Ancient tracks are elephant herd
A seven-million-year-old trail of fossilised footprints in the Arabian desert was left by a herd of ancient elephants, according to scientists.
Researchers say the "trackways" reveal that animals that left them had a rich and complex social structure.
Just like modern elephant society, this consisted of family herds and of solitary male animals.
The study is published in the Royal Society journal Biology Letters.
End Quote Prof Adrian Lister Natural History Museum, London
They're completely unique saucer-like depressions”
Lead researcher Dr Faysal Bibi, a palaeontologist based at the University of Poitiers in France and the Museum of Natural History in Berlin, Germany, described the footprints as "fossilised behaviour".
Dr Bibi explained to BBC Nature that there were two different sets of tracks across the site.
"We have tracks from a herd, from which we calculated the size profile [of each animal]," he said.
"And, just by luck, we also have the trackway of a solitary individual travelling almost perpendicular to the herd."
Dr Bibi described the site as "absolutely unique".
"[It's] a really rare opportunity in the fossil record that lets you see animal behaviour in a way you couldn't do with bones or teeth," he said.
Although the area near Abu Dhabi in the United Arab Emirates has been known to locals for generations, it was first studied by scientists in 2001.
Dr Bibi explained that a colleague of his, Mark Beech, was taking part in an archaeological excavation nearby.
"A local man named Mubarak Bin Rashid al-Mansouri - who knows the desert there like the back of his hand - led [Mark] to the site," he explained.Kite photography
The sheer size of the trackway site meant that the best way to study it in its entirety was to photograph it in detail from the air.
On of the team, Dr Nathan Craig from Pennsylvania State University in the US, designed and built a "kite camera" - attaching a remotely operated camera to a kite and using it to take thousands of images.
With these he was able to create a detailed mosaic of the entire site.
"Once we saw it from the air, we realised what we had here," recalled Dr Bibi.
"We're talking about a site of about five hectares (50,000 square metres); as far as we know, it's the largest fossil trackway in the world."
The continuous "herd track" was made by at least 13 individual animals of different sizes and ages.
This was transected by a solitary track of footprints, left by a much larger animal, probably a solitary male.
Among modern elephants, Dr Bibi explained, "once males hit sexual maturity, they tend to leave the herd and lead these solitary lives".
"Here, at seven million years ago, we have this beautiful snapshot of that same social behaviour."
Although modern Asian and African elephants were already living at the time, the team think the tracks were most likely to have been left by the "grandparent of modern elephants", the now extinct Stegotetrabelodon.
Prof Adrian Lister from the Natural History Museum in London said the trackways were "fabulously evocative".
"It's incredibly graphic, even before the science," he commented.
"You can tell that these are elephant footprints... They're completely unique, big saucer-like depressions."
And the fact that the herd's footprints never crossed one another, he explained, provided a strong indication that this was indeed a herd walking together, rather than individual animals crossing the same site at different times.
Prof Lister added: "It suggests that some of the elements of the social structure that we see in modern elephants was already evident in their ancestors at this time."