My research program is firmly rooted in comparative anatomy as an experimental science that creates natural experiments to answer specific functional and evolutionary questions. At a basic level, it seeks to understand how complex systems can evolve further while remaining functional at all stages. My overarching working hypothesis posits that seemingly large changes during macroevolutionary processes are actually the result of relatively small changes that fundamentally affect the construction and, thus, the functioning of an organism. My research group is working on a variety of vertebrate model species from lampreys to sharks, and from alligators, birds, and mammals to human beings.

Our research program explores the functional morphology and evolution of complex systems by discovering and analyzing structures and constructional principles, and by developing theoretical concepts. Examples of our discoveries are the special construction of the avian hyoid suspension and its implication for the evolution of feeding adaptations in birds and mammals; the fundamental roles of a kinetic larynx, air sacs, and the skin in avian vocalization; the mechanical role of cutaneous fat for the movement of contour feathers; the function of the depressor feather muscles and its significance for the evolution of birds and avian flight; the impossibility of feathers evolving from the scaly integument of dinosaurs; methods of biomechanical analysis, modeling, and animation of complex skeleto-muscular systems based on CT and MRI data; the role of the human shoulder suspension apparatus in the successful global invasion by hominins; the evolution of the shoulder suspension apparatus of bipedal humans from a head suspension apparatus of quadrupedal mammals; and the postulate that systematics and comparative anatomy are based on fundamentally distinct research programs.

All our research projects are tied to our fundamental interest in the reconstruction of macroevolutionary changes as a result of individual variation and natural selection by synthesizing functional-morphological and behavioral-ecological data of extant organisms with paleoclimatological and geological data. An example is my long-term study of the feeding and drinking behavior, functional morphology, ecology, and evolutionary history of the Psittaciformes (i.e., cockatoos and parrots), which has also implications for the evolution of the Gondwanan avifauna in general.