- From the riverbed of the Río Alto Madre de Dios in southeastern Peru, researchers have found an extremely small tooth that belonged to a species of tiny monkey that lived some 18 million years ago.
- Researchers have named the new species of extinct monkey Parvimico materdei, with parvimico meaning tiny monkey and the species name referring to the river where the fossil tooth was found.
- From the tooth, the researchers have deduced that the monkey was exceptionally small, in the size range of marmosets and tamarins, and likely ate a mix of insects and fruits.
- Given how the monkey fossil record for the period between 13 million and 31 million years ago from South America is extremely scarce, creating a gap in the understanding of the evolution of New World monkeys, the discovery of P. materdei is incredibly exciting, researchers say.
In 2016, researchers digging along the Río Alto Madre de Dios in the Peruvian Amazon uncovered hundreds of fossils of rodents, bats and other animals. Among the fossils was an extremely small tooth, “double the size of the head of a pin,” said Richard Kay, a professor of evolutionary anthropology at Duke University. This upper molar, Kay and his colleagues write in a new study, belonged to a species of tiny monkey no heavier than a hamster that lived in the region some 18 million years ago.
When the researchers first saw the tooth among the fossil collection, they immediately knew they were looking at something special.
“Monkey teeth are very diagnostic,” Kay, the lead author of the study, told Mongabay. “The team was very excited because these specimens are extremely rare.”
Kay and his colleagues have named the new species of extinct monkey Parvimico materdei, with parvimico meaning tiny monkey and the species name referring to the Río Alto Madre de Dios, on the banks of which the team discovered the fossil. The fossil tooth has now been stored in the collections of the Institute of Paleontology at Peru’s National University of Piura.
A single, small tooth can’t reveal a whole lot. But to paleontologists, the size and shape of the tooth, how worn it is, and where it was found, can say a few things about what the animal may have been like.
“The tooth’s crown is very well preserved and from the wear in life we can infer that it was a young individual,” Kay said in an email.
The researchers have also concluded that P. materdei “was an exceptionally small monkey, in the size range of marmosets and tamarins.” The monkey also likely ate a mix of insects and fruits, the researchers say, based on the tooth’s structure.
“Very small living Amazon monkeys (especially the marmosets) feed mostly on a mix of fruit and tree exudates (gum),” Kay said. “Parvimico lacks the gum component in its diet.
“We can say nothing more reliably about its social habits or mode of locomotion, although tree living is probable because all known South American monkeys are arboreal,” he added.
A tiny tooth may not seem like much. But fossil records of primates from South America are rare, which means that even a fossil tooth is a big deal. In fact, P. materdei is the first named Early Miocene primate from the Amazon Basin, the researchers write in the paper.
The rarity of primate fossils in South America is “because the overall biomass of South American monkeys is very low compared with that of small rodents (of which we have many specimens) and marsupials,” Kay said. “Also, monkeys have long life spans and slow reproductive rates compared with rodents of similar size, so the rate of turnover is slower.”
Given how scarce primate fossils from the region are, P. materdei fills a gap in understanding the evolution of New World monkeys.
Researchers posit that monkeys reached South America from Africa some 40 million years ago. In South America, they diversified into the more than 150 species of New World monkeys known today, most of them living in the Amazon rainforest. However, the monkey fossil record for the period between 13 million and 31 million years ago from the region is extremely scant, and includes just a few fragments of teeth and jaws.
P. materdei dates back 17 million to 19 million years, placing it “smack dab in the time and place when we would have expected diversification to have occurred in the New World monkeys,” Kay said in a statement.
In fact, sediments on the banks of the Río Alto Madre de Dios are rich in fossils and are helping Kay’s team reconstruct what life was like in the Amazon 18 million years ago. The location is especially important to retrace the evolution of primates.
“The proximity to the Andes is the key,” Kay said. “As the Andes rose through the Cenozoic, the adjacent originally flat-lying sediments in the piedmont region were folded, then eroded flat. Rivers crosscut the ancient sediments bringing the rock units to the surface. By contrast in the central Amazon basin, the older sediments are still deeply buried. The few other geologically old primate specimens recovered, of which there are only 4 or 5 teeth, share the same proximity to the Andes.”
Kay, R. F., Gonzales, L. A., Salenbien, W., Martinez, J. N., Cooke, S. B., Valdivia, L. A., … & Baker, P. A. (2019). Parvimico materdei gen. et sp. nov.: A new platyrrhine from the Early Miocene of the Amazon Basin, Peru. Journal of Human Evolution, 134, 102628. doi: 10.1016/j.jhevol.2019.05.016