Scientists still don't know what the pocket is for, but they have guessed that it could be instrumental to the production or excretion of pheromones, according to the study.
The only other pocket shark ever seen by humans was an adult female, a little over 15 inches in length.
Mark Grace, the study's lead author, said in a statement that the new specimen was very young, young enough to have an unhealed umbilical scar. He was collected off the coast of Louisiana, which, Grace notes "has us thinking about where mom and dad may be, and how they got to the gulf," adding, "The only other known specimen was found very far away."
The new specimen was inadvertently collected in 2010 by the NOAA ship Pisces as part of a study examining the feeding habits of sperm whales. The shark was dead when first examined before freezing, about half hour after the catch, the study says.
Years later, Grace found the specimen among the frozen catch collected from the NOAA study.
Scientists don't know a ton about the pocket shark, which is one huge reason that the discovery of a second specimen is so exciting.
The pocket shark is a member of the shark family Dalatiidae, which means it could engage in a characteristic feeding method of the closely-related "cookie cutter" shark.
"Sharks of the genus Isistius (cookie cutter sharks) employ a unique feeding behavior that allows them to use their cookie-cutter-like teeth to excise a nearly symmetrical oval flesh plug from a variety of prey species including marine mammals, tunas, billfishes, and squids," the study explains.
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