Western Interior Seaway
The Western Interior Seaway was a shallow sea filled with abundant marine life. This included predatory marine reptiles such as plesiosaurs, and mosasaurs that grew up to 18 meters long.  Other marine life included sharks such as Squalicorax and the giant shellfish-eating Ptychodus mortoni (believed to be 10 meters long). There were advanced bony fish such as the massive 5-meter long Xiphactinus – a fish larger than any modern bony fish. Other sea life included invertebrates such as molluscs, ammonites, squid-like belemnites, and plankton including coccolithophores that secreted the chalky platelets that give the Cretaceous its name, foraminiferans and radiolarians.