Procrustes analysis: a tool to understand shape changes of the humerus in turtles (Chelonii)

The aim of this paper is to study the effects of locomotor adaptations to a particular environment on the structure of an important element of the appendicular system, the humerus. The variation of the humerus shape pattern is quantified and statistically studied using geometric morphometry, from a sample of 122 humeri belonging to 69 species of extant and extinct turtles. The calculation of a multivariate regression reveals that the shape is strongly correlated with a specialization to aquatic habitat. A parallelism between shape patterns of the humerus, types of limbs coordination and aquatic strategies of life is discussed for groups of highly aquatic freshwater turtles and sea turtles.