A preliminary study on the ornamentation patterns of ganoid scales in some mesozoic actinopterygian fishes

Ganoid scales are one of the most common remains of vertebrates in the fossil record of Paleozoic and Mesozoic. Their knowledge is important for the understanding of the paleobiology and evolution of actinopterygian fishes. The distinctive feature of these scales is the outermost shiny layer of ganoine, an hyper-mineralized enamel-like tissue. During the Mesozoic, ganoid scales show a great variety of shapes and very different patterns of ornamentation made of ganoine. The surface of scales may be from smooth to very ornamented, with a relief arranged in tubercles, ridges, grooves or a combination of them. Here we present a preliminary study on the squamation of some Mesozoic non-teleost actinopterygians in order to test the association between body shape and ganoine ornamentation. Using several morphological descriptors, we built an empirical morphospace to compare ganoid scales ornamentation. The use of a quantitative method to describe scales allows to test if there is a meaningful correlation between body shape and ganoine ornamentation in non-teleost actinopterygians. We found an important association between body shape and scale ornamentation in the taxa under investigation. In particular, deep-bodied fishes bear a more complex and variegate ornamentation than fusiform ones. This finding has important implications in our understanding of non-teleost actinopterygians paleobiology. Since swimming activity is a primary function for fish and this is performed by the body acting as an integrated unit, the correlation between body shape and ganoine ornamentation could be related to hydrodynamics. A quantitative test of this hypothesis, however, would be desirable.