A truncated axial skeleton: The evolutionary loss (and reappearance) of vertebrae in anurans.

A defining feature of modern anurans (frogs and toads) is their truncated vertebral column. In most, the axial skeleton comprises no more than 9 pre-sacral vertebrae, a single sacral vertebra, and, post-sacrally, the urostyle. Tadpoles from one anuran family, Megophryidae, deviate from this pattern in bearing up to 30 supernumerary vertebral centra in their tails. The osteology and ontogeny of the expanded caudal skeleton of megophryids varies widely within the family, but for all genera, supernumerary vertebrae are resorbed at metamorphosis, presumably by osteoclastic degradation.