Thursday, 23 February 2012

A Herd Of Ancient Four Tusked Elephants

One of the most iconic images connected with Africa is of a herd, or perhaps more accurately family group, of elephants slowly making their way across the burning sands of the Saharan Desert. The family group is headed by a single matriarch, responsible for hundreds of younger females and juvenile members. Occasionally the males travel with these groups but mostly they live either alone or in a loose male herd. The question is was this behavior present in the many different species of prehistoric elephant?

It is possible to use their anatomical features to deduce diets, size, even mating rituals. Yet they do not give us any insight into their social lives. However a recent fossil discovery in the Arabian Desert might provide an answer. In January 2011, researchers from the Natural History Museum in Berlin, led by vertebrate palaeontologist Faysal Bibi, mapped an area of the Arabian Desert known as Mleisa 1 that contained a series of fossil tracks. They had been known about for a long time and were thought by locals to have been made by giants of ancient myth, and by palaeontologists by dinosaurs.

A reconstruction of the Mleisa 1 herd. The cluster of elephants
are females and juveniles while the single set are those of a male
The team's survey of the area revealed something very different. First and foremost, the rocks in which the tracks were preserved were just 7 million years old, far too young for any dinosaur or other ancient reptile to have made them. The tracks, 40 centimetres in diameter, were quite round and lacked the types of indentation specific to dinosaurs. Using a pocket digital camera strapped to a kite, the team took images of the 260 metre stretch of imprints and stitched them together into a single reconstruction of the Mleisa 1 site.

They concluded that they were made by 13 individuals of varying ages, gender and size. As they covered an area equivalent to the base of the Great Pyramid of Giza, making them the largest set of mammalian fossil tracks anywhere in the world, there was enough information to accurately reconstruct the composition of the herd. 12 of the tracks were grouped closely together. They belonged to females and juveniles, suggesting that they were a family group.

An artist's impression of the Mleisa 1 herd of Stegotetrabelodon syrticus
The 13th set belonged to a solitary male making his way away from the herd. 'The trackways are visually stunning,' said researcher Andrew Hill at the University of Poitiers in France. 'It is quite obvious to anyone, without any technical knowledge, that these are the footprints of very large animals, and to learn that they are over 6 million years old presents a visitor with the sensation of walking back in time.' The fossils themselves belonged to a four-tusked species of elephant called Stegotetrabelodon syrticus.

The data from the tracks shows that, despite its prehistoric nature, the creatures probably lived in hierarchy based groups similar to those of modern elephants. What is more, Stegotetrabelodon is the last common ancestor of African and Indian elephants, meaning that this hierarchy based lifestyle probably evolved early on in proboscidean evolutionary history (proboscideans are a group of mammals with trunks, including mammoths, modern elephants and the various extinct forms such as Stegotetrabelodon).

'Like the human handprints in Paleolithic caves, animal trackways crystallize in time the identity and behavior of the organisms that made them, and yield rare insights about these organisms, which fossil bones alone cannot provide,' said paleontologist William Sanders at the University of Michigan, who did not take part in the study. More trace fossils, such as tracks or feeding remains, will reveal more about these older proboscideans and their social lives.