A new discovery of the earliest dinosaur relative has challenged scientists’ previous theories on their evolution and fills in the missing evolutionary link.

In the paper published Wednesday in the Nature journal, researchers describe a four-legged lizard-like carnivore called Teleocrater rhadinus that would have been between six and 10 feet long.

"The discovery of such an important new species is a once-in-a-lifetime discovery," said lead author Sterling Nesbitt of Virginia Polytechnic Institute and State University in a statement. "Teleocrater fundamentally changes our ideas about the earliest history of dinosaur relatives."

Dinosaurs, as a species, fall under the archosaurs category, which also includes birds, flying reptiles and crocodilians.

Around 250 million years ago the group split in two: the bird-like group, which would evolve into dinosaurs, birds and flying reptiles, and the crocodile-like group, which has crocodiles and alligators.

The newly-discovered Teleocrater is the earliest member of the bird-like side of the family but bears little resemblance to the winged creatures.

As The Field Museum’s associate curator of fossil mammals and paper author Ken Angielczyk explained: “Teleocrater has unexpectedly crocodile-like features."

The crocodilian-like features give scientists a better insight into how dinosaur-like features evolved.

Scientists previously thought that the early relatives of the dinosaurs were small and “very-dinosaur-like” with their features evolving rapidly after breaking away from the crocodile-like side.

“However, Teleocrater shows us that bird-line archosaurs initially inherited many crocodile-like features from the common ancestor of all archosaurs, and that the 'typical' bird-line features evolved in a step-wise fashion over a longer period of time,” said Angielczyk. “[It] is a missing link between dinosaurs and the common ancestor they share with crocodiles."

And the Teleocrater isn’t only filling in a gap in evolutionary history, but it’s also the missing piece to a lengthy academic investigation.

While it is the first time the fossil is being named, it was actually first identified by a British paleontologist named Alan Charig in the 1950s, explained Angielczyk.

"In his thesis, Charig informally identified fossils of an early lizard-like animal that he called Teleocrater, but the understanding of dinosaur evolution at the time was such that he didn't recognize the connection with dinosaurs," he said.

The Teleocrater remained largely a mystery until the researchers discovered more fossils during a dig in Tanzania in 2015.

"We found fossils that we thought might be from Teleocrater, but it wasn't until we were back in the lab that we realized we'd found something really amazing," said Angielczyk.