Integrative experimental approaches to adaptive interpretations of the fossil record

In vivo analyses facilitate a direct knowledge of how a feature or anatomical complex is used during an organism's lifetime, information critically important for increasing the efficacy of comparative studies of living and fossil taxa. In the mammalian skull, dietary properties have a pronounced influence on the ontogeny of the masticatory apparatus. Diet‐related variation in loading levels induces a cascade of changes at the gross, tissue, cellular, protein and genetic levels, with such tissue modeling and remodeling maintaining the integrity of oral structures. Ongoing integrative research using a rabbit model of long‐term dietary plasticity in jaw joints offers unique insight into the caveats or limits on morphological inference that apply to functional interpretations of fossil remains. First, as the fossil record consists primarily of bony elements, analyses that fail to account for the disparity in the hierarchical network of responses of hard vs. soft tissues may considerably overestimate the adaptive signal based on phenotypic differences between morphs. Second, the developmental onset and duration of a loading stimulus associated with a given feeding behavior can impart a considerable effect on patterns of intraspecific variation that can mirror differences observed between taxa. Marked variation in joint form, and even joint function, can also characterize adult conspecifics that differ in age.