LA RIOJA (REUTERS) - 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 fossilised 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 45kmh, scientists said on Thursday (Dec 9).
This roughly matches the top speed achieved by Jamaican sprinter Usain Bolt, the world's fastest human being.
Two trackways located about 20m 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 30cm 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 Mr 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 15m 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 4mto 5m long and 2m tall, weighing 200kg to 300kg.
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 5.6m, while the other was 5.2m.
One of the dinosaurs ran 31.7kmh to 44.6kmh - among the highest speed ever estimated for a dinosaur - and the other at 23.4kmh to 37.1kmh. One trackway indicates a smooth increase in speed. The other suggests an animal manoeuvring as it ran.
Universidad de La Rioja paleontologist and study co-author Angelica Torices said speed helped not only in hunting but also 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 55kmh.
Scientists also have calculated dinosaur speeds based on biomechanical models. The fastest using this method was the Jurassic turkey-sized theropod Compsognathus at 65kmh.
"There are several factors that dictate the running ability of a dinosaur," Mr Navarro-Lorbes said.
"One of them is size. Some paleontologists think that theropods with sizes between 100kg and 1,000kg could have been some of the best dinosaur runners because of the relationship between their weight and muscular performance," he said, adding that elongated legs were another key factor.