Niche partitioning, feeding behavior and paleoecology of Caimanines (Crocodyliformes, Crocodylia) from the Miocene of South America based on finite element analysis

Abstract

The fossil Alligatoroid crocodylians of the Caimaninae clade from the Miocene of South America has the largest taxonomic diversity and morphological disparity among the crocodyliforms of the continent during the Cenozoic, considering both fossil and living forms. This record includes fossil forms assigned to living genera, such as Caiman and Melanosuchus, and fossil genera similar to those for being small to medium-sized forms with a presumed generalist habit (Acresuchus and Eocaiman). However, the most notable aspect of the Caimanines of the South American Miocene are the extinct forms that could have hold ecological niches not found between living forms. One of these is the one of potential durophagous predator, assigned to forms such as Gnatusuchus, Globidentosuchus and C. brevirostris. Another one is that of giant top predator, which would be occupied by Purussaurus, which has total body length estimates around 12.5 meters. And another possible ecological niche is the one potentially occupied by Mourasuchus, which has an anteroposterly long, lateromedially broad, dorsoventrally flattened skull and whose feeding habits have been the subject of several hypotheses, most of which differing from the active predator behaviour performed by living forms. As such, the fossil Caimanines from the Miocene of South America exhibit large taxonomic diversity and morphological disparity that suggest a notable niche partitioning. However, the vast majority of the hypotheses on the feeding behavior of these taxa has never been tested from a formal, empirical methodology, which means that there is not yet an understanding about how the possible niche partitioning between these forms was structured. This represents an important gap in our knowledge about these taxa, whose filling constitutes the main objective of this project. Empirical approaches are very important as they can effectively clarify which are the morphological aspects responsible for the feeding and ecological behaviors of these taxa and which morphological and ecological factors may have allowed niche partitioning between the components of that fauna. As such, this project will perform the empirical approaches that can elucidate the most the feeding behaviors of important components of the fauna of fossil Caimanines from the Miocene and South America and thus establish with a good degree of reliability how the niche partitioning between those taxa was structured. These analyses will be performed with one representative of each possible ecological niche: giant top predator (Purussaurus); gulp-feeding predator (Mourasuchus); generalist predator (Acresuchus); and durophagous (C. brevirostris). These approaches will also be performed with living Caimanines (C. latirostris and Melanosuchus niger) for comparative purposes. The analyses are comprised of, firstly, the description of the musculature and associated structures of the adductor chamber that are related with important aspects of the feeding behavior like the maximum gape and jaw opening size, which will provide information on the potential prey of each taxon. Posteriorly, both the reconstructed musculature of the adductor chamber and computed tomography scannings of skulls and mandibles will allow the production of digital models for the performing of the Finite Element Analysis (FEA), which will enable the elucidation of other important aspects related to feeding behavior, such as estimates of bite force. In this way, the performance of these techniques, in a cohesive approach, will provide the necessary empirical analysis to answer the main question of the project. FEA will also be used to elucidate another paleoecological aspect of the South American fossil Caimanines: clarify the possible functions of the hypertrophied eminences ("horns") of Acresuchus and Mourasuchus. In this approach, the analyses will also be performed in living species of Crocodylus that exhibit the structure. (AU)