Ancient footprints in the Arabian Desert have left intriguing evidence about how elephant ancestors interacted socially.
An international team of researchers analysed the five hectare fossil trackway site, known as Mleisa 1, in the United Arab Emirates. It features exceptionally long trackways of a single herd of at least 13 individuals, ancestors to modern-day elephants, probably Stegotetrabelodon syrticus, which had tusks in both its upper and lower jaws. There is also an intersecting trail of a lone, larger elephant-like creature. At more than 260 meters long, the latter trackway is among the longest fossilized mammalian route ever recorded.
An international team from Germany, France, the United States, and the United Arab Emirates published the study in Biology Letters on February 22, 2012. Primary author Faysal Bibi is a researcher at the Institut International de Paléoprimatologie, Paléontologie Humaine: Évolution et Paléoenvironnements in Poitiers, France, and the Museum für Naturkunde in Berlin, Germany. Co-authors are Brian Kraatz, assistant professor of anatomy at Western University of Health Sciences; Nathan Craig, assistant professor of anthropology at Pennsylvania State University; Mark Beech, Abu Dhabi Tourism and Culture Authority; Mathieu Schuster, research associate, Université de Strasbourg, France; and Andrew Hill, professor of anthropology, Yale University.
"It's like walking back in time," said Hill. The herd walked through mud and left footprints that hardened, were buried, and then re-exposed by erosion. Analysis of trackway stride lengths reveals the herd contained a diversity of sizes, from adults to a young calf, making this the earliest direct evidence of social structure in prehistoric elephants ever discovered.
"Basically, this is fossilized behavior," says Bibi, "This is an absolutely unique site, a really rare opportunity in the fossil record that lets you see animal behavior in a way you couldn't otherwise do with bones or teeth."
Plainly visible in the crusty surface of the desert, the footprints were known to researchers for several years. But the inherent relationships among them only became clear after researchers produced and analysed a detailed photo mosaic of the area using high-resolution aerial cameras.
"Once we saw it aerially, it became a much different and clearer story," Kraatz said. "Seeing the whole site in one shot meant we could finally understand what was happening."
Co-author Nathan Craig used a camera-mounted kite to take hundreds of aerial photos that were then digitally stitched together to form a highly accurate photomosaic of the site.
Mleisa 1 is one of many fossil sites of the Baynunah Formation, a sequence of mostly river-deposited sands that is widely exposed over the Al Gharbia region of Abu Dhabi Emirate. Most Baynunah sites have yielded fossilized bones showing a diversity of animals lived in the Arabian Peninsula in the late Miocene Epoch, between six and eight million years ago.
The Baynunah rocks and fossila indicate that at this time, a river system came across the Arabian Peninsula through what is today the United Arab Emirates. The freshwater ecosystem supported a thriving African-like fauna during that time.
A great diversity of animals lived in the area then, including elephants, hippopotamuses, antelopes, giraffes, pigs, monkeys, rodents, small and large carnivores, ostriches, turtles, crocodiles and fish. Although there is evidence that desert conditions existed then as now, these creatures were sustained by the very large river system, along which was flourishing vegetation, including large trees.
The river subsequently dried up and those animals disappeared, including the elephant ancestors whose prints are preserved at Mleisa 1. The Baynunah Formation sites in Abu Dhabi Emirate are the only such fossil sites known from this time period from the entire Arabian Peninsula.