah Durn

Published   Jun 18, 2026 2:00 PM EDT

An illustration shows prehistoric baby crocodile-like animal known as an embolomere swimming with their mother in the background. Image:   

Sorry, class. Your high school science teacher was wrong. Now, before you fire off an angry email, take a deep breath. They may have technically been wrong, but it’s not their fault. New evidence published today in the journal Science upends decades of evolutionary theory about when animals first walked on land. The new findings suggest these first animals were not, as you might have learned in biology class, anything like modern amphibians. In fact, some of the first animals to step out of the primeval sea were far more like ancient crocodiles. 

“When a lot of us were in high school, we were taught this simplified story of evolution: that some fish evolved into amphibians, and some of those amphibians evolved into reptiles, and some of those reptiles evolved into mammals,” Jason Pardo, a research associate at the Field Museum and the study’s co-lead author, said in a statement. “And our study shows that this basic underlying premise, that the first four-legged vertebrates grew up like amphibians, is wrong,” says Pardo.

So if this new research blows up such a long held theory, what really happened? How did some of our oldest ancestors make the first step onto land some 350 million years ago?

An fossil goldmine just outside Chicago

This particular story begins at a world famous fossil site called Mazon Creek about 70 miles southwest of Chicago, Illinois. The site was discovered in the 1840s, and has been a goldmine for researchers ever since.

“Mazon Creek fossils are time capsules that capture the impossible,” added Arjan Mann, the Field Museum’s Assistant Curator of Early Tetrapods and the study’s other co-lead author. 

“It’s an hour’s drive southwest of Chicago, and it’s one of the best fossil sites in the world, especially for soft tissues and delicate little fossils.”

In their study, Mann and Pardo looked at dozens of Mazon Creek fossils, but the two “centerpiece” fossils were baby animals known as embolomeres. 

Embolomeres looked a bit like modern crocodiles. For millions of years between 350 and 280 million years ago (about 30 million years before the first dinosaurs), these croc-like animals ruled the rivers, swamps, and lakes of the ancient world. Adults could grow over 10-feet-long, but the specimens that Mann and Pardo studied were only a couple of inches long. 

 

I first saw the baby embolomere fossil about 10 years ago, when I was working on my PhD,” said Mann. “It’s in the collections at the Field Museum, and the curator of tetrapods at the time, John Bolt, pulled it out of a drawer and showed it to me when I was visiting. At the time, it hadn’t yet been identified as an embolomere, but I was really drawn to it, and John loaned me the fossil to study.”

Solving the fossil puzzle

At the time, Mann and Pardo were both PhD students in Canada. The pair often spent time trying to decipher the strange fossil. “We had so many conversations over the past decade about what the heck this thing was,” Mann said. “Every night, we’d go back and forth saying, what’s this feature? What could this thing be

 

Eventually, the Canadian Museum of Nature in Ottawa, Canada, confirmed that the fossil was a baby embolomere using electron microscopy. But that only presented more questions because the fossil didn’t show any classic amphibian tadpole traits.

 

While the tiny fossils didn’t have limbs (those would develop as they grew), they also didn’t have external gills. And without gills, it became clear to Mann and Pardo that these baby embolomeres wouldn’t have gone through a classic amphibian metamorphosis from tadpole to adult.

 

“We looked at a number of different species that represent different lineages in the transition from fish to tetrapods [the branch of the fish family that developed legs and crawled onto land], and what we found is that none of them have anything that looks remotely like a tadpole. And if you don’t have a tadpole, then you don’t have a metamorphosis,” said Pardo. “These early tetrapods’ life cycles are more like ours, or like those of fish, than they are like amphibians.”

 

And just like that the theory that the first land-going animals were amphibians evaporates. “That story doesn’t work anymore,” said Pardo. “It’s dust in the wind.”

 

But what really happened then? As often happens in science, with every answer comes more questions.

 

 

Illustration showing a baby embolomere, with an adult in the background. Image: Gabriel Ugueto

 

Sarah Durn

Associate Editor

Sarah Durn runs PopSci‘s ‘Ask Us Anything‘ series and hosts the ‘Ask Us Anything’ podcast. Sarah also launched two new history series at PopSci, ‘That Time When‘ and ‘The History of Every Thing.’ She is the bestselling author of The Beginner’s Guide to Alchemy, and her work has appeared in The New York Times, National Geographic, Smithsonian, WIRED, among others. Previously, Sarah worked on staff as a writer and editor at Atlas Obscura.