Sharks: Monarchs of the Ancient Seas (PA-21)
Sharklike fish first appeared in the sea about 380 million years ago during the mid-Devonian time. These 2- to 4-foot-long creatures with broad, powerful tails were built for speed. Unlike their ancestors, they cruised actively instead of lying in wait for food. Primitive sharks, whose teeth are found in limestone of central Indiana, were common in the seas that covered the Midwest during Late Mississippian time. True sharks appeared about 170 million years ago and spread rapidly around the world. After marine reptiles became extinct about 70 million years ago, sharks became the dominant marine vertebrates. The giant was Cacharodon, ancestor of todays white shark, whose 6- to 8-inch-long teeth indicate that he was 45 to 50 feet long. Modern white sharks are 30 to 40 feet long and have 3-inch teeth.

Our Hoosier State Beneath Us: Paleontology