New insights into the origins of Amazonian biodiversity

A team from ISEM (University of Montpellier, IRD, CNRS), in partnership with Géosciences-Environnement Toulouse (Université Paul Sabatier /CNRS/IRD) and the Natural History Museum of Lima (Peru), has used a 13-million-year-old deposit found in Peruvian Amazonia, which includes 7 species of fossil crocodiles, to shed light on the origin of the exuberant Amazonian biodiversity.
These results have just been published in the journal Proceedings of the royal society b.

An unexpected discovery

Gnatusuchus pebasensis - Credit: Kevin Montalbán-Rivera

Since 2002, this international team has been prospecting in northeastern Peru, mining fossiliferous levels dating back to the Miocene epoch.
"Only fossils allow us to better understand how the Amazon ecosystem emerged and how it functioned in the past. And these fossils, particularly of vertebrates, are extremely rare! In such appalling field conditions, discovering such a deposit is a real tour de force," explains Pierre-Olivier Antoine, Professor of Paleontology at the University of Montpellier and co-author of the article.
"Every time such a window on the past opens, it provides totally new data on these ecosystems of the past. And what we find is rarely what we expected to find," says John Flynn, co-author of the paper and Curator of Fossil Mammals at the American Museum of Natural History in New York.

Hyperdiversity linked to unexpected diets

The overabundance of crocodile species discovered in the deposit is probably due to the use of an unusual food resource for present-day crocodiles: shellfish (such as clams, mussels and whelks). Indeed, of the seven crocodile species described in the article, three of them, totally new to science, probably ate shellfish. The strangest is Gnatusuchus pebasensis, a small duck-billed caiman with globular teeth, which probably used its open mouth to stir up the muddy bottom of waterholes and munch on clams and other shellfish...
" When we analyzed the skull and jaws of Gnatusuchus and deduced that it crunched shellfish using platypus-like lateral head movements, we immediately realized that this was an exceptional animal", recalls the article's first author, Rodolfo Salas-Gismondi, Director of the Paleontology Department at the Natural History Museum in Lima and doctoral student at the Institut des Sciences de l'Evolution de Montpellier (University of Montpellier / IRD / CNRS).
Associated with shellfish-eating caimans, the researchers also discovered the first fossil representative of today's Amazonian caiman, with a longer, narrower mouth adapted to more conventional prey.

Study partners :

  • Patrice Baby of the Institut de Research pour le Développement (Géosciences-Environnement Toulouse, Université Paul Sabatier /CNRS/IRD)
  • Julia Tejada-Lara of the Natural History Museum in Lima (Peru) and the University of Florida in Gainesville
  • Frank Wesselingh of the Naturalis Biodiversity Center in Leiden (Netherlands)

The study was funded by NASA, the Field Museum (Chicago), the American Museum of Natural History (Frick Fund, New York), the ECLIPSE II Program, the Centre National de la Research Scientifique and the Institut de Research pour le Développement.

Researchers' contact details :