Abstract:
First diagnostic fossils of the Late Cretaceous Crocodyliform (Mesoeucrocodylia, Reptilia) from Indo-Pakistan has been discovered from the upper Pab Formation, Vitakri area of Barkhan District, Balochistan, Pakistan. The fossils of Pabwehshi pakistanensis, a Baurusuchids Mesoeucrocodylia consist of well-preserved cranial elements as rostrum (holotype) and two anterior dentaries, axial elements as two isolated and three articulated vertebrae and appendicular elements as distal femur/humerus (referred specimens). The Synapomorphies of Pabwehshi pakistanensis which relates to the Mesoeucrocodylia are; the premaxilla and maxilla meeting along a simple but joint on the lateral aspect of the skull, a bony secondary plate formed by the same two bones and amphicoelous vertebrae. Pabwehshi pakistanensis has relatively deep rostrum, and divided, anterolaterally-facing external nares that exclude Pabwehshi from Neosuchia, which is characterized by a dorsoventrally compressed rostrum and confluent, dorsally facing external nares. Based on diagnostic characters in the rostrum and dentition, the Pabwehshi is referable to Baurusuchidae. Pabwehshi can be differentiated from all other basal Mesoeucrocodylia on the basis of six characters; an elevated first premaxillary alveolus; a prominent roof over the external nares; a diverticulum in the posterodorsal corner of external nares; reduced fourth and fifth dentary teeth; an enlarged caniniform six dentary tooth; and a diastematic fossa positioned just posterior to the second maxillary tooth. The diagnostic features of Pabwehshi pakistanensis also provide information about its phylogenelic evolution. The rostrum of Pabwehshi pakistanensis has a foreshortened anterior snout, with serrated teeth that interlock to form a zig-zag cutting edge. The anterolaterally directed external nares are bordered ventrally and laterally by a well marked narial fossa. Comparisons with Crocodyliforms of equivalent age indicate that the Pabwehshi is a Baurusuchid Mesoeucrocodylian related to Baurusuchus from Brazil and Cyanodontosuchus from Argentina. Pabwehshi pakistanensis is the first Baurusuchid known outside South America. It provides further evidence of a Cretaceous biogeographic link between South America and Indo-Pakistan. Indian Crocodyliforms are known only from teeth and vertebrae that are not diagnostic beyond Crocodyliformes. The present coarse taxonomic identification of Indian fossils offer little clue about Indo-Pakistan`s paleogeographic link with South America but the present discovery from the Late Cretaceous (Maastrichtian) Pub Formation of Balochistan, Pakistan provides a new advantage to assess the evolution of Indo-Pakistani biota. Newly discovered fossils from Vitakri area represent the most diagnostic Crocodyliform remains from the Indo-Pakistan subcontinent and facilitate comparison with other Crocodyliforms especially those from Gondwanan parts such as Africa, South America and Madagascar.
Page(s):
241-259
DOI:
DOI not available
Published:
Journal: Proceedings of 5th Pakistan Geological Congress , Volume: 0, Issue: 0, Year: 2007