The megamouth shark is one of three species of shark – including the basking shark, pictured here – that eats plankton. The megamouth eluded discovery until 1976. Creative Commons

An extinct species of megamouth shark, an extremely rare type of deep-water shark, has finally been identified.

The prehistoric behemoth reached lengths of up to 27 feet and migrated between the deep and shallow waters of the Pacific searching for food. According to Live Science, the recently recognized massive megamouth shark roamed our oceans nearly 23 million years ago.

Scientists first found teeth from the ancient shark beginning in the early 1960s. NBC News reported that the teeth were recovered from the deep and shallow sediments off the coasts of California and Oregon. But because there was no known species of shark at the time to compare the teeth to, scientists weren’t sure what to do with the prehistoric choppers, and they ended up in a drawer at the Los Angeles County Museum.

Shimada recently came across the forgotten teeth, and when he discovered that no one was actively studying them, he and two other scientists took up the task.

The extinct species of megamouth, which, like today’s megamouth sharks, fed on plankton and small fish, had longer, pointier teeth than the modern megamouth shark has. Scientists also determined that the ancient creature had a slightly longer snout than its contemporary kin.

"That suggests that they probably had a wider food selection," study co-author Kenshu Shimada, a paleo-biologist at DePaul University in Chicago, told Live Science. "They could have probably eaten plankton, but they were also probably feeding on fish."

The modern megamouth shark has hardly ever been seen in the wild. Scientists didn’t even know the creatures, which live in deep waters and can grow to over 18 feet in length, existed until 1976 when one got caught in a U.S. Navy ship anchor near Hawaii. According to the Florida Museum of Natural History, there were only 53 confirmed sightings and one unconfirmed sighting of the megamouth shark as of 2012. It is one of three plankton-eating sharks and, like the whale shark and basking shark, swims with its mouth wide open, filtering the water for plankton and jellyfish.

"It was a species that was known to be a new species for a long time," Shimada said during the 73rd annual meeting of the Society for Vertebrate Paleontology. "But no one had taken a serious look at it" until this recent study.

The study will be published in an upcoming issue of the Journal of Vertebrate Paleontology.