Old vs. young: testing hypotheses for the formation of the Amazon basin

Study uncovers biogeographic evidence supporting the Old Amazon hypothesis for the formation of the Amazon fluvial system

Data resources used via GBIF : 780,843 species occurrences
Ortalis guttata
Ortalis guttata (Spix, 1825) observed near Trinidad, Bolivia by Ruben D. Layme (CC BY-NC 4.0)

Covering eight countries, the Amazon ecosystem represents the largest continuous tract of tropical rainforest in the world. The formation of the Amazon basin rivers is believed to a main contributor to the high biodiversity of the ecosystem.

This study examines the fit of phylogenetic and biogeographic data to two different hypotheses around the timing of the formation of the Amazon fluvial system: the "Old Amazon" (up to 10 million years ago) vs. the "Young Amazon" (around 2.5 million years ago).

Researchers used genetic sequence data for six monophyletic taxa across four animals classes—amphibians, birds, insects and mammals—to reconstruct time-calibrated molecular phylogenies. Using GBIF-mediated occurrences they performed ancestral range inferences, testing different dispersal rates and potential isolation barriers.

Their results show evidence of initial dispersals to the basin ranging from around 16 to 10 million years ago with full taxa coverage between 12 and six million years ago. Not all taxa agreed with the temporal range, but in general the results of the molecular and biogeographical analyses provide support for the "Old Amazon" model.

Méndez-Camacho K, Leon-Alvarado O and Miranda-Esquivel DR (2021) Biogeographic evidence supports the Old Amazon hypothesis for the formation of the Amazon fluvial system. PeerJ. PeerJ 9: e12533. Available at: https://doi.org/10.7717/peerj.12533