Developmental Patterns in Mesozoic Evolution of Mammal Ears

Complex structures with significant biological function can arise multiple times in evolution by common gene patterning and developmental pathways. The mammalian middle ear, with its significant hearing function, is such a complex structure and a key evolutionary innovation. Newly discovered fossils have now shown that the detachment of the ear from the jaw, an important transformation of the middle ear in early mammals, has major homoplasies; the morphogenesis of these homoplasies is also illuminated by new genetic studies of ear development in extant mammals. By extrapolating the developmental morphogenesis of genetic studies into the early mammal fossil record, evolution of the middle ear in early mammals provides an integrated case study of how development has impacted, mechanistically, the transformation of a major structural complex in evolution.