Meeting Abstract
The convergent evolution of body elongation and limb reduction is an extreme, yet widespread phenotype among vertebrates, especially among squamate reptiles. In addition to snakes and amphisbaenians, lizards have independently evolved snake like bodies at least 25 times. Snake like form in lizards evolves either through the addition of trunk vertebrae or via addition of caudal vertebrae. Snakes evolved from lizards via the addition of trunk vertebrae, having about 200-300 vertebrae, far exceeding those of snake-like lizards, which have up to 110 vertebrae. These differences in vertebral number may lead to functional and kinematic differences between these convergent body shapes. Furthermore, because these taxa rely solely on the vertebral column for locomotion, understanding the flexibility of the column is vital to understanding limbless locomotion. Here, we compared the vertebral kinematics and function between three taxa, a robustly limbed lizard, representing the ancestral state (Lepidothyrus fernandi), a long tailed surface-dwelling legless lizard (Pseudopus apodus), and a burrowing snake (Eryx colubrinus). We simultaneously took high-speed video from the dorsal aspect to measure the number of bends per body length and high-speed X-ray video to measure vertebral joint angles. We hypothesized that the legless lizard would exhibit vertebral joint angles and bends per body length intermediate to the robustly limbed lizard and burrowing snake, owing to an increased number of vertebrae relative to limbed lizards, but still having fewer vertebrae than snakes. Our findings suggest that legless lizards do indeed exhibit intermediate levels of bends per body length and vertebral joint angles, as snakes exhibited the greatest degree of flexibility and were capable of much sharper bends.
