Newly discovered fossils indicate that giant sharks swam ancient oceans much earlier than previously thought – by about 170 million years. Researchers from Dallas Paleontological Society recently discovered a pair of fossil braincases from a massive, now-extinct shark species dating to 300 million years. Previously, fossil evidence of "super sharks" dated to only 130 million years, to the age of the dinosaurs. These fossils represent ancestors of modern-day sharks and change the way scientists view shark evolution, according to the American Museum of Natural History.

For their study, researchers compared the fossil braincases to closely related sharks and estimated that these specimens belonged to an ancient shark species that would have measured between 18 and 26 feet in length – 25 percent bigger than the modern Great White. Comparatively, Megalodon – the largest shark species ever known – could have grown to be 67 feet in length, according to a news release. Megalodon, dates to 15 million years, making it much younger than the new fossil species. Modern-day sharks would represent a mere snack for a Megalodon.

Mark McKinzie and Robert Williams, excavators from the Dallas Paleontological Society, originally found the fossils hidden in rocks from Jacksboro, Texas. They've since been donated to the American Museum of Natural History in New York for further study.

The newly discovered fossil braincases may be members of an extinct shark species known as Glikmanius occidentalis, or they may represent an entirely new relative. Researchers recently presented these findings at the annual meeting for the Society of Vertebrate Paleontology.

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