Mammals evolved from a reptile-like ancestor that used its limbs and tail together for walking and running. In early mammals, however, the limbs moved independently from the tail. This allowed mammal tails to evolve entirely new functions or to disappear in species like humans and other apes. Mammal tails play essential roles in movement, social interaction, energy storage, and protection. These many functions are enabled by variation in the shape, size, and number of individual vertebrae. Yet, little is known about how such variety arose during mammal evolution, how different tails develop from embryo to adult, or how different bone-tendon-muscle connections determine how a tail is used. This interdisciplinary research program will answer these questions and provide training for students and postdoctoral fellows across three laboratories. The research will also inspire an interactive exhibit in collaboration with the University of Michigan Natural History Museum. This exhibit will include 3-D printed mammal tails, representing both real and imaginary forms, strung with cables that will allow visitors to explore how tails function. In doing so, visitors will gain an intuitive understanding of how changes in tail anatomy favor specific uses. This collaborative proposal leverages over ten years of synergy among the research team members, combining insights from phylogenetic comparative models, evolutionary developmental biology, and biomechanics. In Aim 1, a broad survey of