On caudal prehensility and phylogenetic constraint in lizards: The influence of ancestral anatomy on function in Corucia and Furcifer.

We examined caudal anatomy in two species of prehensile-tailed lizards, Furcifer pardalis and Corucia zebrata. Although both species use their tails to grasp, each relies on a strikingly different anatomy to do so. The underlying anatomies appear to reflect phylogenetic constraints on the consequent functional mechanisms. Caudal autotomy is presumably the ancestral condition for lizards and is allowed by a complex system of interdigitating muscle segments. The immediate ancestor of chameleons was nonautotomous and did not possess this specialized anatomy; consequently, the derived arrangement in the chameleon tail is unique among lizards. The limb functions as an articulated linkage system with long tendinous bands originating from longitudinal muscles to directly manipulate vertebrae. Corucia is incapable of autotomy, but it is immediately derived from autotomous ancestors. As such, it has evolved a biomechanical system for prehension quite different from that of chameleons. The caudal anatomy in Corucia is very similar to that of lizards with autotomous tails, yet distinct differences in the ancestral pattern and its relationship to the subdermal tunic are derived. Instead of the functional unit being individual autotomy segments, the interdigitating prongs of muscle have become fused with an emphasis on longitudinal stacks of muscular cones. The muscles originate from the vertebral column and a subdermal collagenous tunic and insert within the adjacent cone. However, there is remarkably little direct connection with the bones. The muscles have origins more associated with the tunic and muscular septa. Like the axial musculature of some fish, the tail of Corucia utilizes a design in which these collagenous elements serve as an integral skeletal component. This arrangement provides Corucia with an elegantly designed system capable of a remarkable variety of bending movements not evident in chameleon tails. J. Morphol. 239:143-155, 1999. © 1999 Wiley-Liss, Inc.