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On Scotland's Isle of Skye, scientists have identified two areas with evidence of ancient life forms.
Researchers believe the markings are, in fact, footprints from dinosaurs that lived 170 million years ago. They say the prints date to the middle of the Jurassic Period, a time from which few dinosaur fossils have been recovered.
Researchers reported this month on their study of about 50 fossilized footprints at the two sites. The markings are just a few hundred meters apart from each other. They are said to show dinosaurs walking in different directions.
At least three kinds of dinosaurs left the footprints.
Steve Brusatte, the leader of the research team, is a paleontologist with the University of Edinburgh.
"The tracks are located on flat rocky surfaces near the beach, so they are only exposed at low tide," he said. "The tide laps across them, back and forth, every day."
One set of markings came from a two-legged, meat-eating dinosaur that researchers say was about the size of a car. They say its footprints have three toes. The creature, with sharp claws, appears to be from a group of dinosaurs called theropods.
Bigger, three-toed footprints came from large-bodied, two-legged plant-eaters called ornithopods or perhaps, the researchers say, a large theropod. All of these prints had worn-down toes, not sharp edges.
The researchers are especially interested in markings left by another creature: an early member of a group of heavily built, four-legged plant-eaters called stegosaurs.
The footprints represent some of the oldest evidence anywhere of a stegosaur, notes Paige dePolo, a doctoral student at the University of Edinburgh.
DePolo was the lead writer of a report on the study. The findings were published in the journal PLOS ONE.
The most famous member of the stegosaurs was Stegosaurus, which lived late in the Jurassic Period. It had large, bony protective plates around the neck and back - and a large spiked tail, too.
Brusatte was careful to note that the researchers still have a lot of unanswered questions about this creature.
"I suspect this stegosaur was about the size of a cow, which is fairly small for a stegosaur. Whether that's because it's a primitive, smaller species or a juvenile of a bigger species, we're not sure," he said.
The researchers noted that the findings were an important window into the many kinds of dinosaurs on the Isle of Skye.
"Skye has emerged as one of the most important windows into Jurassic dinosaur evolution. We know that dinosaurs were diversifying with a frenzy in the Middle Jurassic, but there are few fossil sites of this age anywhere in the world," Brusatte added.
I'm John Russell.
Will Dunham reported on this story for Reuters. John Russell adapted the report for VOA Learning English. George Grow was the editor.
