Unlike most turtles, whose shells are made of expanded and fused bones that form a relatively solid dome, widely spaced bones that looked more like the rafters of a roof held up Protostega's ...

Look for the sagittal suture – the squiggly line that runs the length of the skull – and note whether is it's completely fused ... pitted and craggy these bones will be.

Sharks don’t have bones. Their skeletons are made of cartilage - the same ... their skeletal structure helps give some species of shark a powerful bite. Their upper jaw is not fused to their ...