Gond. Geol. Magz., Spl. V. 8, April, 2005. pp. 101-109 A Sauropod Braincase from the Pab Formation (Upper Cretaceous, Maastrichtian) of Balochistan, Pakistan Jeffrey A. Wilson12, M. Sadiq Malkani , and Philip D. Gingerich1 Abstract Pakistan during that interval. However, the Mesozoic and Cenozoic vertebrate fossils of Indo-Pakistan are Recent geological and paleontological exploration best known from Permian to Lower Jurassic sediments in the Pab Formation (Upper Cretaceous) of of India predating the transition (Jain, 1980; Balochistan Province has uncovered new terrestrial Bandyopadhyay and Sengupta, 1999; Ray and vertebrate remains. Together with Cretaceous Bandyopadhyay, 2003) and Eocene to Miocene vertebrates from India, the Pab vertebrates provide information about the paleobiogeographic history of sediments of India and Pakistan postdating the transition Indo-Pakistan during its northward migration towards (e.g., Gingerich and Wells, 1983; Barry et al., 1995; Asia. Vertebrate remains collected from several Gingerich et al., 2001; Verma et al., 2002). localities in the Pab Formation include numerous, Until recently, Mesozoic transitional faunas were isolated postcranial bones attributable to titanosaur recorded only from uppermost Cretaceous sediments of sauropods and a well-preserved sauropod braincase that central and western India (Fig. 1), which produce is described here. numerous but often disarticulated remains (e.g., Rana, The Pab braincase is referable to Eusauropoda, but 1990; Sahni and Bajpai, 1991; Prasad and Rage, 1991, it does not preserve characteristics diagnostic of lower- 1995; Loyal et al., 1996; Prasad and de Broin, 2002; level sauropod clades. The Pab braincase is relatively Rana and Wilson, 2003). Few Upper Cretaceous Indian small and diagnosed by a prominent supraoccipital vertebrates are known from material whose association wedge, pronounced proatlantal facets, and a ventrally is documented. These include the titanosaur sauropod deflected occipital condyle that forms a 120° angle with Isisaurus colberti (Jain and Bandyopadhyay, 1997), the the skull roof. Sauropod braincase material collected abelisaurid theropod Rajasaurus narmadensis (Wilson from Lameta Formation localities in India (Bara Simla, et al., 2003), and an unnamed snake (Mohabey, 1987). Dongargaon) closely resembles the Pab braincase in Recently discovered vertebrate remains from the size and general morphology and shares one or more of Upper Cretaceous Pab Formation of Balochistan, its diagnostic features. The Indian and Pakistani Pakistan (Fig. 1) offer a second opportunity to record braincases likely represent the same genus or species, late Mesozoic transitional faunas of Indo-Pakistan which was distributed across Indo-Pakistan during the (Malkani and Anwar, 2000; Malkani et al., 2001). Pab Cretaceous. Further exploration in both countries will vertebrate fossils include the only diagnostic better constrain the distribution of these and other crocodylomorph from the Mesozoic of Indo-Pakistan vertebrate fossils, providing a clearer picture of the (Pabwehshi; Wilson et al., 2001) as well as numerous, Cretaceous vertebrate fauna of Indo-Pakistan. isolated sauropod elements that include a well-preserved braincase (Malkani et al., 2001). The Pab sauropod Introduction braincase is described here and compared to sauropod Upper Mesozoic and Lower Cenozoic sediments of braincases collected from India. Several derived Indo-Pakistan record its geographical transition from an similarities suggest that the Pab braincase is very similar early connection to greater Gondwana, through a to remains collected from central India. Other sauropod northern drift across the equator, to a later connection to elements from the Pab Formation share autapomorphic Asia. All competing reconstructions of this geogra- features with Indian material, suggesting paleobiogeo- phical transition posit major changes in latitude and graphic continuity across Indo-Pakistan. land connections that likely had a major impact on the terrestrial vertebrate lineages that evolved in Indo- Institutional Abbrevations 1 ISI — Indian Statistical Institute, Kolkata Museum of Paleontology and Department of Geological Sciences, GSI — Geological Survey of India, Kolkata University of Michigan, 1109 Geddes Road, Ann Arbor, Michigan- 48109-1079, U.S.A. GSP — Geological Survey of Pakistan, Quetta UMMP — University of Michigan Museum of 2Geological Survey of Pakistan, P.O. Box 15, Sariab Road, Quetta, Pakistan. Paleontology, Ann Arbor. 102 Jeffrey A. Wilson and Others 500 km Fig.-1. Map showing the location of Upper Cretaceous fossil-bearing outcrops (gray boxes) in India (Lameta Formation) and Pakistan (Pab Formation). Capital cities (Islamabad, Delhi) and location of headquarters of the Geological Survey of Pakistan (Quetta) and Geological Survey of India (Kolkata) are shown. Systematic Paleontology (Nagappa, 1959; Jones et al., 1960; Kazmi and Jan, 1997; Sultan, 1997). DINOSAURIA Owen 1842 The Pab Formation is overlain unconformably by the SAUROPODA Marsh 1877 Paleocene Khadro Formation and is exposed, with the EUSAUROPODA Upchurch 1995 Paleocene Rakhi Gaj and Dungan Formations, in a Figure 2 series of roughly east-west trending en echelon folds Referred specimen : GSP-UM 7000, an isolated near Vitakri. These tectonic structures are thought to braincase that includes elements of the skull roof have been produced by the oblique collision of the Indo- (frontal, parietal) and basicranium (supraoccipital, Pakistan Plate and the Afghan block (Kazmi and Jan, exoccipital-opisthotic, basioccipital, basisphenoid, 1997). The Pab Formation forms the axis of the three prootic, laterosphenoid, orbitosphenoid). A cast of the main anticlines in the region: the Vitakri, Andari- specimen is housed in the University of Michigan Dhaola, Siah Koh anticlines. Thus far 18 vertebrate Museum of Paleontology (UMMP 11303). localities have been sampled in the Vitakri and the Type locality : Vitakri Locality 16. Part of a 15-20 km Andari-Dhaola anticlines. No sample has been exposure of Pab Formation in the Dhaola range, near collected in situ at any of these localities, so the exact the village of Vitakri in eastern Balochistan Province, fossil-bearing horizon is not yet known. Pakistan. Description : The braincase is well preserved but lacks Formation, age, and distribution : The Pab Formation the distal ends of the paroccipital processes, basal is exposed in two widely separated areas of eastern tubera, and basipterygoid processes, as well as the Balochistan: the Pab and Kirthar ranges bordering Sind anterior portions of the orbitosphenoids and latero- in the south and the Sulaiman Range bordering Punjab sphenoids. A portion of the skull roof is preserved that in the north (Fig. 1). In the western part of the includes the parietals internal to the supratemporal Sulaiman Province, the formation is marginal marine to openings and the frontals internal to the supratemporal fluvial (Sultan, 1997). The age is considered to be and orbital margins and posterior of the nasal contacts. latest Cretaceous (Maastrichtian) based on stratigraphic The Pab braincase is relatively small (Table-1) but position within a sequence of dated formations sutures are tightly fused or indistingui- shable, which Sauropod Braincase from Pab Formation 103 Fig-2. Stereopairs of the Pab sauropod braincase (GSP-UM 7000) in right lateral (A), dorsal (B), and posterior (C) views. Abbreviations: bo, basioccipital; bs, basisphenoid; bt, basal tubera; eo, exoccipital-opisthotic; f, frontal; fm, foramen magnum; ls, laterosphenoid; os, orbitosphenoid; p, parietal; pa f, proatlantal facet; pr, prootic; so, supraoccipital; st fo, supratemporal fossa. Roman numerals refer to cranial nerve openings. suggests that GSP-UM 7000 represents a mature their contact. As in other sauropods, the frontal-parietal individual. contact is positioned near the contact of the laterosphe- The parietal is a paired midline element that noid and prootic, and it coincides with a diminution of contacts the frontal anteriorly and has ventral contacts skull roof thickness that can be observed in lateral view. with the supraoccipital, exoccipital-opisthotic, prootic, The supratemporal fenestrae are not preserved, but a and laterosphenoid bones. The parietal is exposed on shallow depression along the frontal-parietal suture, the dorsal and posterior surfaces of the skull and most pronounced on the right side, may represent part of typically participates in the margin of the supratemporal the fossa surrounding it (Fig. 2B). The posterior margin fenestra, which is not preserved in this specimen (Fig. 2 of the skull is marked by low, arcuate ridges formed by B, C). The midline suture of the parietal is partially the parietal on either side of the supraoccipital. The fused, but traces of it can be discerned. The parietal and parietal is well exposed in posterior view, where it frontal are likewise tightly sutured, but a roughened line wraps over the supraoccipital wedge and extends of bone traversing the dorsal skull probably represents laterally to overlay the exoccipital-opisthotic. 104 Jeffrey A. Wilson and Others Table-1 : Principal dimensions of the Pab braincase (GSP- exoccipital-opisthotic or between the two, but this UM 7000) in millimeters. requires confirmation. The occipital condyle is strongly deflected ventrally and forms an angle of approximately Parietals, preserved transverse width 95 120 degrees with the skull roof. This deflection is not Parietals, anteroposterior