By Helen Briggs
Science reporter, BBC News
Dinosaur footprints made 150 million years ago in the bedrock of what is now Yemen are the first to be discovered in the Arabian Peninsula, say scientists.
The two separate trackways were made by a herd of 11 sauropods, and a lone two-legged plant-eating dinosaur belonging to the ornithopod family.
They went unnoticed for so long because they were covered by rubble and debris.
The fossil record in the area is very sparse, with only a handful of dinosaur remains known to science.
A Yemeni journalist stumbled upon the first set of impressions in the village of Madar north of the capital Sana'a.
They were later classified as belonging to an ornithopod, a large, common, two-legged dinosaur that flourished from the Late Triassic Period to the Late Cretaceous Period.
In 2006, a geologist at Sana'a University in Yemen made a further discovery - a set of round and elephant-like footprints from a different dinosaur family, the giant four-legged long-necked sauropods.
Dr Anne Schulp of the Maastricht Museum of Natural History in the Netherlands went out to Yemen to help in the investigation. He said the tracks were "beautifully preserved".
"The nice thing about the sauropod tracks is that we've got a herd of them, 11 individuals all walking in the same direction," Dr Schulp told BBC News.
"It's actually a group consisting of different-sized animals, so we've got old ones and we've got some younger dinosaurs as well, so different age-groups of dinosaurs were living together here."
The sauropod trackway has been preserved by geologists
Only a few dinosaur fossils have been reported so far from the Arabian Peninsula, including isolated bones from Oman and possible fragments of a long-necked dinosaur from Yemen.
"It's the first time we've found dinosaur trackways in the Arab Peninsula so it really is a first," said Dr Schulp.
"It's a bit of data from a place that we really don't know much about yet. There is a lot of potential for more discoveries."
Palaeontologist Dr Paul Barrett of London's Natural History Museum said the findings, published in the journal PLoS One, considerably expand our knowledge of Middle Eastern dinosaurs.
"Dinosaur material is exceptionally rare in this part of the world, and is represented by only a handful of fragmentary fossils," he said.
"As a result, we know virtually nothing about the animals that once roamed this area. This discovery shows that several different kinds of dinosaur were abundant in the region and starts to fill a large gap in our knowledge of what was going on in the Middle East during the age of the dinosaurs."