Some plesiosaurs went for clams

Material found within the fossils of plesiosaurs unearthed recently in Australia suggests that some of the long-necked, aquatic reptiles had a different eating style than scientists had suspected.

The stomach contents of plesiosaurs previously excavated in North America and Europe included hard parts of belemnites—ancient sea creatures related to today’s squids—as well as fish. Paleontologists had speculated that such agile prey made up plesiosaurs’ main diet and that the dinosaurs used their long necks to reach victims without moving too near them, says Colin R. McHenry of the University of Newcastle in New South Wales, Australia.

Now, the last meals of two plesiosaurs dug up by McHenry and his colleagues in Australia and described in the Oct. 7 Science indicate that some of the creatures also used their necks to reach slow, bottom-dwelling prey.

Both plesiosaurs lived nearly 110 million years ago in a broad, shallow sea near what is now Australia, says McHenry. One plesiosaur’s stomach cavity included belemnite remains, but 92 percent of the contents were crushed shells of thumb-size clams and snails. The stomach cavity of the other specimen contained a crab shell, several fragments of other crustaceans, and a single fish scale. The digestive tracts of both plesiosaurs also contained dozens of gastroliths, stones that paleontologists speculate were used to grind up hard-shelled prey and thereby aid digestion.

The recently excavated plesiosaurs would have been 5 to 6 meters long and weighed about 1 metric ton when they were alive. Even so, the creatures may have been juveniles of the species, says McHenry.