It almost is not fair. Carnivorous dinosaurs were armed with menacing teeth inside muscular jaws, wielded dangerous claws on their hands and feet, and boasted keen vision and sense of smell. And, as new research confirms, some were pretty fast, too.
Two trackways of Cretaceous Period fossilized footprints from about 120 million years ago discovered in northern Spain's La Rioja region show that the medium-sized meat-eating dinosaur species that made them could run at about 28 miles per hour (45 kph), scientists said on Thursday.
This roughly matches the top speed achieved by Jamaican sprinter Usain Bolt, the world's fastest human being.
Two trackways located about 65 feet (20 meters) apart were discovered, one with seven footprints and the other with five.
Each track - an impression of a three-toed foot with claws - measures around 12 inches (30 cm) long. They were made on the muddy surface of a lake plain in a region also populated by long-necked plant-eating dinosaurs, bipedal plant-eating dinosaurs, flying reptiles called pterosaurs, crocodiles, and turtles.
Speed only added to the arsenal of meat-eating dinosaurs like the species that left the footprints in Spain.
"Their capacity to run very quickly and their maneuvering abilities surely allowed them to chase prey very efficiently. And of course I wouldn't like to be caught by this guy on a riverbank," said Pablo Navarro-Lorbes, a paleontology doctoral student at Universidad de La Rioja in Spain and lead author of the research published in the journal Scientific Reports.
The footprints bore characteristics showing they were made by a theropod, a group encompassing all the meat-eating dinosaurs, including Tyrannosaurus rex. Theropods were bipedal, with the largest perhaps 50 feet (15 meters) long.
The researchers believe the trackways were made by two different individuals of the same species. They suspect it was from one of two theropod families: the spinosaurs, many of which were fish-eaters, or carcharodontosaurs, known for shark-like teeth. The individuals were about 13-16 feet (4-5 meters) long and 7 feet (2 meters) tall, weighing 440-660 pounds (200-300 kg).
Running speed was calculated based on the relationship between the animal's hip height - estimated from the footprint length - and stride length. The stride length from one of the trackways was 18.3 feet (5.6 meters), while the other was 17.2 feet (5.2 meters).
One of the dinosaurs ran 19.7-27.7 miles per hour (31.7-44.6 kph) - among the highest speed ever estimated for a dinosaur - and the other at 14.5-23.1 miles per hour (23.4-37.1 kph). One trackway indicates a smooth increase in speed. The other suggests an animal maneuvering as it ran.
Universidad de La Rioja paleontologist and study co-author Angelica Torices said speed helped not only in hunting but in fleeing danger including "bigger theropods that could see them as their prey."
Of the innumerable dinosaur tracks found worldwide, nearly all represent walking rather than running. The fastest estimated running speed based on footprints was a Jurassic Period theropod trackway in Utah at 34 miles per hour (55 km per hour).
Scientists also have calculated dinosaur speeds based on biomechanical models. The fastest using this method was the Jurassic turkey-sized theropod Compsognathus at 40 miles per hour (65 km per hour).
"There are several factors that dictate the running ability of a dinosaur," Navarro-Lorbes said.
"One of them is size. Some paleontologists think that theropods with sizes between 100 and 1,000 kilograms (220-2,200 pounds) could have been some of the best dinosaur runners because of the relationship between their weight and muscular performance," Navarro-Lorbes added, with elongated legs another key factor.