Tuesday, April 26, 2016

[Paleontology • 2016] Gryposuchus pachakamue • A New 13 Million Year Old Gavialoid Crocodylian from Proto-Amazonian Mega-Wetlands Reveals Parallel Evolutionary Trends in Skull Shape Linked to Longirostry

Fig 9. 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 [59,60]. 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. Global and South American schematic paleogeography adapted from Blakey [60] and Hoorn et al. [61], respectively.   DOI: 10.1371/journal.pone.0152453


Gavialoid crocodylians are the archetypal longirostrine archosaurs and, as such, understanding their patterns of evolution is fundamental to recognizing cranial rearrangements and reconstructing adaptive pathways associated with elongation of the rostrum (longirostry). The living Indian gharial Gavialis gangeticus is the sole survivor of the group, thus providing unique evidence on the distinctive biology of its fossil kin. Yet phylogenetic relationships and evolutionary ecology spanning ~70 million-years of longirostrine crocodylian diversification remain unclear. Analysis of cranial anatomy of a new proto-Amazonian gavialoid, Gryposuchus pachakamue sp. nov., from the Miocene lakes and swamps of the Pebas Mega-Wetland System reveals that acquisition of both widely separated and protruding eyes (telescoped orbits) and riverine ecology within South American and Indian gavialoids is the result of parallel evolution. Phylogenetic and morphometric analyses show that, in association with longirostry, circumorbital bone configuration can evolve rapidly for coping with trends in environmental conditions and may reflect shifts in feeding strategy. Our results support a long-term radiation of the South American forms, with taxa occupying either extreme of the gavialoid morphospace showing preferences for coastal marine versus fluvial environments. The early biogeographic history of South American gavialoids was strongly linked to the northward drainage system connecting proto-Amazonian wetlands to the Caribbean region.

Systematic paleontology

Crocodyliformes Hay, 1930 
Eusuchia Huxley, 1875 
Crocodylia Gmelin, 1789 

Gavialoidea Hay, 1930 
Gryposuchinae Vélez-Juarbe et al., 2007 

Gryposuchus Gürich, 1912 

Gryposuchus pachakamue sp. nov.

ZooBank life science identifier (LSID) for species. urn:lsid:zoobank.org:act:6B71903E-9412-44BE-8537-203B07909DEE

Etymology: The Pebasian Gryposuchus species is named after the Quechua word “pachakamue”, primordial pre-Columbian god and first “storyteller” who preserved ancient knowledge about the origin of living things in Amazonia.

Holotype: MUSM 1981, nearly complete skull (Fig 1A–1C).

Locality and Horizon: Locality IQ114, Iquitos area, Peru; Pebas Formation, late Middle Miocene, approx. 13 Ma; Mollusc Zone 8 (MZ8; Fig 1).


Gavialoid history exhibits independent acquisitions of the “telescoped” orbits condition. Analyses of the new Pebasian species Gryposuchus pachakamue and other South American fossil gavialoids document high plasticity in orbital anatomy, which appears to have been strongly correlated with a visually enhanced feeding strategy and environmental circumstances. Morphospaces occupied by fluvial and coastal marine specialists are identified by quantitative analysis of orbital and circumorbital shape variation. In light of the phylogenetic history, a fluvial habitus in South American gharials is derived from ancestral lacustrine-deltaic forms with incipient development of protruding eyes or telescoped orbits. The circumorbital region of coastal marine gavialoids is closer in morphology to that of brevirostrine crocodylians. Identifying morphological steps of parallel evolution and ancestral ecological habitus in gavialoids provides models for reconstructing puzzling phylogenetic histories and adaptive radiations within extinct crocodylomorphs clades with elongated rostrums, such as thalattosuchians, dyrosaurids, and pholidosaurids. Proto-Amazonian connections with the Caribbean Sea to the north, and the subsequent onset of the transcontinental Amazon River System draining eastward, provided multiple habitats and conditions for gavialoid colonizations of new areas and extensive morphological diversification in South America throughout the mid-late Cenozoic.

Rodolfo Salas-Gismondi, John J. Flynn, Patrice Baby, Julia V. Tejada-Lara, Julien Claude and Pierre-Olivier Antoine. 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

13 million-year-old crocodile offers insight into evolution http://ti.me/1U6KyiK via @TIME