Wednesday, 13 June 2012

A Revolution In Primate Prehistory

In 2009, a media storm hit the world, proclaiming the discovery of our oldest primate ancestor: Darwinius masillae. It was discovered in the remains of a 47 million year old lake bed in Germany. Yet once the excitement had died down, and after objective examination, it was shown that Darwinius was most likely to be close to the base of the primate family tree rather than the first of the group. It was still, however, a major discovery; and backed up the theory that primates, and their more advanced descendants including humans, evolved in Africa and Southern Europe. A model which has prevailed for many years.

Now, after sifting through tonnes of alluvial sediment for six years, a team have made a remarkable new find which challenges this long-held view of primate evolution. Led by Chris Beard, a palaeontologist from the Carnegie Museum of Natural History, the team excavating at the Eocene Pondaung formation near Nyaungpinle in central Myanmar, have recovered fragmentary remains of a creature, closely related to primates, which existed on the other side of the world in Northern Africa.

The Pondaung formation in Myanmar
They came away with just four, 37 million year old teeth from a primate they named Afrasia djijidae. It might seem a bad idea to name an entirely new species from a handful of teeth. Yet mammals have groove patterns on their teeth unique to the species. If no match comes up, it must be new. Indeed most of the early mammal species on Earth are only known about from single teeth. The process, however, is laborious.

Neil Shubin, the famous early tetrapod palaeontologist described mammal palaeontology as 'dentistry 101.' The same team had discovered teeth from another developmental primate, Ganlea megacanina, at the same formation. The area itself is well known for remains of the earliest advanced primates (properly called anthropoids) in South East Asia, but this creature had something rather different.

The 37 million year old teeth of Afrasia djijidae
Its morphology was very similar to that of Afrotarsius libycus, another anthropoid which had been discovered in rocks of a slightly younger age on the other side of the world in the deserts of Libya. It suggested that the advanced, or higher primates, had evolved in Asia and then migrated west. 'Reconstructing events like the colonization of Africa by early anthropoids is a lot like solving a very cold case file,' says Beard. 'Afrasia may not be the anthropoid who actually committed the act, but it is definitely on our short list of prime suspects.'

From Darwinius to Afrotarsius, there is a 10 million year gap. It was previously thought that Africa's primate fossil record was simply poor. This new discovery suggests that it simply does not exist, yet started with Afrotarsius which evolved from the first Asian anthropoids. The discovery may have implications which extend beyond the evolution of the higher primates and humans. It was once thought that the American primates evolved from African ancestors, carried across the Atlantic ocean on chunks of mangrove swamp which broke away from the coast during intense storms.

While fossils of flightless avians of a similar species, on both continents within the same date period, backed up this theory, it was still a long shot. If, in fact, the American primates evolved from early Asian anthropoids, this would rule out the need for a long distance crossing of a dangerous ocean. 'Afrasia is a game-changer because for the first time it signals when our distant ancestors initially colonized Africa. If this ancient migration had never taken place, we wouldn't be here talking about it.'