杏吧原创

Our distant primate ancestors are聽thought to have arisen in Asia, but new evidence challenges this assumption, suggesting primates may instead have evolved in Europe or North America.

Primates include all lemurs, monkeys, apes and humans. The oldest confirmed primate fossils are about 56 million years old, so were formed 10聽million years after the extinction that wiped out all dinosaurs except birds. This time is called the Palaeocene-Eocene Thermal Maximum because the average global temperature rose by 5掳C or more in a few thousand years. Many ocean species died out, but life on land flourished. Primates emerged, as did the first hoofed mammals.

The established story has been that primates appeared at this time in Asia, says anthropologist Paul Morse. This is based on the discovery in China of several fossils of primitive primates that聽resemble miniature monkeys聽or bushbabies. These include Archicebus achilles as well聽as Teilhardina asiatica, which聽is thought to be one of the聽earliest primates.

But other Teilhardina species have been found elsewhere, and聽seem to be just as old. These include Teilhardina belgica in Europe and Teilhardina brandti and several other species in 狈辞谤迟丑听础尘别谤颈肠补.

To better understand early primates, Morse 鈥� while working at the Florida Museum of Natural History 鈥� and his colleagues collected 163 new T. brandti fossils聽from the Bighorn Basin in Wyoming, and compared them with other Teilhardina species (Journal of Human Evolution, ).

鈥淲hat we found, once we had evaluated the variation within 罢.听产谤补苍诲迟颈, was that it closely resembled the animal from China聽[罢.听补蝉颈补迟颈肠补],鈥� he says. 鈥�罢.听产别濒驳颈肠补 also has some of these characteristics. They鈥檙e all about on par with one another in their primitiveness.鈥�

That means T. asiatica cannot be reliably distinguished from either Europe鈥檚 T. belgica or North America鈥檚 T. brandti.

鈥淲herever primates began, the group spread remarkably rapidly once they had emerged鈥�

If we can鈥檛 determine which fossil is the most primitive, we also can鈥檛 tell where primates evolved. Morse emphasises that he isn鈥檛 claiming North America is their cradle, rather than Asia, but that the question remains open.

However, Christopher Beard at聽the University of Kansas, who co鈥慸iscovered A. achilles, argues that primates must have arisen in Asia, by process of elimination. 鈥淭here鈥檚 nothing in either Europe or North America that鈥檚 a likely ancestor for these things,鈥� he says.聽鈥淪o I think most of us have basically given up on Europe and North America being places where聽these animals might have originally evolved.鈥� He points to Asian groups of tree shrews and the lemur-like gliding colugos as potential ancestors of primates.

But Morse thinks that the extinct plesiadapiforms聽鈥� a large group of squirrel-like animals that lived in Asia, Europe and North America 鈥� could have given rise to the first primates. 鈥淪ome aspects of their teeth closely resemble the聽teeth of early primates,鈥� says Morse. A few plesiadapiforms seem to have adaptations in their ankles that closely resemble features seen in early primates that are thought to have been used for grasping, he says.

Regardless of where primates began, the group spread remarkably rapidly once they had聽emerged. 鈥淗ow did they go from being nowhere to being on all three northern continents?鈥� asks Morse.

He thinks the spread of forests, driven by the warmer climate, gave them an uninterrupted habitat through which to move.

This article appeared in print under the headline 鈥淩ethinking the origins of primates鈥�