Not all two-legged dinosaurs were like the lumbering Tyrannosaurus rex. An analysis of dinosaur tracks from 120 million years ago unearthed in Spain adds to growing evidence that these meat-eating prehistoric beasts belonging to the same group as T.rex could be highly agile. The findings, published Thursday in Scientific Reports, reveal one of the fastest known sets of fossilized dinosaur footprints. Also readChina dinosaur footprint fossil named after Doraemon's "Nobita":  These tracks join the ranks of other speedy sets found in Utah and Texas, one of which shows dinosaurs running at speeds over 30 mph. The Spanish footprints showed speeds of nearly 28 mph. To calculate the running speed, scientists measured the length of the footprint and took into account the dinosaur's hip height and stride length — the distance between two consecutive footprints of the same foot. All of the fastest known sets of prints come from a family of dinosaurs called theropods. These carnivorous dinosaurs stood on two legs and could not fly, like the famed velociraptor. The animals that created the most recent impressions were probably 5 to 6 1/2 feet tall and 13 to 16 feet long from mouth to tail, the researchers estimated. Scientists think there may be other faster dinosaurs, but the tracks of theropods have been easier to track down. “Behavior is something very difficult to study in dinosaurs,” said lead author Pablo Navarro-Lorbés of the University of La Rioja. “These kind of findings are very important, I think, for improving that kind of knowledge.” Also read: Dinosaur footprints found in ancient Chinese imperial resort Scientists typically predict dinosaur behavior through computer modeling of the creatures' movement. Physical examination of fossilized footprints confirm the results. These are “clearly active, agile animals," said Smithsonian paleontologist Hans Sues, who had no role in the study.

Fossilized footprints discovered in New Mexico indicate that early humans were walking across North America around 23,000 years ago, researchers reported Thursday. The first footprints were found in a dry lake bed in White Sands National Park in 2009. Scientists at the U.S. Geological Survey recently analyzed seeds stuck in the footprints to determine their approximate age, ranging from around 22,800 and 21,130 years ago. The findings may shed light on a mystery that has long intrigued scientists: When did people first arrive in the Americas, after dispersing from Africa and Asia? Also read: Egypt team identifies fossil of land-roaming whale species Most scientists believe ancient migration came by way of a now-submerged land bridge that connected Asia to Alaska. Based on various evidence — including stone tools, fossil bones and genetic analysis — other researchers have offered a range of possible dates for human arrival in the Americas, from 13,000 to 26,000 years ago or more. The current study provides a more solid baseline for when humans definitely were in North America, although they could have arrived even earlier, the authors say. Fossil footprints are more indisputable and direct evidence than “cultural artifacts, modified bones, or other more conventional fossils,” they wrote in the journal Science, which published the study Thursday. “What we present here is evidence of a firm time and location,” they said. Based on the size of the footprints, researchers believe that at least some were made by children and teenagers who lived during the last ice age. David Bustos, the park's resource program manager, spotted the first footprints in ancient wetlands in 2009. He and others found more in the park over the years. Also read: Fossil leaves may reveal climate in last era of dinosaurs “We knew they were old, but we had no way to date the prints before we discovered some with (seeds) on top,” he said Thursday. Made of fine silt and clay, the footprints are fragile, so the researchers had to work quickly to gather samples, Bustos said. “The only way we can save them is to record them — to take a lot of photos and make 3D models,” he said. Earlier excavations in White Sands National Park have uncovered fossilized tracks left by a saber-toothed cat, dire wolf, Columbian mammoth and other ice age animals.