Hybodus fraasi shark, artwork. This species of prehistoric shark existed during the late Jurassic period (165-15MB0MB million years ago). Adult sharks measured up to 2.5 metres long and weighed up to 30MB0 kilograms. The dorsal fin had a bony spine, probably as a means of defence. It had two types of teeth, one set was sharp, suitable for catching slippery prey such as fish and squid. Another set were flat and more suited for crushing the casings of shelled animals.