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Extinct porpoise had 33-inch long lower jaw for a purpose

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Move over Jay Leno. Scientists have discovered the fossilized remains of a porpoise with a very long chin.

The new species of porpoise, referred to as Semirostrum cerutti, has the longest chin length ever found in a mammal. Researchers believe that the extinct porpoise used its long lower jaw to look for food in the ocean floor. The scientists who discovered the porpoise published their findings in the online journal Current Biology last March 13.

"This is unique anatomy for a mammal," said Yale University doctoral candidate Rachel Racicot. "And it tells us that porpoises once searched for food in a very different way than they do now." Racicoot is also the lead author of the study.

Semirostrum is a species that is related to crown porpoises. Unlike its living relatives however, the new species of porpoise has a distinct extension of the lower jaw referred to as a symphysis. After measuring the fossilized remains of the animal, the researchers found that Semirostrum's symphysis was around 85 centimeters in length. In comparison, the symphysis of a modern crown porpoise measures a mere one to two centimeters in length. This ancient marine mammal is also closely related to narwhals, beluga whales and dolphins.

Due to the length of its lower jaw, the porpoise was highly adapted to searching for food in the sea bed. This type of behavior is referred to as benthic feeding. The researchers who wrote the study were able to examine a total of around 15 fossils found in different locations across the state of California. Scientists estimate that Semirostrum swam in the oceans around 1.5 to 5.3 million years ago.

"The unique mandibular and dental characteristics, along with robust scapulae, sternum, and unfused cervical vertebrae, support the interpretation that this species employed a form of benthic skim feeding by using its mandible to probe for and obtain prey," said Racicot and her colleagues.

Scientists took detailed CT scans of the best preserved fossil to study the physiology of this unique animal. Upon further analysis, Racicot and her colleagues found that the ancient porpoise had an extensive network of nerves from the symphysis to the skull. This shows that Semirostrum's long chin was very sensitive. This ability would have been essential to find food along the ocean floor.

The best preserved specimen of the ancient purposes was moved to the San Diego Museum of Natural History for safekeeping after the study was completed.

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