Data from: Sexual dimorphism, phenotypic integration, and the evolution of head structure in casque-headed lizards

Sexes can differ in features associated with differential reproduction,
which can be used during courtship or aggressive encounters. Some traits
tend to evolve independently between sexes and emerge as sexually
dimorphic within the organismal phenotype. We characterize such a
relationship by estimating the phenotypic integration of the head
morphology and modularity of the crest in the casque-headed lizards
(Corytophanidae). In this clade, some species show extreme sexual
dimorphism (e.g., head crests in the genus Basiliscus) while in others,
both sexes are monomorphic. To characterize these patterns, we define
phenotypic integration at the interspecific level as a pattern or network
of traits evidenced by phylogenetically adjusted correlations that persist
among species. At this level, modularity is an increased connectedness
(e.g., higher correlation) among sections of these networks that persist
in a lineage during the evolution of complex phenotypes. To test both
concepts, we used phylogenetic geomorphometrics to characterize the head
structure of corytophanid lizards, based on a time-calibrated phylogeny
that includes candidate fossil ancestors. We found evidence of an older
diversification of corytophanids than previously reported (~67 vs. ~23.5
MYA) and show that this clade includes two morphological head
architectures: (1) Sexually dimorphic crests present in males that are
evolving independently from the rest of the head structure, and (2) full
integration of the head morphology in monomorphic species. We propose that
both architectures are optimal evolutionary trajectories of the parietal
crest bones in the head of these lizards. In sexually dimorphic species,
these bones are elongated and thinner, and gave rise to the extended crest
used in male courtship displays. In monomorphic species, the parietal
crest grew thicker in both sexes to allow for a better insertion of
muscles associated with a stronger bite.