Changing Modular Patterns in the Carnivoran Pelvic Girdle

Abstract

Patterns of phenotypic integration and modularity provide important clues to understand phenotypic evolution. Here, we investigate patterns of integration and modularity of the pelvic girdle in mammalian carnivorans. Three-dimensional geometric morphometrics was used to test for different modular hypotheses by combining in different ways the four original girdle elements (i.e., ilium, ischium, pubis, and acetabulum). These hypotheses were tested with the complete sample (i.e., order Carnivora) and within families. The hypotheses with more statistical support recognize the four girdle elements as separate modules, with the ischium and pubis more integrated than the ilium and acetabulum. This indicates a strong influence of developmental units in shaping pelvic anatomy. Strikingly, the families Canidae and Ursidae exhibit a different pattern of modularity, showing a modification of the pattern displayed by the whole order, which was attained early in the evolution of the group. Our results indicate that, on long timescales, evolution can change the relationships between structures independently of the developmental patterning, thus overcoming evolutionary constraints.