Did You Know . . .

The waters of the WIS were warm, shallow, and inhabited by a plethora of marine animals. These included bony fish (including the monstrous Xiphactinus, or X-fish), sharks, marine reptiles such as mosasaurs and plesiosaurs, birds, mollusks (including ammonites, bivalves, and snails), and echinoderms (including echinoids and crinoids). Winged pterosaurs also flew overhead. Conditions on the WIS ocean floor were periodically anoxic (with little or no oxygen). Because of this, dead animals that sank to the bottom of the WIS often decomposed slowly, favoring their preservation as fossils.