An ancient porpoise that scientists believe lived off the California coastline 5 million years ago had an extremely long underbite, likely to help it forage for food.
Called the Semirostrum ceruttii, the porpoise has the biggest underbite ever seen on a mammal, the Los Angeles Times reported.
Scientists have found 15 fossil specimens of the porpoise, which they date from 1.5 million to 5.3 million years ago. They believe the animal thrived during the warm Pliocene era and may have become extinct because of climate change.
A bottom-feeding mammal, the porpoise probably lived in the shallow continental shelf, which spanned a large area during the high sea levels of the Pliocene era.
Recently published in the journal Current Biology, the findings show that the long underbite is an extension of the porpoise's jawline and had "extensive nerve canals" to send signals to the brain.
According to Rachel Racicot, a doctoral candidate at Yale University and the lead author of a paper, the extended jawline may have had the sensitivity of the human hand, something that would help the porpoise feel out the ocean floor.
Because the Semirostrum ceruttii had weak eyesight, the long underbite probably helped the animal seek out prey. It probably ate anything it came across, including crustaceans and squids.
"The extinct porpoise is a bizarre new animal, with the mandible extending well beyond the beak-like snout, which it may have used for probing and 'skimming' in the substrate," Racicot said in a press release. "Although this morphology has been recorded in birds and fish, this is the first described mammal with this anatomy."
While the extended jawline was too thin to help the porpoise scoop food into its mouth, Racicot believes the animal threw its back to catch the food in its upper jaw.
Researchers aren't sure why the porpoise became extinct, but they have hypothesized that its distinct underbite became a liability during the glacier Pleistocene era, when falling sea levels meant less continental shelf area.
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