in the Paleocene Oceans
marine world of the Paleocene was much more like the modern marine
realm than that of the Cretaceous. In particular, some of the largest
and most common Mesozoic animals had vanished. Although many Cretaceous
species of invertebrates and fishes
survived the Cretaceous extinction event, among aquatic reptiles only
turtles, crocodilians, and champsosaurs
(a freshwater, crocodile-like fish eater) persisted into the Paleocene.
Sharks are represented by mackerel sharks, several
genera of sand tiger sharks, and the first small-toothed white shark.
Bony fishes, especially
became more common as well. New forms of sea urchins and foraminiferans
appeared, alongside more modern forms of gastropods