Frozen in time beneath the desert heat: dinosaur footprints

The fossilised footprints of a herd of dinosaurs which once roamed the mudflats of what is now an arid tract of land in the Arabian desert has been discovered by scientists working in the Republic of Yemen.

It is the first time dinosaur footprints have been found in the Arabian peninsula and the researchers believe that the tracks – made by two different species of dinosaur – are just the first of many more that may lie undiscovered beneath the desert surface.

One of the set of tracks, made about 150 million years ago, are the footprints of a small herd of four-legged sauropod dinosaurs who were travelling as a group of about a dozen individuals of different sizes but at the same speed.

The other set of tracks was made by a single, two-legged ornithopod dinosaur with a distinctive footprint of three huge toes. Judging from the size of the prints and the length of its stride this ornithopod specimen was between 6 and 7 metres long from head to tail.

Anne Schulp of the Maastricht Museum of Natural History in the Netherlands said that the discovery of dinosaur footprints are unusual for this part of the world because Arabia has been relatively unexplored for fossils dating back to the Jurassic period.

“No dinosaur trackways had been found in this area previously. It’s really a blank spot on the map. It’s also a pretty remote region. Nothing grows there so why even go there in the first place?” Dr Schulp said.

The group of sauropods, which are long-necked plant-eaters, suggests they may have been part of a family group, indicating an aspect of herding behaviour that cannot always be gleaned from conventional studies of fossilised bones.

“The smaller ones are taking small steps but more quickly than the larger ones to keep up with them. So they are all moving at the same speed, but the small guys are working hard to keep up with the big ones,” Dr Schulp said.

“It’s rare to see such a big example of a dinosaur herd. This in interesting social behaviour for reptiles,” he said.

A Yemeni journalist spotted the ornithopod trackway in 2003 about 50 kilometres north of the capital Sana’a near the village of Madar. Ornithopods walked on their hind legs and ate plant material with a beak-like mouth that was able to shred and grind leaves before they were swallowed.

“One of the discerning features of the ornithopods is that they have footprints with rather blunt endings to their toes, unlike the three-toed footprints of birds which have claw on the end. Each footprint in this track was about 55 centimetres wide,” Dr Schulp said.

The study, which is published in the on-line journal Public Library of Science (PLoS), identified the second set of tracks made by the sauropod herd after excavating the immediate vicinity of the ornithopod footprints.

Dr Schulp said that the tracks went unnoticed for so long because the footprints were covered in rubble and debris and were probably too big to be identified by an untrained eye. “It isn’t a surprise that they were overlooked,” he said.

The research was carried out with the help of Nancy Stevens of Ohio University and Mohammed Al-Wosabi of Sana’s University in Yemen. The tracks are being protected by the Yemen Geological Survey and will be put on display for visiting tourists.