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Dinos for Dinner

By Joe McGowan

Last week, at the American Museum of Natural History in New York City, scientists announced a double discovery. While studying a fossil of a 130 million-year-old mammal called Repenomamus robustus (rih-peh-noh-mom-us roh-bus-tus), paleontologists from the U.S. and China found the fossilized remains of its last meal--a baby dinosaur. The mammal had devoured a psittacosaur (sih-tah-kuh-sore), a two-legged plant-eating dinosaur with a beaklike snout, also known as the parrot dinosaur.

The fossil was unearthed in Liaoning (leeow-ning) province in China. While examining the fossil, researchers noticed a set of bones under its rib cage, where the mammal's stomach had likely been. The bones were remnants of the limbs, fingers and teeth of a six-inch-long psittacosaur.

Some of the eaten dinosaur's bones were connected to one another, suggesting its devourer had swallowed or gulped large, unchewed chunks. The rare fossil is the first direct sign that early mammals may have fed on small vertebrates, including young dinosaurs. "This discovery is the chance of a lifetime," says Jin Meng, a paleontologist at the museum.

In a second exciting fossil find, a relative of robustus--Repenomamus giganticus--was unearthed. It is the largest known complete skeleton of a mammal from the Mesozoic era, 280 million to 65 million years ago. The animal was about the size of a midsize dog. That's much bigger than scientists thought Mesozoic mammals grew.

Competing with Dinosaurs
Together, the two discoveries give scientists a new understanding of ancient mammals and their ecosystems. †Previously, many paleontologists thought most Mesozoic mammals were no larger than squirrels and that they hunted mostly at night. †these smaller animals would have found it hard to compete with dinosaurs. †But the new finds suggest that some mammals were meat eaters that competed with small dinosaurs for food and land.

So did primitive mammals affect dinosaur evolution? It's still hard to say. "That's how it is with the best finds," says paleontologist Anne Weil of Duke University, in North Carolina. "They leave you with more questions than answers."

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