New York: Even before the age of dinosaurs, massive relatives of the modern-day sharks ruled the waters of present-day Texas, reveals an analysis of fossils recovered recently from the region.
The researchers estimated that the fossils belonged to a time called the Carboniferous, dating back some 300 million years.
Previously, giant sharks had only been recovered from rock dating back 130 million years, during the age of the dinosaurs. The largest shark that ever lived, commonly called "Megalodon", is much younger, with an oldest occurrence only about 15 million years ago.
This means the two new fossils from Texas indicate giant sharks go much further back into the fossil record.
John Maisey of the American Museum of Natural History in New York and his colleagues estimated how big the entire sharks would have been by comparison with smaller and more complete fossils of closely related sharks.
The size range estimated for these two Texas 'supersharks' was between 18 and 26 feet in length.
The largest of these specimens was 25 percent bigger than today's largest predatory shark, the Great White.
These fossils may belong to an extinct species of shark called Glikmanius occidentalis, or they may represent a new and larger related species that is new to science, the researchers said.
The findings were presented at the annual meeting for the Society of Vertebrate Paleontology in Dallas, Texas.