In the Steps of Ancient Elephants

One day, sometime around seven million years ago, a herd of bizarre, four-tusked elephants crossed the desert that stretched over what is now the United Arab Emirates. Thirteen of the behemoths plodded along together, perhaps moving towards one of the wide, slow rivers which nourished stands of trees in the otherwise the arid region. Sometime later, a solitary animal trudged across the herd’s path in another direction. We know all this because paleontologists have found the tracks of these massive animals.

Scientists were not the first people to wonder about the fossil footprints. The huge tracksite – which stretches over an area equivalent to seven soccer fields – had been a source of speculation among local Emirati people for years. Dinosaurs and even mythical giants were thought to have been responsible for the potholes. It wasn’t until the spring of 2001 that a resident of the area, Mubarak bin Rashid Al Mansouri, led researchers from the Abu Dhabi Islands Archaeological Survey to the immense fossil field.

Dinosaurs had not created the tracks. The snapshot of time represented by the trace fossils came from the Miocene, sometime between six and eight million years ago — all the gargantuan non-avian dinosaurs had died out over 60 million years previously. Based upon the geological context and what had been found in the area before, fossil elephants were quickly identified as the trackmakers. The site was named Mleisa 1.

Researchers Will Higgs, Anthony Kirkham, Graham Evans, and Dan Hull published a preliminary report on the trackway in 2003. But the full scope of the site has not been understood until now. With the help of a Canon S90 pocket camera rigged up to a kite, a multidisciplinary team of scientists led by Faysal Bibi from the Humboldt University of Berlin  and Brian Kraatz of the Western University of Health Sciences have finally been able to stitch together a brief glimpse into the social lives of prehistoric elephants. The team published their study today in Biology Letters.

The paper presents an direct look at fossil elephant social structure. Such peeks into prehistoric behavior are rare. While many archaic elephant tracks have been found before – going back to about 9 million years ago – these often record the movements of solitary animals. No one had ever found traces left by an entire herd before. The Mleisa 1 trackway is truly exceptional.

Based upon the assembled photograph of the site, Kraatz and co-authors counted at least thirteen elephants of different sizes in the herd.  Exactly which species of prehistoric elephant they belonged to is unknown. At least three different elephants existed in the area at the time,but, based upon fossil abundance and the paleoecology of the elephants, the researchers suggest that the tracks were created by Stegotetrabelodon. Although roughly the same size as modern elephants, this kind of proboscidean had a long, low skull with four conical tusks jutting out of its jaws.

That these animals were probably moving together is revealed by the organization of the tracks. “The consistent preservation of the prints in the herd and their close parallel orientation,” Kraatz said, indicates that the tracks “were all created then desiccated at around the same time.” This major trackway stretches for over 190 meters. And there’s another, even longer trackway at the site. A 260 meter long trail records the movements of a single, large individual sometime after the herd passed by.

Was the large herd primarily composed of females and led by a matriarch, like modern elephants? That is difficult to determine. The tracks themselves do not offer definitive evidence of sex. But Kraatz and co-authors suggest that the prehistoric elephants had a social structure similar to their living cousins. Since males of modern elephant species leave their herds when they reach sexual maturity, the same might have been true of the prehistoric species. The solitary individual, therefore, might be a male, and the herd might therefore be composed of females.

Lacking soft tissues or even fossil bones to study, size makes all the difference. Since mature male elephants are typically larger than females, a size difference between the solitary animal and the largest member of the herd would be consistent with the idea that the lone elephant was a male. Frustratingly, though, the study concluded that the lone trackmaker and the largest members of the herd were about the same size. Still, Kraatz pointed out that there might be a few clues that the solitary individual was a male, after all. “The stride length of our solitary individual is longer than any [individual] in the herd,” Kraatz said, and this is consistent with the idea of the animal being a male. Likewise, Kraatz noted, “the left-right print widths of the solitary individual are also wider than any of those in the herd – another indicator that it was bigger.” This would mean that, like modern elephants, males in this prehistoric species left their herds as they became sexually mature and often traveled alone, while females would group together in herds.

The trackway indicates that prehistoric elephants were forming herds by seven million years ago at the latest. And, since Stegotetrabelodon is a relatively distant cousin of modern elephants, herding behavior may have originated at a much earlier time and been shared by various prehistoric species. “We know that the two elephant species today show female-led family groups, and this study shows that such behavior extends beyond their last common ancestor, if indeed, the track maker was Stegotetrabelodon,” Kraatz said. That is the wonderful thing about fossil trackways. The traces record a few moments of prehistoric time in which we can walk in the footsteps of fantastic prehistoric creatures. As Kraatz himself put it, “The most-interesting part here, in my mind, is not what the is answer to the question about the antiquity of this behavior, it’s that the fact we could even date it back this far. This is nothing short of amazing considering the difficulties in inferring any sort of behavior from fossils.”

References:

Bibi, F., Kraatz, B., Craig, N., Beech, M., Schuster, M., and Hill, A. 2012. Early evidence for complex social structure in Proboscidea from a late Miocene trackway site in the United Arab Emirates. Biology Letters, XX:XXX-XXX. doi: 10.1098/rsbl.2011.1185

Higgs, W., Kirkham, A., Evans, G., Hull, D. 2003. A Late Miocene Proboscidean Trackway from Western Abu Dhabi. Tribulus, 13 (2), 3-8