Cartilage comprises the skeleton of Greenland sharks.
Greenland shark . It has the longest known lifespan of all vertebrate species ( 392 ± 120 years ) , and is among the largest extant species of shark . Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton , five to seven gill slits on the sides of the head , and pectoral fins that are not fused to the head .