Convergence of animal propulsor placement for optimal maneuverability in fluids

Abstract Swimming and flying animals across diverse taxa rely on the ability to maneuver for feeding1-6, escaping predation7-9, finding mates10-13, and navigating complex physical environments14-16. As such, the evolutionary success of these animals depends in part on propulsor designs that can efficiently change the orientation of the body during locomotion. We show that across 292 species of swimming and flying animals—including birds, fish, cetaceans, bats, insects, and sea turtles—the location of lateral maneuvering propulsors is tightly constrained at a location approximately 1/3 of the body length from the anterior end. A theoretical model for optimal turning is consistent with these observations, and it makes a further prediction of a non-trivial relationship between propulsor placement and body center of mass. That prediction is also confirmed by an additional, detailed morphometric analysis of 38 species. The present observations are notable in that a simple physical model appears sufficient to explain observed morphological diversity, and it suggests that propulsor placement in swimming and flying metazoans favors structural solutions that are adapted to enable efficient maneuvering in fluids.