(Read: "Dinosaur Tracks Shed Light on Sauropod Evolution" [May 30, 2002].)
Martin Lockley, curator and director of the University of Colorado, Denver's Fossil Footprint Collection, was also not involved with the research.
"Tracks are a sort of snapshot—almost like a movie of a living animal—whereas bones tell you about the dead ones," Lockley said.
The find may also "spark some ecological debate," Lockley said, since "there's conventional wisdom that the two types of herbivorous dinosaurs—the ornithopods and sauropods—do not commonly co-occur or co-exist together," he said.
"My guess is that this is opening up a new frontier."
The study appears in this week's issue of the journal PLoS ONE.
Changing Assumptions?
Ornithopods are thought to have grown in size and number in the Cretaceous period, which followed the Jurassic and lasted until about 65 million years ago. (Test your dino IQ.)
But the large Yemeni footprints suggest instead that beefier ornithopods were stomping around earlier than previously believed.
"It's a pretty large one for late Jurassic standards," lead author Schulp said, "and it tells us right now that big ornithopod dinosaurs maybe appeared a little bit earlier than was assumed so far."
Nancy Stevens, a paleontologist at Ohio University in Athens, was a co-author on the study.
"This find is encouraging," she wrote in an email, "in that it represents what we hope is the first of many discoveries from this part of the Arabian Peninsula."
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