The diversity of animal morphology has evolved through evolutionary changes in embryonic
development. How do the rules of development define what morphologies are available for natural selection to act on? How does natural selection tweak morphology within these rules and how, then, do novel structures evolve? My current work explores the answers to these questions in two structures: the mammalian tail and the avian vocal tract. Although many of the molecular pathways controlling vertebrate segmentation during normal development are understood, the genetic and developmental underpinnings of the tremendous variation in size and number of vertebrae are mostly unknown. Using naturally occurring tail length variation in the deer mouse, Peromyscus maniculatus, we integrate phylogeography, genetic mapping, and embryological data to explore the evolutionary, genetic, and developmental mechanisms influencing adaptive variation of the vertebral column among populations of a single species. Over longer evolutionary time scales, development can evolve to produce seemingly novel organs. A prime example of an organ with no obvious homology to existing structures is the source of vocalization in birds, the syrinx. The apparent lack of larynx-syrinx homology and the unique anatomical location of the syrinx at the junction of the trachea and bronchi imply several questions regarding the evolution of novel structures and the evolution of developmental patterning mechanisms. We combine in ovo transplants, in silico modeling, and comparative gene expression studies to explore how the development of the tetrapod airway was modified along the avian lineage to produce a new vocal organ. Together, these studies provide insight into the evolution of developmental change across vastly different tissues and time scales.