PERMANOVA results from Principal component analysis of avian hind limb and foot morphometrics and the relationship between ecology and phylogeny

Principal component analysis has been used to test for similarities in
ecology and life habit between modern and fossil birds, however, the two
main portions of the hindlimb—the foot and the long bone elements—have not
been examined separately. We examine the potential links between
morphology, ecology, and phylogeny through a synthesis of phylogenetic
paleoecological methods and morphospace analysis. Both hindlimb
morphologies and species’ ecologies exhibit extreme phylogenetic clumping,
although these patterns are at least partially explainable by a Brownian
motion style of evolution. Some morphologies are strongly correlated with
particular ecologies, while some ecologies are occupied by a variety of
morphologies. Within the morphospace analyses, the length of the hallux
(toe I) is the most defining characteristic of the entire hindlimb. The
foot and hindlimb are represented on different axes when all measurements
are considered in an analysis, suggesting that these structures undergo
morphological change separately from each other. Early birds tend to
cluster together, representing an unspecialized basal foot morphotype and
a hindlimb reliant on hip-driven, not knee-driven, locomotion. Direct
links between morphology, ecology, and phylogeny are unclear and
complicated, and may be biased due to sample size (~60 species). This
study should be treated as a preliminary analysis that further studies,
especially those examining the vast diversity of modern birds, can build
upon.