Fossilized babies of ancient crocodile-like predators have led to a monumental change in understanding of how animals first adapted to life on land. Young fossilized tetrapods show that the common ancestors of amphibians, reptiles, and mammals didn’t evolve from species with amphibian-like tadpoles after all, say scientists.
Challenging Previous Theories
Researchers have long believed that the earliest of the occasional-land-dwellers were like modern amphibians, in that they hatched from eggs, underwent a tadpole phase, and then transformed into their adult bodies. However, American scientists have now discovered fossilized baby early tetrapods, which skipped the tadpole metamorphosis they had expected to see.
The research made use of dozens of fossils discovered at the Mazon Creek fossil deposit in Illinois. The team explained that the fossils represent the evolutionary transition between fish and four-legged animals, or tetrapods, but two “centerpiece” fossils are babies of an animal called an embolomere. Embolomeres were crocodile-like early tetrapods that were among the top predators in rivers, lakes, and swamps from 350 to 280 million years ago.
A New Understanding of Early Tetrapods
Study co-lead author Dr. Jason Pardo, of the Field Museum in Chicago, said: “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. And our study shows that this basic underlying premise, that the first four-legged vertebrates grew up like amphibians, is wrong.”
The discovery, which rewrites decades of scientific understanding of early tetrapod evolution, wouldn’t have been possible without the collaboration of many people. Dr. Arjan Mann, the Field Museum’s assistant curator of early tetrapods, noted that this is a monumental discovery, and it could not have happened without citizen science.
Original reporting: KTBS 3 (Shreveport) — read the source article.
