Testing for Historical Patterns of Change a Case Study with Frog Pectoral Girdles

Evolutionary morphologists and paleontologists have long questioned whether there are general historical patterns to the distribution of morphological types. Few studies have rigorously addressed that question. This study tests the decoupling hypothesis, which predicts an increase in the number of morphological constraints with a reduction in the number of independent elements. Eight cases of historical transformation of the epicoracoid cartilages of frogs were selected for analysis. Similar morphological shape changes occurred across the independently derived historical transformations as determined by a triangle analysis of shape. These results support the decoupling hypothesis and indicate that there may be generalized historical pathways of structural change. This finding is important for the development of a predictive theory in evolutionary morphology.