After a few minutes incubation of broken gastroliths in 5% acetic acid, the large-diameter organic fibers, corresponding to chitin-protein fibers, are well visible on surface (Figure 3A–C). When more decalcified, a complex network of fibers appear showing not only the parallel organic layers previously observed in light microscopy but also cross fibers of similar size (Figure 3D and 3E). This transversal striated structure was already visible in some pictures of Figure 2 (notably in Figure 2A).