An international team of paleontologists has described three new species of caimans that lived in the swampy waters of what is now northeastern Peru during Miocene, about 13 million years ago.
Kuttanacaiman iquitosensis, left, Caiman wannlangstoni, right, and Gnatusuchus pebasensis. Image credit: © Javier Herbozo.
“The modern Amazon River basin contains the world’s richest biota, but the origins of this extraordinary diversity are really poorly understood,” said team member Dr John Flynn the American Museum of Natural History.
“Because it’s a vast rain forest today, our exposure to rocks – and therefore, also to the fossils those rocks may preserve – is extremely limited.”
Before the Amazon basin had its river, which formed about 10.5 million years ago, it contained a massive wetland system, filled with lakes, embayments, swamps, and rivers that drained northward toward the Caribbean.
Knowing the kind of life that existed at that time is crucial to understanding the history and origins of modern Amazonian biodiversity.
But although invertebrates like mollusks and crustaceans are abundant in Amazonian fossil deposits, evidence of vertebrates other than fish have been very rare.
The fossils of the three newly-identified caiman species – Gnatusuchus pebasensis, Kuttanacaiman iquitosensis, and Caiman wannlangstoni – were recovered from the Pebas Formation in northeastern Peru.
Life reconstruction of the head of Gnatusuchus pebasensis. Image credit: © Kevin Montalban-Rivera / Aldo Benites-Palomino.
The strangest of the three is Gnatusuchus pebasensis, a short-faced caiman with globular teeth that is thought to have used its snout to shovel mud bottoms, digging for clams and other mollusks.
Dr Flynn and his colleagues suggest that the rise of Gnatusuchus pebasensis and other shell-crunching (durophagous) crocs is correlated with a peak in mollusk diversity and numbers, which disappeared when the mega-wetlands transformed into the modern Amazon River drainage system.
“When we analyzed Gnatusuchus bones and realized that it was probably a head-burrowing and shoveling caiman preying on mollusks living in muddy river and swamp bottoms, we knew it was a milestone for understanding proto-Amazonian wetland feeding dynamics,” said Rodolfo Salas-Gismondi, a graduate student at the University of Montpellier, France, who is the first author of the paper published in the journal Proceedings of the Royal Society B.
The scientists suggest that with the inception of the Amazon River System, mollusk populations declined and durophagous crocs went extinct as caimans with a broader palate diversified into the generalist feeders that dominate modern Amazonian ecosystems.
“Today, six species of caimans live in the whole Amazon basin, although only three ever co-exist in the same area and they rarely share the same habitats. This is in large contrast to their ancient relatives, the seven diverse species that lived together in the same place and time,” the scientists said.
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Rodolfo Salas-Gismondi et al. A Miocene hyperdiverse crocodylian community reveals peculiar trophic dynamics in proto-Amazonian mega-wetlands. Proceedings of the Royal Society B, published online February 25, 2015; doi: 10.1098/rspb.2014.2490
