Fossils of a 13-million-year-old extinct gavialoid crocodilian from the Peruvian Amazon suggest that South American and Indian gavialoids evolved separately to acquire protruding, ‘telescoped’ eyes, according to an international team of paleontologists from France, Peru and the United States.
The skull of Gryposuchus pachakamue, a proto-Amazonian gavialoid from the Miocene lakes and swamps of the Pebas Mega-Wetland System, in dorsal, ventral, and lateral view. Scale bar – 5 cm. Image credit: Salas-Gismondi R. et al.
The team’s study, published online in the journal PLoS ONE, provides a long-sought insight about gavialoids — a diversified group of mostly extinct long-snouted crocodilian species — that are represented today by just one living species, the Indian gharial (Gavialis gangeticus).
The scientists, led by Dr. Rodolfo Salas-Gismondi from the University of Montpellier in France and the Natural History Museum in Peru, examined fossils from the 13-million-year-old (Miocene epoch) gavialoid crocodilian, the oldest known gavialoid from the Amazon.
They named the new species Gryposuchus pachakamue after Pachakamue, a pre-Hispanic South American storyteller god thought to have knowledge about the origins of South American life.
The fossils came from the Pebas Formation in northeastern Peru, which was likely made up of swampy waterways, suggesting that the crocodilian had a river-dwelling lifestyle. It had only slightly telescoped eyes.
“Gryposuchus pachakamue was distinct from all the other crocodiles living in the vast Pebas Mega-Wetlands of northern South America,” Dr. Salas-Gismondi said.
“It was the only long-snouted species within a hyper-diverse crocodile community dominated by blunt-snouted, clam-eating caimans.”
Time calibrated phylogenetic tree of the Gavialoidea and relevant paleogeographic distributions associated with the evolution and diversification of gavialoids in marine and freshwater settings. During the Late Paleocene-Early Eocene interval, peaks of sea surface temperature (SST) and global sea surface level (GSL) occurred together with tropical marine connections through the Tethys Ocean and Caribbean Sea. During the Neogene, distinct biomes dominated tropical South America: (A) Acre Phase, after the onset of the eastern-draining Amazon and northward-draining Orinoco river systems; and (B) Pebas Mega-Wetland System, with its drainage northward to the Caribbean Sea. Abbreviations: Olig. – Oligocene, Ple. – Pleistocene, Pli. – Pliocene. Image credit: Salas-Gismondi R. et al.
Dr. Salas-Gismondi and his colleagues conducted phylogenetic and morphometric analysis to assess the likely evolutionary development of the protruding telescoped eyes of Indian and South American species.
Their analysis suggested that Gryposuchus pachakamue represents the ancestral condition from which the South American lineage evolved telescoped eyes.
The eyes therefore evolved in parallel in South American and Indian lineages, at first showing partial telescoping as in Gryposuchus pachakamue, and eventually becoming fully telescoped as seen in later-evolving species.
Both South American and Indian gavialoids adopted a river-dwelling lifestyle, and it is likely that telescoped eyes were adaptive, helping them to catch fish in these habitats.
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Salas-Gismondi R. et al. 2016. A New 13 Million Year Old Gavialoid Crocodylian from Proto-Amazonian Mega-Wetlands Reveals Parallel Evolutionary Trends in Skull Shape Linked to Longirostry. PLoS ONE 11 (4): e0152453; doi: 10.1371/journal.pone.0152453
