A newly discovered primate that lived in Africa some 37 million years ago is somewhat of a black sheep, evolutionarily speaking. It just doesn't seem to fit into the family tree, no matter how scientists look at it.
The curiosity lies in the primate's unusual teeth, which don't match up with primate groups thought to be around at the same time. The find likely makes primate evolution on that continent more complicated, the scientists say.
"It comes as a bit of a shock to find a primate that defies classification," said study researcher Erik Seiffert of New York's Stony Brook University.
The 12 fossil teeth, the only remnants the paleontologists have of this primate so far, were found in northern Egypt. The new species is called Nosmips aenigmaticus.
During the last 30 years or so, three major primate groups have been established as being present in Africa some 55 million to 34 million years ago: early monkeys, lemur-like primates, and an extinct group called adapiforms, Seiffert said.
Nosmips' teeth place this primate in Africa at the same time. What's more, its teeth suggest it could be an evolutionary oddity that is not closely related to any of these groups.
Paleontologists usually identify primate fossils by their teeth, because teeth are the most durable parts of the body and are most likely to fossilize, and so are most likely to be recovered.
Nosmips had a rare combination of enlarged and elongated premolars with simple upper molars. It also had premolar teeth that had taken on the form of molars, instead of being relatively simple as in most other primates.
"Nosmips appears to be a highly specialized member of a previously undocumented and presumably quite ancient endemic African primate lineage" Seiffert said.
"When you find the teeth of a fossil primate, it's usually pretty clear where it fits into the family tree," Seiffert said. "There are only a few species that nobody agrees about and that really can't be placed into any of the major primate groups. These mystery fossils must have something important to tell us about primate evolution."
Right now Nosmips is one of these rare mystery fossils. Since the researchers only found its teeth, they can't be sure what the primate looked like when alive.
But they note Nosmips lived alongside another specialized primate named Afradapis, which the same team described last year in a paper published in the journal Nature. Seiffert and colleagues compared the teeth of these extinct species with those of living primates, and determined that Afradapis had adaptations for eating leaves, whereas Nosmips probably ate more fruits and insects.
"As time goes on and more discoveries are made, it will be fascinating to see how different lineages contributed to primate diversity in the Eocene of Africa," Seiffert said. (The Eocene is a time period that lasted from 54.8 million to 33.7 million years ago.)
The results will be published this week in the journal Proceedings of the National Academy of Sciences.