Styxosaurus was an elasmosaur, a long-necked variety of the marine reptiles called plesiosaurs. These sea monsters grew upwards of 40 feet (12 meters) long. About half that length was neck ...

Compared with ichthyosaurs and marine crocodile relatives, plesiosaurs fossils are rare. The discovery therefore offers a rare glimpse into the biodiversity of these long-necked marine reptiles.