The taxonomic content of the genus Gavialis from the Siwalik Hills of India and Pakistan

Abstract

The fossil record of the genus Gavialis currently comprises nine species, many of which were erected from the mid nineteenth to the early twentieth century, sometimes on the basis of incomplete specimens. A survey of the Natural History Museum, London, collections, where many specimens were collected in the course of geological surveys in Punjab and Sindh, part of the former Indian Empire, provides a basis to reevaluate the taxonomic content of the genus Gavialis. Four species, G. leptodus, G. pachyrhynchus, G. curvirostris and G. breviceps, are not referable to the genus Gavialis. The species G. hysudricus is considered a junior synonym of G. gangeticus. The genus Gavialis includes two species, namely G. gangeticus and G. bengawanicus; two others, G. browni and G. lewisi require revisions. Several similarities are noted between the tomistomine Rhamphosuchus crassidens and G. leptodus, G. pachyrhynchus, G. curvirostris and G. breviceps. As a generality, the scarcity of information on sampling locations renders difficult a discussion on taxon provenance and age. However, a definitive revision of these taxa requires a revision of R. crassidens as well as an improved stratigraphic framework for all these taxa in a continuing effort to update the diversity of Gavialis and other longirostrine forms in the Mio‐Plio‐Pleistocene of India–Pakistan and SE Asia.

A large crocodyloid from the Oligocene of the Bugti Hills, Pakistan

“…Astorgosuchus bugtiensis was retrieved in the same fluvio-lacustrine deposits as the large tomistomines 'Gavialis' curvirostris and 'Gavialis' breviceps (Pilgrim, 1908;1912;Martin, 2018). Both of the later taxa co-occur with several megaherbivores, such as rhinocerotoids and chalicotheriids among perissodactyls, anthracotheriid artiodactyls and proboscideans (Antoine et al, 2003(Antoine et al, , 2004(Antoine et al, , 2013Métais et al, 2009a;Lihoreau et al, 2017).…”

“…Despite a circular cross section, the crown is heavily worn and no feature of the enamel can be described. Pilgrim (1908Pilgrim ( , 1912 was the first to describe and name several crocodylian species from the Bugti Hills, including a number of longirostrine forms (Martin, 2018). With these remains, Pilgrim (1908) erected Crocodilus bugtiensis, which was later described (Pilgrim, 1912) and…”

An Eocene tomistomine from peninsular Thailand

“…Some taxa are too fragmentary or need revisions. As such, the Siwalik Hills of India and Pakistan contains several taxa previously considered as belonging to the genus Gavialis but instead sharing similarities with tomistomines (Martin, 2018). Also, Ferganosuchus planus was first considered a tomistomine by Efimov (1982) but Jouve (2004) emitted doubt about this identification.…”

“…Aside the early Oligocene Vietnamese occurrence (Böhme et al, 2011), SE Asia does not offer a record for tomstomines. Early Miocene tomistomines might be represented by taxa related to Rhamphosuchus crassidens from the Siwalik Hills of India and Pakistan (Falconer and Cautley, 1840;Head, 2001;Martin, 2018) but their precise stratigraphic distribution and paleoenvironmental context will have to be reevaluated.…”

Revisão filogenética de Alligatoroidea (Crocodylia) e revisão taxonômica das espécies do clado Caimaninae

“…Gavialoidea is formed by marked longirostrine, putatively largely piscivorous forms. While the earliest, most basal gavialoids such as Thoracosaurus were inhabitants of marine and estuarine environments (Brochu, 2003), later, more derived taxa such as the South American clade Gryposuchinae (see Brochu, 2003;Vélez-Juarbe et al, 2007;Salas-Gismondi et al 2016) and fossil forms of the Gavialis genus in South Asia (Martin, 2019) would go on to inhabit full freshwater environments. The only extant gavialoid species, G. gangeticus, which is exclusive of the Indian subcontinent, is a full freshwater taxon (Brochu, 2003).…”