While the air breathing saurocetids have conquered most of the Photic zones of the ocean, sharks such as Xenohybodus maximus rule the dark abyss and frigid polar waters. These large chondrichthians migrate huge distances across the world's oceans, often followed by a convoy of parasites.  They often swim upstream, in fresh water to rid themselves of these vermin. Torpedo-like in shape, Xenohybodus will eat almost anything it can fit in its mouth (A recent stomach pump of a juvenile Xenohybodus show the remains of what looks to be a small theropod!).

    These sharks are solitary, only mysteriously gathering to mate in warm coastal waters.