October 18, 2007—Newly found fossilized footprints show that reptiles walked the Earth a bit earlier than scientists believed.
An unknown animal created the fossilized prints seen above while strolling along the muddy bottom of a nearly dry riverbed.
The tracks were found in the same region of New Brunswick, Canada, where the oldest-known reptile skeletons were unearthed 150 years ago.
But the ancient footprints are preserved in sediments that lay more than half a mile (nearly a kilometer) deeper than those 315-million-year-old bones—which suggests they were made by an animal that lived one to three million years earlier.
Howard Falcon-Lang from the U.K.'s University of Bristol said it was lucky that his team even found the fossil. The slab of rock had fallen from a remote stretch of sea cliffs, and a low sun shining across the surface cast revealing shadows.
"This kind of work was a bit like a crime scene investigation," Falcon-Lang added. "We had the footprints, and we needed to know what kind of [animal] left the prints behind."
Distinctive digits told the tale. Because the tracks showed five fingers and some evidence of scales, they had to have been made by a reptile, the team reports in a recent issue of the Journal of the Geological Society of London.
The find helps fill a critical gap between the oldest reptile fossils and those of an amphibian ancestor that lived some 20 million years earlier, Falcon-Lang said.
The prints also seem to confirm theories of how reptiles evolved to live and breed on land, eventually inhabiting terrestrial ecosystems that amphibians could not.
"The expectation we have is that reptiles, once they evolved, would be moving into dry environments," Falcon-Lang said. "That's exactly what these tracks show us."
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