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Innovations in foraging behavior can drive morphological diversity by
opening up new ways of interacting with the environment, or limit
diversity through functional constraints associated with different
foraging behaviors. Several classic examples of adaptive radiations in
birds show increased variation in ecologically relevant traits. However,
these cases primarily focus on geographically narrow adaptive radiations,
consider only morphological evolution without a biomechanical approach, or
do not investigate tradeoffs with other non-focal traits that might be
affected by use of different foraging habitats. Here, we use X-ray
micro-computed tomography (microCT), biomechanical modelling, and
multivariate comparative methods to explore the interplay between foraging
behavior and cranial morphology in kingfishers, a global radiation of
birds with variable beaks and foraging behaviors, including the archetypal
plunge-dive into water. Our results quantify covariation between the shape
of the outer keratin covering (rhamphotheca) and the inner skeletal core
of the beak, as well as highlight distinct patterns of morphospace
occupation for different foraging behaviors and considerable rate
variation among these skull regions. We anticipate these findings will
have implications for inferring beak shapes in fossil taxa and inform
biomimetic design of novel impact-reducing structures.
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