June 4, 2012
This week, I’m going to consider origin stories that go deeper into primate history than questions of when Homo sapiens evolved or when two-legged apes, or hominids, emerged.
Today, let’s go really far back, to a time some 40 million years ago known as the Eocene. Monkeys and apes weren’t even around yet, although their common ancestor was. But where? The discovery of a new species of Eocene primate is helping address that question.
Until about 20 years ago, the answer seemed obvious: Africa. That’s where the earliest fossil evidence was found, mainly from Egypt’s Fayum Depression. Starting in the 1990s, however, relevant fossils started popping up in Asia. Paleoanthropologists now consider a 45-million-year-old primate discovered in China, called Eosimias, to be the earliest anthropoid, the group of primates that includes monkeys, apes and humans. Eosimias was tiny, weighing less than half a pound. But it possessed certain dental and jaw characteristics that link it to living anthropoids.
The newly discovered species, named Afrasia dijijidae, dates to roughly 37 million years ago and was found in Myanmar. So far, all that’s known of Afrasia is based on four isolated teeth. But the nooks, crannies, crests and bumps on those teeth reveal a few things about where the ancestors of today’s monkeys and apes came from.
The species’ teeth are similar to those of the older Eosimias and other Asian species closely related to Eosimias. But the teeth’s size and shape are almost identical to those of a North African primate that lived at about the same time as Afrasia, approximately 38 million to 39 million years ago. It’s name is Afrotarsius. The findings are reported today by Jean-Jacques Jaeger of the University of Poitiers in France and colleagues in the Proceedings of the National Academy of Sciences.
The team suggests that the similarity in age between Afrasia and Afrotarsius indicates that a lineage, or lineages, of Asian anthropoids must have arrived in Africa only shortly before the appearance of Afrotarsius. If anthropoids had gotten to Africa much earlier, then Africa’s anthropoids would have evolved in their own direction, and millions of years later, you wouldn’t expect anthropoids in Asia and Africa to be so similar.
To get to Africa, anthropoids had to find a way across the Tethys Sea. The Tethys was a more sprawling version of the Mediterranean, drowning parts of northeastern Africa, the Middle East and West Asia. The small primates likely rafted over on giant mats of floating vegetation. Rafting may sound far-fetched, but researchers have suggested it’s how a variety of animals reached new land masses in the past. And around the same time that the ancestors of monkeys and apes left Asia for Africa, it appears some rodents did, too.
Come back on Wednesday for a look at the surprisingly European origins of the ancestor of Africa’s apes: chimpanzees, gorillas and humans.