The Early Eocene (~54.5 Ma) Cambay Shale Formation at Vastan lignite mine (Gujarat, India) has yielded remains of both adapoid and omomyoid primates. The collection of primates includes not only jaws and teeth, but numerous exquisitely preserved postcranial elements. We report on the first cranial specimen for a primate from these deposits: an isolated left petrosal that preserves a partial stapes in anatomical position. The petrosal is identified as a primate based on the remnants of a petrosal bulla, and the presence of an ossified tube for the stapedial artery. The specimen documents a posterolateral entry of the internal carotid artery to the middle ear and a lateral course for the promontorial artery across the promontorium, characters most consistent with an attribution to Adapoidea. Of the adapoids published from the Vastan mine, body mass estimates based on the radii of the semicircular canals, calculated from high resolution microCT data, are most in line with previously calculated estimates for Marcgodinotius indicus, so the specimen is provisionally attributed to that species. Preserved anatomy is largely consistent with that described for Cantius. In particular, although the stapedial artery passed through a bony tube, the promontorial artery ran in an open groove from its origin off the internal carotid artery. This contrasts with the condition in omomyoids and most other adapoids, in which the promontorial artery was carried in a bony tube. The identification of an open groove for this artery in Cantius has been somewhat controversial, based on the state of preservation of published specimens. The petrosal from Vastan is extremely well preserved, demonstrating a clear opening in the internal carotid artery bony tube for the exit of the promontorial artery, and a well-demarcated groove on the promontorium for the latter artery that was clearly not enclosed. The absence of a bony tube for the promontorial artery in the oldest known adapoids suggests that the tube arose independently, in parallel, in Omomyoidea and Adapoidea. The promontorial artery is always enclosed in modern haplorhines, but when this artery is retained in living strepsirrhines it is often not fully enclosed by bone. Therefore, the primitive adapoid condition is more similar to that observed in Strepsirrhini. The antiquity and fine quality of preservation of this specimen make it relevant to reconstructing auditory morphology near the base of the primate tree. Grant Information Supported by an NSERC Discovery Grant to MTS and grants from the National Geographic Society and the Leakey Foundation to KDR.
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The youngest time interval of the Cretaceous is known as the Maastrichtian Age, a reference to the strata exposed in the area surrounding the city of Maastricht, in the Netherlands-Belgium border region (Jagt 2001). The stratigraphic succession at the original type-locality of the Maastrichtian (adjacent to the former ENCI quarry, south of Maastricht) only covers the upper part of the Maastrichtian Stage as defined nowadays. However, recent integrated bio- and chemostratigraphic revision by Vellekoop et al. (2022) has shown that in combination with similar lithological sequences at other quarries in the region (e. g., Hallembaye, Curfs), a substantial part of the Maastrichtian Stage is represented. Over the past centuries, the type-Maastrichtian strata have provided a wealth of paleontological data. Despite its importance to the global geological community, most of the quarries in the region have been closed over the last decades. Instrumental quarries such as that of Curfs have already been out of commission for more than a decade, while others, such as the ENCI quarry, were recently closed. Because the soft limestone rocks weather easily and become overgrown rapidly, access to and study of the Maastrichtian rock succession in its type area is becoming very limited. To preserve the geological heritage of this original type-locality of the Maastrichtian, in 2018 we initiated the ‘Maastrichtian Geoheritage Project’. The goal of this project is to preserve the geological heritage of the Maastrichtian type area by (1) digital imagery, using drone photogrammetry and Differential GPS Base & Rover to generate high-resolution and georeferenced 3D models of the most important quarries in the Maastrichtian type region; and (2) archiving rock samples of these quarries for future research. Over the past years, we collected high-resolution (5 cm spacing) reference sample sets from the Hallembaye (2018) and ENCI (2019) quarries, and generated detailed geo-referenced 3D models for both quarries. For the next few years, several other instrumental quarries will be targeted. The acquired sample sets have already spurred a range of stratigraphic, geochemical and paleontological studies (e.g. Vellekoop et al. 2022), including detailed profiles of carbon isotope data and major and trace element concentrations, and many more to come. Moreover, the Maastrichtian Geoheritage Project sample sets will be made available for collaboration with other researchers in the field. Jagt, J.W.M., 2001. The historical stratotype of the Maastrichtian: A review. In: Odin, G.S. (Ed.), The Campanian-Maastrichtian Boundary, pp. 711–722. Elsevier Science B.V. Vellekoop, J. et al. 2022. A new age model and chemostratigraphic framework for the Maastrichtian type area (southeastern Netherlands, northeastern Belgium). Newsletters on Stratigraphy [accepted]
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RBINS Staff Publications 2022 OA
