Who ate whom? Paleoecology revealed through synchrotron microtomography of coprolites (fossil feces)

Abstract: Fossil droppings, known as coprolites, are being increasingly recognized as a valuable source of paleoecological information with special regard to diets, parasitism, and physiology of extinct taxa. Here, it is suggested that the excellent preservation and amount of inclusions in the coprolites (e.g. food residues and parasites) qualifies them as Lagerstätten – deposits with exceptional paleontological information. However, two interlinked problems commonly arise when they are studied. Firstly, it is often difficult to tie coprolites to producers and, secondly, it is challenging to recognize the fragmented and randomly distributed inclusions in their matrix. Here I use propagation phase-contrast synchrotron microtomography (PPC-SRμCT) in combination with other techniques to solve these problems. As a result, the oldest known example of archosaurian osteophagy is uncovered based on inter alia the occurrence of serrated teeth and many crushed bones in coprolites assigned to the Late Triassic theropod-like archosaur Smok wawelski. Osteophagy has previously been thought to be rare among extinct archosaurs with the exception of Late Cretaceous tyrannosaurids. This suggests some degree of ecological convergence between the tyrannosaurids and S. wawelski. Furthermore, exceptionally-preserved beetle remains are discovered in coprolites tentatively assigned to the Triassic dinosauriform Silesaurus opolensis, which had a specialized dentition and possessed beak-shaped jaws that were likely used to peck insects off the ground. Moreover, pterosaur coprolites are shown to contain similar food residues as found in droppings of recent flamingos, implying that some Late Jurassic pterosaurs were filter feeders. I argue that such paleoecological studies have a large impact on our understanding of ancient animals, and that studies of coprolites can unravel parts of ancient food webs in unprecedented ways. Information on past food webs may, in turn, be used to analyze trophic changes through time, which could cast new light on big evolutionary events. This is demonstrated by reconstructing trophic structures in early Mesozoic assemblages that represent snapshots of three stages of early dinosaur evolution.