Limbs to fins: the remarkable evolutionary story about limb reduction in gymnophthalmid lizards

KOHLSDORF, T.; GRIZANTE, M.; DIOGO, R.; ABDALA, V

Barcelona

Congreso; International Congress of Vertebrate Morphology; 2013

International Society of Vertebrate Morphologists

The tetrapod limb is composed by different tissues, such as muscles, bones, tendons. Most developmental and comparative studies seeking for associations between hard and soft limb tissues focus on pentadactyl models, but the implications of such studies must be tested by taking into account deviations of the pentadactyl norm, such as the extreme cases of digit reduction/loss observed in some vertebrate lineages. We investigate the relationships between muscles and bones in the tetrapod limb through a comparative analysis of limb myology among gymnophthalmid lizards, which exhibit a remarkable variation in limb morphology and different grades of digit and limb reduction. In gymnophthalmids, loss of only one forelimb digit implies 1) a slight reduction of the musculature, which is somewhat decoupled from bone reduction, and 2) new patterns of muscle attachments that seem to be related to both the topological position and morphological identity of the bones where the muscles attach. Transitions from a pentadactyl limb morphology to a spine-like appendage dramatically affect the configuration of bones and muscles. Within these extreme transitions, muscle reduction can be interpreted as an evolutionary reversion to a plesiomorphic configuration similar to that present in the fins of a last common ancestor of sarcopterygian fish.