Crocodilians – a group including alligators, crocodiles and their relatives – have collectively thrived since the dinosaur days, but species arise and vanish as their environments change. A 13-million-year-old crocodilian fossil trove of unprecedented diversity, found near Iquitos in the Peruvian Amazon, reflects the ecology of a very different landscape. An international team of researchers published the findings on February 25 in the journal Proceedings of the Royal Society.
Seven species, five brand new to science, were extracted from two lignite outcroppings in the Amazon digging site. Except for a gavialoid (one of three categories of crocodilians, of which only one species is extant) , all were caimans, close relatives of alligators which populate South America today. The previously discovered species included Purussaurus neivensis – with sharp teeth and powerful jaws for catching any animal – and a “duck-faced” Mourasuchus atopus – with a broad, flat snout and sharp little teeth which may have specialized in eating small fish. The first fossil found belonged to a smooth-fronted caiman (Paleosuchus trigonatus), a much smaller generalist predator which still inhabits the region.
The study focuses largely on three new species: Gnatusuchus pebasensis, Caiman wannlangstoni, and Kuttanocaiman iquitosensis. All have short, shovel-shaped snouts and thick, blunt teeth. The authors, led by Rodolfo Salas-Gismondi of the University of Montepellier, proposes that they specialized in eating clams and other mollusks excavated from muddy lake-beds with their snouts. Many of the site’s abundant mollusk shells – thick, rugged shells adapted to withstand predators – had been distinctively broken or scarred by crushing forces, and many of these caimans’ teeth were correspondingly worn down.
The dig site is remarkable in several ways. Such a great number of crocodilian species had never been found coexisting in any living or fossilized community; by contrast, no more than three of the Amazon’s six living caiman species inhabit a given area today. Nearly all known types of crocodilian snouts are represented. Furthermore, it reveals the first shell-crushing caimans, similar to alligators from the Cretaceous. A phylogenetic analysis suggests that all caimans, now sharp-toothed generalists, may have evolved from them.
These creatures of the Middle Miocene Epoch lived in a vast “mega-wetland” of swamps, rivers, lakes, and bays. Many lakes were low in oxygen, giving mollusk-eating caimans little competition from aquatic predators such as fish and crustaceans. About 2.5 million years later, the growing Andes reshaped the terrain into three river systems which now sprawl across northern South America. As displayed in fossils from the region, mollusks declined and shell-crushing caimans were replaced by species better able to prey on the diverse animals of river and rainforest