The earliest known relatives of dinosaurs were the size of a house cat, walked on four legs and left footprints in the quarries in Poland.

The earliest known relatives of dinosaurs were the size of a house cat, walked on four legs and left footprints in the quarries in Poland.

The tracks, described in a report published Wednesday by the journal Proceedings of the Royal Society B,push back the first appearance of this dinosaur lineage to about 250 million years ago.

“They are the oldest fossils of the dinosaur lineage of any type anywhere in the world,” said Stephen Brusatte, a graduate student at Columbia University and lead author of the journal article.

The findings indicate that dinosaurs, which died out in a meteor impact 65 million years ago, originally arose to fill ecological niches opened by an earlier, even greater mass extinction.

“It’s definitely exciting,” said Sterling Nesbitt, a researcher at the Burke Museum at theUniversity of Washington. Dr. Nesbitt said that it was often hard to draw convincing conclusions about animals just from their footprints, but that Mr. Brusatte and his colleagues “put the best argument that anyone has ever put forth about early dinosaur tracks.” He added, “And I think they’re right.”

So far, no dinosaur bones have been found in the rocks, but “the possibilities are really exciting,” Mr. Brusatte said.

The earliest known bone fossils of an animal that fulfilled all of the criteria to be designated a true dinosaur date from about 230 million years ago. But dinosaurs were preceded by ancestors, including the ones that left the Polish footprints, that had similar characteristics and behavior.

“Anatomically, for all intents and purposes, it was a dinosaur,” Mr. Brusatte said. “If you saw this thing, you would call it a dinosaur.”

The dinosaur relatives were far less imposing than tyrannosaurs, triceratops and sauropods. But the dinosaurlike animals left distinctive, albeit small, dinosaurlike prints — three prominent middle digits bunched together — in the muddy plains. The animals had an unusual gait. As they walked, the back feet stepped in front of the shorter front legs.

For these earlier dinosaur cousins, scientists had previously dug up bones dating from 242 million years ago and had found footprints from about 247 million years ago.

The new footprints, uncovered over the past decade by Grzegorz Niedzwiedzki of the University of Warsaw at three quarries in the Holy Cross Mountains of central Poland, push back the lineage to within a couple of million years of the Permian-Triassic boundary, the largest extinction in Earth’s history.

“In geological terms, we now have the dinosaur lineage a blink of an eye after this extinction,” Mr. Brusatte said.

At the two older sites, evidence indicated that the dinosaur relatives all walked on four legs. But at a third site, dated at 246 million years ago, it appears the animals diversified to include larger ones that walked on two legs.

Nonetheless, they were all rare. Only 2 percent to 3 percent of the footprints at the sites were left by the dinosaur cousins, which were far outnumbered by lizards, amphibians and crocodilian reptiles. Only after another extinction 200 million years ago, which largely cleared out the crocodilians, did the age of dinosaurs begin.


A version of this article appeared in print on October 7, 2010, on page