Just how the primate family reached South America from Africa remains a mystery. However they did it, it had been thought that only one lineage of monkeys reached the New World, around 32 to 36 million years ago.
Not so, it seems. Researchers, to their shock, have found evidence of a second lineage of early monkeys that strongly resemble archaic monkeys found in Africa.
But that second lineage went extinct, albeit after more than 11 million years, paleontologists reported Thursday in a journal of the American Association for the Advancement of Science.
The first lineage is still there. The discovery is based on exactly four tiny fossilized teeth found in the Peruvian Amazon that proved to be profoundly unlike the teeth of that first known lineage, the platyrrhini. Evidently a second early monkey also accidentally rafted over the briny.
The newly discovered extinct early monkey in Peru has been named Ucayalipithecus perdita, and the analysis concludes that it originated in a primitive African higher primate (which is the category of monkeys and apes; lower primates are lemurs, lorises and tarsiers).
Regarding the nomenclature, “Ucayali” is for a Peruvian department bordering Brazil, pithekos is Greek for monkey or trickster and perdita is Latin for lost.
So how did the lost Peruvian trickster early monkey, and the ancestors of the platyrrhini, travel somewhere between 1,500 to 2,000 kilometers (1,243 miles) across the paleo-Atlantic? And what happened to it?
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No fossils of platyrrhini (ancestors of today’s South American monkeys) have been found in North America. One might expect to have found some if there were any, because North America has an extensive fossil record, Prof. Marc Godinot of Ecole Pratique des Hautes Etudes points out in an analysis in the journal.
Also, North America is nothing if not paleontology-oriented. Also, when these ancestral mammals made their involuntary crossings, sea levels were relatively low, Erik Seiffert of the University of Southern California and colleagues note in their paper published in the journal.
So absent other theories, the conclusion is that the hapless early monkeys “sailed” or “rafted” – they got washed into the turbulent seas clinging to floating logs and somehow survived their trans-Atlantic adventure, thanks to fortuitous ocean currents.
If it helps buy that odd scenario, caviomorph rodents also apparently crossed the pond at least 41 million years ago, Godinot explains, floating on vegetation rafts, because they exist in Africa and South America but haven’t been found in North America. (Maybe monkeys and rodents crossed together and it doesn’t bear thinking who ate what en route, but the primate and rodent dispersals seem to be separated by some 10 million years.)
The bottom line is that the Ucayalipithecus fossil teeth found in Peru near the Brazilian border are extremely close to similar well-dated fossils from African parapithecid primates found in Egypt, Libya and Tanzania. They couldn’t have been ancestral to the platyrrhini, Seiffert and the team conclude. So (at least) two monkey groups rafted over the seas from Africa.
Swinging by the tails
Today, around 35 million years after their ancestors parted ways, New World monkeys differ from their African cousins in myriad ways. The American monkeys have flat noses (hence the name “platyrrhini”) with nostrils facing sideways, while African catarrhine monkeys have snouts with the nostrils facing down. The American monkeys’ nostrils are further apart. New World monkeys have long prehensile tails that can help them master the arboreal lifestyle, while African monkeys’ tails can’t grasp branches.
A wondrous additional difference is that the African monkeys have opposable thumbs but the American ones don’t. Their thumb is on the same plane as their other fingers.
The two sides’ social style is also disparate enough to warrant attention. African monkeys tend to form groups with one dominant male and multiple ladies, and they don’t help with the offspring. American monkeys tend to form groups with one female and multiple males who do help with the kids.
We humans arose from African primates tens of millions of years after the catarrhine and platyrrhini separated. With all due respect to monogamy, marriage and fidelity, we are catarrhinic in our habits.
And teeth also evolved radically over the eons. The Ucayalipithecus’ molars are lumpier and more bulbous than that of the platyrrhini. They look like the molars of the African Parapithecidae, which lived in North Africa from 23 to 56 million years ago (the Eocene and Oligocene periods).
Ucayalipithecus split from its African sister taxon, the Qatrania, about 35.1 million years ago, the team estimates, which would date the trans-Atlantic adventure that gave rise to the Ucayalipithecus lineage between 31.7 and 35.1 million years ago.
But what happened to them? However they arrived, we have flat-nosed monkeys in South America to this day, but Ucayalipithecus went extinct – though first they crossed the ocean and then the continent to the location the teeth were found in the Peruvian Amazon.
It must have been extremely challenging to adapt to the new environment, but they did it, for a long time. In fact, the Ucayalipithecus was likely found throughout prehistoric South America. Why they died out and the platyrrhini went on to conquer the canopy remains a mystery.