Saturday, February 20, 2016

[Paleontology • 2012] Gavialis from the Pleistocene of Thailand and Its Relevance for Drainage Connections from India to Java


Figure 4. Skull and mandible of Gavialis cf. bengawanicus from the Early Pleistocene of Khok Sung (Nakhon Ratchasima Province, Thailand).
A, right lateral view (mirrored for comparison) of DMR-KS-03-25-23. B, line drawing from the left lateral view of the posterior portion of the skull of DMR-KS-201202-1. C, left lateral view of skull of DMR-KS-201202-1. D, E, G, mandible of DMR-KS-201202-1 left lateral (D), occlusal (E), and ventral (G) views. F, incomplete dentaries (DMR-KS-05-06-22-1) in occlusal view; H, detail of the dentition in lateral view as seen on the maxillary fragment DMR-KS-05-03-08-37.
Abbreviations: asan, anterior tip of surangular; asp, anterior tip of splenial; ec, ectopterygoid; exo, exoccipital; fr, frontal; j, jugal; l, lacrimal; ltf, lower temporal fenestra; mx, maxilla; on, otic notch; or, orbit; pfr, prefrontal; po, postorbital; q, quadrate; qj, quadratojugal; sq, squamosal.  || DOI: 10.1371/journal.pone.0044541



Abstract 
Background
The genus Gavialis comprises a single living but endangered species, G. gangeticus, as well as fossil species recorded in the Miocene to Pleistocene deposits of the Indian subcontinent. The genus is also represented in the Pleistocene deposits of Java by the species G. bengawanicus, which was recently recognized to be valid. Surprisingly, no detailed report of the genus exists between these two provinces and the recent evolutionary history of Gavialis is not understood.

Methodology/Principal Findings
We report new material consisting of skull and mandibular remains of Gavialis from the Early Pleistocene of Khok Sung, Nakhon Ratchasima Province, northeastern Thailand. The Gavialis material described herein is attributed to Gavialis cf. bengawanicus and sheds new light on the occurrence of the genus in mainland SE Asia.

Conclusions/Significance
Comparison of this new material with other species referred to the genus Gavialis led us to preliminary restrict the content of the genus to three species, namely G. gangeticus Gmelin, G. bengawanicus Dubois and G. lewisi Lull. The occurrence of G. cf. bengawanicus in Thailand allows us to propose a scenario for the dispersal of Gavialis from Indo-Pakistan to Indonesia, thus bridging a geographical gap between these two provinces. Dispersal by sea appears a less likely possibility than dispersal through fluvial drainages.


Figure 12. Hypothetic dispersal route of Gavialis spp. from their ancestral habitat in Indo-Pakistan toward SE Asia through the East Himalayan syntaxis.
Definitive isolation of Gavialis population is represented by the mountain barriers separating the Salween and Chao Phraya basins and may have taken place during the latest Pliocene–earliest Pleistocene. 1, Ganges Delta; 2, Bhramapoutre Basin; 3, Irrawaddy Basin; 4, Salween Basin; 5, Chao Phraya Basin; 6, Chi and Mun rivers Basin; 7, Mekong Delta. Stars indicate the Early Pleistocene records of Gavialis in SE Asia (Khok Sung, Thailand and Java, Indonesia).

  


Jeremy E. Martin, Eric Buffetaut, Wilailuck Naksri, Komsorn Lauprasert and Julien Claude. 2012. Gavialis from the Pleistocene of Thailand and Its Relevance for Drainage Connections from India to Java. PLoS ONE. 7(9): e44541. DOI: 10.1371/journal.pone.0044541

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