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Extinct Porpoise Discovered in San Diego Had a Major Underbite

It’s not every day that a new species of porpoise is introduced to the scientific world. However, that’s what recently happened when a team of paleontologists from Yale University, the San Diego Natural History Museum, the NYIT College of Osteopathic Medicine, and the University of Otago published a research article in the journal, Current Biology.

The article describes the fossil remains of a 3 million year old porpoise collected from Pliocene-age marine sandstones exposed in Chula Vista, National City, and San Diego. The scientists named the extinct porpoise, Semirostrum cerutti, in honor of Richard Cerutti, the San Diego Natural History Museum paleontologist that discovered the majority of the fossils.

The specimens, including a complete skull with the lower jaw, as well as additional lower jaws, vertebrae, ribs, and flipper bones, reveal an animal with a completely new and almost bizarre skull anatomy not represented in any living or fossil dolphin or porpoise.

The lower jaw, instead of ending at the tip of the rostrum, extended well beyond the rostrum to give the animal an extreme underbite. CT scans reveal an increased complexity in the internal ‘plumbing’ of the lower jaws that implies greater innervation and blood flow to this probe-like structure. This, in turn, suggests that the lower jaw may have served an enhanced sensory function in locating prey living on or within the sediment of the Pliocene bay that 3 million years ago occupied the area of what is now the greater San Diego-Tijuana metropolitan area.

The well preserved skull of Semirostrum cerutti is on permanent display at the Museum in the Pliocene portion of Fossil Mysteries.