Morphology and allometry suggest multiple origins of rostral appendages in <scp>S</scp>ri Lankan agamid lizards

Abstract

Abstract Rostral appendages occur in a very small number of species spread across the entire clade of iguanian lizards. The five species of S ri L ankan agamid lizards of the poorly known endemic genus C eratophora show remarkable variation in the morphology and development of rostral appendages, which are absent in two species and present in the other three. Parsimony and B ayesian comparative methods do not robustly resolve whether the appendage evolved once (with two losses), twice (with one loss) or thrice independently. The appendage in C . tennentii is leaf‐shaped, present in juveniles and monomorphic in adults. It is quite dissimilar to the appendages in C . aspera and C . stoddartii which are horn‐shaped, absent in juveniles and dimorphic in adults. C eratophora stoddartii is more closely related to C . erdeleni , which lacks the rostral appendage, than it is to C . aspera . The combined morphological, allometric and phylogenetic evidence suggests rostral appendages evolved three times within C eratophora : perhaps once as a result of natural selection for crypsis (in C . tennentii ) and twice as a result of sexual selection (in C . aspera and C . stoddartii ). Our results suggest that these unusual ornaments can evolve by more than one mechanism and more readily than is suggested by their low frequency among iguanian lizards.