Monkeys on a raft — is the only way to explain species on two continents ???

This mind-boggling story is way TOO COOL, bordering on heresy. 😉 Scientists have long been skeptical with the suggestion that small mammals crossed large oceanic barriers to populate faraway lands — millions of years ago…!! However, progress in phylogenetics during the 1980s has forced researchers to reconsider that North American fossil records showed no relatives of South American caviomorph rodents or platyrrhine (New World) monkeys, and that their closest relatives lived on the Afro-Arabian landmass during the Eocene epoch (56 to 34 million years ago). Therefore, to reach South America, these animals would have had to cross the South Atlantic Ocean — which probably was more than ~1500 to 2000 km (~930 to 1240 miles) wide during this period.

Authors [see attached article & editorial] report on fossils from Santa Rosa in Amazonian Perú, that provide evidence of a

third mammalian lineage of African origin that briefly appeared in South America in the early Oligocene (35 to 32 million years ago): a now-extinct parapithecid anthropoid monkey (genus: Ucayalipithecus). These data: (i) provide the most compelling phylogenetic link yet of a South American fossil mammal to an Afro-Arabian clade; (ii) substantially constrain the timing of the transatlantic dispersal that gave rise to this South American parapithecid lineage and possibly other South American primate lineages; and (iii) suggest that eustatic sea level fall [‘eustatic sea level’ is the distance from the center of Earth to the sea surface; increases in eustatic sea level can be generated by decreasing glaciation, increasing spreading rates of mid-ocean ridges, or creation (upsurging) of more mid-oceanic ridges] that was coincident with the onset of Antarctic glaciation — might have played a role in facilitating transatlantic dispersal of these species.

The Santa Rosa locality is just south of the border between Perú and Brazil, so it’s in Perú. This locality has (mysteriously) previously yielded: a single upper molar of a possible stem platyrrhine (Perupithecus); fragmentary teeth of an unnamed second anthropoid taxon; numerous isolated teeth and maxillary and mandibular fragments of caviomorph rodents and marsupials; and rare remains of bats, noto-ungulates, and enigmatic mammals of Afro-Arabian origin.

Bayesian clock–based phylogenetic analysis [‘Bayesian inference of phylogeny’ uses a likelihood function (integration of Markov chain Monte Carolo algorithms) to create a quantity called the posterior probability of trees — using a model of evolution, based on various probabilities, producing the most likely phylogenetic tree for the given data] nests this genus (Ucayalipithecus) deep within the otherwise Afro-Arabian clade Parapithecoidea and indicates that transatlantic rafting of the lineage leading to Ucayalipithecus likely took place between ~35 and ~32 million years ago — a dispersal window that includes a major worldwide drop in sea level that is known to have occurred near the Eocene-Oligocene boundary. 😊


Science 10 Apr 2020; 368: 194-197 & editorial pp 136-137

COMMENT:David, the most amazing portion of this story is that these “precursors of rodents” and “precursors of marsupials” also joined the primate precursors on these trips. Sounds like a story right out of (a precursor version of) Noah’s Ark. 😉

And I see the book is available on and also available for anyone’s Kindle.

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