Pelvic girdle and fin of Tiktaalik roseae

Abstract

Significance: The earliest tetrapods have robust limbs, particularly hind limbs that are enlarged and supported by a number of modifications to the pelvic girdle. In contrast, the closest relatives of tetrapods maintain small and weakly ossified pelvic appendages as compared with the pectorals. This observation has led to the “front wheel drive” hypothesis that held that the closest relatives of tetrapods emphasized pectoral support and locomotion whereas significant pelvic support and locomotion was a tetrapod innovation. The discovery of pelvic girdle and fin material of the tetrapodomorph Tiktaalik roseae reveals a transitional stage in the origin of the pelvic girdle and appendage: although retaining primitive skeletal architecture, these elements are enhanced in size and robusticity much like tetrapods.