Sharks swam in seas and rivers during the Carboniferous. Although they had evolved millions of years earlier, more distinct types lived in the Carboniferous than at any other time in Earth history.

Why So Successful?
Scientists think that two things helped sharks explode in diversity: few competitors for food and the absence of predators. Placoderms, which ate sharks and competed against them, went extinct around 345 million years ago—making life much easier for sharks.

Sharks Today
Modern shark lineages didn’t arise until the Cretaceous (145 to 100 million years ago). Although sharks are sometimes called "“living fossils,"” the sharks we know today have evolved a lot since their ancestors swam Carboniferous seas.

Shark skeletons are made of cartilage—the material that stiffens our noses—rather than bone.


  • Title: Modern-type crow shark
  • Location: Niobrara Formation, Logan Co., Kansas
  • Physical Dimensions: L: 210 W: 65 D: 5
  • Type: Fossil
  • Rights: This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws. http://www.si.edu/termsofuse
  • External Link: View this object record in the Smithsonian Institution Collections Search Center
  • Weight: 45 kg
  • USNM Catalog Number(s): PAL425665
  • Scientific Name: <i>Squalicorax sp.</i>
  • Photo Credit: James Di Loreto, Smithsonian Institution National Museum of Natural History
  • Historic Period: Lived 90–84 million years ago
  • Geologic Age: Mesozoic - Cretaceous - Upper/Late
  • Field: Paleobiology
  • Date Collected: 1987-07

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