Morphological and compositional analyses of coprolites from the Upper Cretaceous Bauru Group reveal dietary habits of notosuchian fauna

Abstract

The fluvial deposits of the Adamantina Formation (Upper Cretaceous, Bauru Group) have produced a rich fossil vertebrate record of fishes, amphibians, lizards, snakes, turtles, dinosaurs and mammals. However, the record of notosuchians (Crocodylomorpha) is remarkable in terms of both diversity and number of findings. Here, we report a large number of new coprolites found in association with skeletons of crocodylomorphs from the Adamantina Formation in the cities of Jales and Fernandópolis, São Paulo State, Brazil, and discuss their meaning for the understanding of feeding habits of their producers. The coprolites from Jales were found mostly together with adult skeletons of baurusuchids and crocodylomorph egg clutches, while the coprolites from Fernandópolis are associated with adult sphagesaurids and juvenile and adult baurusuchid skeletons, and rare crocodylomorph egg clutches. Forty-one coprolites were analysed encompassing different degrees of preservation. The X-ray diffraction showed the coprolites are comprised mainly of fluorapatite. The presence of bone fragments in some coprolites, together with their typical crocodylomorph cylindrical shape with rounded ends, strongly indicates that Baurusuchidae not only are carnivores, but that also ingested large bone fragments. On the other hand, the coprolites assigned to Sphagesauridae generally show a more complex chemical composition and present plant remains within which indicate this group, at least in part, fed on plants. Our results reinforce the importance of these ichnofossils as an independent source of information on the feeding habits of their producers and add new evidence these two groups of crocodylomorphs fed on different food sources.