Gnatusuchus

Gnatusuchus is an extinct genus of caiman represented by the type species Gnatusuchus pebasensis from the Middle Miocene of Peru. Gnatusuchus lived about 13 million years ago (Ma) in a large wetland system called the Pebas mega-wetlands that covered over one million square kilometers of what is now the Amazon Basin (the modern basin had not yet developed at that time and instead of draining from west to east into the Atlantic Ocean, river systems drained northward through the wetlands and into the Caribbean Sea). Gnatusuchus likely fed on bivalves in oxygen-poor marsh and swamp environments, using blunt teeth to crush their thick shells. Gnatusuchus has a short, rounded snout and shovel-shaped lower jaw, which may have been adaptations for feeding on these bivalves. The teeth at the back of the jaws are large and globular-shaped whereas the front teeth are more peg-like. Gnatusuchus has only 11 pairs of teeth in its lower jaws, far fewer than in most other crocodylians. Based on the size of the skull material, the estimated total body length of Gnatusuchus is 148.9 to 167.7 centimetres (4.89 to 5.50 ft).

G. pebasensis was named in 2015 on the basis of a nearly complete skull and several lower jaws from the Pebas Formation near Iquitos in Peru. It lived alongside six other species of crocodylians, including two other caimans with crushing dentitions: Kuttanacaiman iquitosensis and Caiman wannlangstoni. The genus name comes from the Quechua word ñatu meaning "small nose" and the species name comes from an Amazonian village called Pebas. A phylogenetic analysis published alongside its initial description placed Gnatusuchus as the most basal member of the clade Caimaninae. Two other caimanines with crushing dentitions, Kuttanacaiman and Globidentosuchus, were also found to be basal caimanines, suggesting that a specialized crushing dentition was ancestral to the group. Later caimanines, including most modern species, have more generalized dentitions, although a few derived species such as C. wannlangstoni seem to have reacquired crushing teeth. Below is a cladogram from that analysis with crushing-type species in bold: