From 9 million to 5 million years ago the deltas of the Amazonas and the Urumaco, a river on the Gulf of Venezuela that no longer exists, boasted an unparalleled abundance of extremely diverse, highly specialized species of crocodile, researchers from the University of Zurich report.
Writing in the journal Nature Communications, paleontologists Marcelo Sanchez and Torsten Scheyer say a total of 14 crocodile species existed in the region and at least seven of them occupied the same area at the same time.
Venezuela's fossils include all the families of crocodile species that still exist worldwide today, they said.
One of the extinct species was a giant variety that grew up to 40 feet and probably fed on turtles, giant rodents and smaller crocodiles, the researchers said.
"There were no predators back then in South America that could have hunted the three-meter-long [10-foot] turtles or giant rodents. Giant crocodiles occupied this very niche," Scheyer said.
The impressive variety of species in the coastal and brackish water regions of Urumaco and Amazonas became extinct around 5 million years ago, but not from temperature or climate changes. Instead it was caused by a tectonic event, Sanchez said.
"The Andean uplift changed the courses of rivers. As a result, the Amazon River no longer drained into the Caribbean, but the considerably cooler Atlantic Ocean," he said. "With the destruction of the habitat, an entirely new fauna emerged that we know from the Orinoco and Amazon regions today."