Paleontologists Gain New Insight to "Telescoping" Crocodile Eyes

by AMNH on

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Fossils of a 13-million-year-old extinct crocodilian from the Peruvian Amazon suggest that South American and Indian species of crocodiles evolved separately to acquire protruding, “telescoped” eyes that helped the animals conceal themselves underwater while scanning the banks of rivers and lakes for prey. 

Gryposuchus pachakamue
Photographs of the almost complete skull of the newly discovered extinct Amazonian gavialoid crocodillian, Gryposuchus pachakamue.

The new study, published in the journal PLOS ONE, provides a long-sought insight about the extremely long and slender-snouted gavialoids—one of the three major types of crocodilians, along with alligators and crocodiles—that are represented today by just one living species, the Indian gharial.

“The extraordinarily well-preserved fossils of this new 13-million-year-old gharial document how independent, parallel evolution of long-snouted animals with specialized visual systems occurred across continents,” said John Flynn, Frick Curator of Fossil Mammals in the Museum's Division of Paleontology and an author on the paper.

The head of a swimming Asian crocodilian with a long, thin snout viewed in profile.
The Indian gharial is the only modern example of the crocodilian family Gavialidae.
Wikimedia Commons

Known for their elongated, narrow snouts, and sharp, piercing teeth, gavialoids are a diverse group of mostly extinct crocodilians that lived in an array of tropical regions including in South America and India. Fossils of gavialoid crocodilians from South America and the modern Indian gharial have similar telescoped eyes, but it was not known how these features evolved.

Flynn has been co-leading prospecting and collecting expeditions in Peru's Pebas Formation for more than a decade, uncovering fossils including a hyper-diverse assemblage of at least seven different species of crocodilians in the Amazon bone bed. Among these extraordinary fossils, the researchers found Gryposuchus pachakamue, the oldest-known gavialoid crocodilian from the Amazon. The area where the researchers discovered the new gavialoid once contained a massive wetland system, suggesting that the early gharial had a lake-dwelling lifestyle.

Excavating Mandible
Members of the international expedition team collecting a Gryposuchus pachakamue mandible.
©D. De Franceschi

Gryposuchus pachakamue was distinct from all the other crocodiles living in the vast Pebas Mega-Wetlands of northern South America,” said Rodolfo Salas-Gismondi of the University of Montpellier in France and the Natural History Museum in Lima, Peru, and the lead author of the study. “This new gavialoid was the only long-snouted species within a hyper-diverse crocodile community dominated by blunt-snouted, clam-eating caimans.”

The new analysis suggests that Gryposuchus pachakamue represents the ancestral condition from which the South American lineage evolved protruding eyes. This means that the distinctive eyes of gavialoids evolved in parallel in South American and Indian groups, eventually becoming fully telescoped during the evolution of other members of the lineage. 

Learn more about Crocs: Ancient Predators in a Modern World, which opens on May 28.