In mammals, cartilage is mainly an embryonic tissue, forming a model of the future bony skeleton. Cartilage persists permanently in relatively few places within the adult mammalian skeleton (e.g., in joints, as articular cartilage), and this permanent cartilage has a very poor capacity for spontaneous repair following injury. Cartilaginous fishes (sharks, skates and rays), on the other hand, possess a skeleton that is composed entirely of cartilage, and that remains cartilaginous throughout life. We recently discovered that skates have the capacity to grow new cartilage throughout adulthood, and to spontaneously repair cartilage injury. We aim to discover the cellular and molecular basis of adult cartilage growth and repair in the skate, and to use these findings to enhance cartilage engineering from mammalian progenitors.