Name

Semirostrum (Greek for "half-beak"); pronounced SEH-me-ROSS-trum

Habitat

Coasts of western North America

Historical Epoch

Pliocene-early Pleistocene (5-1.5 million years ago)

Size and Weight

Undisclosed

Diet

Fish

Distinguishing Characteristics

Dolphin-like torso; protruding lower jaw

 

About Semirostrum

The prehistoric porpoise Semirostrum has been generating a lot of press, and for good reason: this ocean-dweller had one of the most distinctive jaws of any mammal, alive or dead, the lower part projecting a full seven inches past the upper part.

What's more, a detailed analysis has shown that this lower jaw, or "symphysis," was riddled with nerve openings, meaning that Semirostrum probably used its Jay Leno-like beak to roust up sediments from the ocean floor and feed on exposed fish and shellfish. (As distinctive a mammal as Semirostrum is, it didn't have anything on the marine reptiles that preceded it by a hundred million years; for example, the upper jaw of Excalibosaurus extended a full foot beyond its lower jaw!)