In 1967, George Gaylord Simpson, a palaeontologist, found a 20-million-year-old fossil in Chamtwara in western Kenya.
It wasn’t much: three lower jaw bones, each barely an inch long, and a handful of teeth, less than three millimetres across. He classified it as a member of the loris family, which are nocturnal primates with enormous eyes, and called it Propotto leakeyi.
However, a colleague convinced him that the bones belonged to a fruit bat.
With the creature’s identity settled, the fossil took a spot at the National Museums of Kenya, until two years ago, when another palaeontologist (a scientist who studies fossils) took a fresh look.
Like Simpson, he thought the creature’s hind teeth were more reminiscent of a primate than a bat.
He also noted that the stump of a broken front tooth would have jutted out from its mouth like a dagger – a trait only known in aye-ayes, the only living primates with rodent-like teeth.
This re-examination saw scientists analyse more than 395 anatomical features and 79 genes from 125 mammal species, both living and extinct.
The researchers also compiled microCT scans of the lower molars of 42 living and extinct mammal groups including bats, tree shrews and primates.
They used a computer programme to compare the bumps, pits and ridges of Propotto’s teeth to those of other animals, and found that Propotto shared a number of features with another buck-toothed primate that lived in Egypt 34 million years ago.
Both Propotto and the Egyptian primate were ancient relatives of the aye-aye, which branched out into the lemur family tree.
Before this discovery, researchers had long believed that lemurs, which are also distant primate cousins of humans, made their way to Madagascar, the only place where they are found, 60 million years ago in a single wave, and became the first mammals to colonise the island.
Now researchers propose that there were two separate lemur lineages, which split in Africa before heading to Madagascar, and they may have arrived on the island independently, and much later than previously thought.
One lineage eventually led to the aye-aye, which split from the rest of the lemur family tree 40 million years ago, while the other led to all other lemurs.
The findings also debunk the long-held view that lemurs were the first mammals to colonise Madagascar.
Instead, they suggest that they arrived around the same time as other mammals, such as rodents, Malagasy mongooses, and hedgehog- and shrew-like animals called tenrecs.
Moreover, frogs, snakes and lizards may also have made the trip from mainland Africa to the island at the same time.
Because lemurs can’t swim, the scientists think they crossed the 402-kilometre-wide channel between mainland Africa and Madagascar after being swept out to sea in a storm, and holding onto broken trees or floating vegetation before washing ashore.
“But if the arrival were more recent, they might have had a shorter distance to travel, thanks to lower sea levels when the Antarctic ice sheet was much larger.
“It is possible that lemurs weren’t in Madagascar at all, until maybe the Miocene, as recently as 23 million years ago.
“Either way, the fossils tell us something we never could have guessed from the DNA evidence about the history of lemurs on Madagascar,” said Doug Boyer, an associate professor of evolutionary anthropology at Duke University in the US, who took part in compiling scans of the fossil’s molars.
he findings were published in the journal Nature Communications.