About 300 million years ago, during the Carboniferous period, mega sharks thrived in the Western Interior Seaway, a shallow sea that covered what is now Texas.

Fossils of these ancient creatures were unearthed in Jacksboro, Texas. The find, which included two fossilized braincases, gave scientists hints on the size of these beasts when they were still alive.

Measuring about 26 feet long, or nearly half the length of a school bus, these ancient marine predators were 25 percent larger than the present-day great white shark.

The researchers said that the braincases, which make up the back end of the skull of sharks, resemble the skull parts of other fossil sharks from the Paleozoic era albeit the former were distinctly different from the shorter back skull regions of present-day sharks.

The newfound shark though was not as large as the Megalodon, which lived about 16 million to 2.6 million years ago and grew up to 59 feet long.

Paleontologist John Maisey, from the American Museum of Natural History in New York City, who presented the findings at the 75th annual Society of Vertebrate Paleontology conference, in Dallas, Texas earlier this month, said that although scientists have discovered fossils from large ancient sharks before, none has been this old.

Until the discovery, the oldest giant shark was unearthed in 130 million year old rocks. The age of the newly discovered supersharks made them a valuable find since it indicated that giant sharks existed before the age of the dinosaur, which emerged around 230 million years ago. This means that these predatory beasts existed further in fossil record than previously believed.

Maisey and colleagues compared the fossils with smaller but more complete fossils of closely related sharks and estimated the size range of the Texas supersharks. The bigger of the two was found to be 25 percent larger than the biggest predatory shark that live today, the Great White, and more than three times longer than other fossil sharks, which include the Goodrichthys eskdalensis shark that was unearthed in Scotland, which measured between 6.5 feet and 8.2 feet from head to tail.

The Texas supersharks may be related to an extinct shark characterized by long body and forked tail called the Glikmanius occidentalis but scientists need to look at more specimens to be certain.