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Dinosaur Eater Is a Lot To Digest

Discovery Rewrites History of Mammals

By Joel Achenbach
Washington Post Staff Writer
Thursday, January 13, 2005; Page C01

Every single mammal learns from an early age that we used to get gobbled up by dinosaurs, that we were just a meaty little snack for the truly important animals of the Mesozoic, that we were small and meek and pathetic and cringing and whimpering and sniveling, locked into an extremely marginal evolutionary niche marked "Losers."

It's part of our mammalian heritage to pass this story on from generation to generation. Inevitably, our ancestors are described as mousy. "The size of a shrew" is a typical description. We came out only at night. Meanwhile the dinosaurs gallivanted all over the landscape, swinging their spiny tails around like they owned the place. We finally got our big break 65 million years ago when, luckily, a rock from space killed off the dinosaurs and much of life on Earth.

Repenomamus robustus and a finger pointing to its last meal, a baby dinosaur eaten 130 million years ago. (Frank Franklin Ii -- AP)

That story got amended yesterday, dramatically. Scientists at the American Museum of Natural History in New York announced that they'd found a 130-million-year-old mammal fossil that contains, in the remnants of the stomach contents, the tiny bones of a baby dinosaur.

Sometimes, we ate them.

"This is the first direct evidence that mammals fed on dinosaurs. Now we can say that dinosaurs could be very tasty, which is good news," said Jin Meng, a paleontologist at the museum and co-author of the paper, published in the journal Nature, announcing the discovery.

The dino-gulping mammal is Repenomamus robustus. It looked a bit like a very scary possum. Low to the ground, big teeth. Not the cuddliest thing you ever saw.

The baby dinosaur inside its belly is a psittacosaur, a humble plant-eater that when full grown was about six feet long. Actually there are just some fragmentary remains of the animal, including a couple of legs and some teeth. When you're someone's dinner you don't tend to look so good 130 million years later.

This dino-eating Repe (we can call it that for sake of ease, but don't try this in science class) was only about the size of a cat. But the scientists also announced the discovery of a remarkably complete fossilized skeleton of a much larger, related mammal, Repenomamus giganticus, which grew at least as large as a medium-size dog, more than three feet from nose to tip of tail. That's not shrewish.

Meng said the smaller Repe fossil, with the stomach contents, was dug up by a farmer two years ago in northeastern China, a country that has in recent years given the world some stunning fossils, including ones of dinosaurs with feathers. At first Meng believed that this fossil showed a mother and her baby, carried inside the womb. That by itself would make it a fascinating specimen.

But his colleagues, including one of his students, Yaoming Hu, the lead author on the Nature paper, discovered something tantalizing during a microscopic examination of the teeth of the smaller animal: They were dinosaur teeth. This was a belly full of baby dinosaur.

Some call it cold-blooded murder; others call it payback time.

The discovery is "a huge story," said Hans Sues, a Smithsonian paleontologist. "We really didn't think there were big mammals like that around in the Mesozoic . . . We're not dealing with some meek little insectivore. This is a major player in the ecosystem."

Meng said that mammals should no longer be seen as supporting actors in a drama dominated by dinosaurs: "Some of these mammals could be very nasty, and go out and maybe chase some of the small dinosaurs."

There are still a lot of uncertainties. It's not clear whether the Repe was a predator or a scavenger. Meng thinks there's good reason to vote for predator. It's three times the size of the baby psittacosaur, he noted, which fits into the typical predator-to-prey size ratio. Also, true scavengers (such as hyenas) are relatively rare.

There is wear on the teeth of the psittacosaur, suggesting that it wasn't an embryo but rather a hatchling. Meng was also intrigued by the fact that some of the bones of the dinosaur remain intact. The Repe didn't chew, but gulped. That's rather primitive for a mammal, Meng said. "It's more like a crocodile behavior."

Perhaps the Repe hunted in packs. The museum provided an illustration of the scene 130 million years ago, showing a group of them hanging out together, one feeding on the little dino. In the background is the requisite smoking volcano. Perched on a tree branch is a mysterious winged creature that may be the ancestor of the flying monkeys of Oz, and it seems to be serving as the lookout for the Repes. The Mesozoic must have been a lovely time, what with all those animals working as a team, like in "Ocean's Twelve."

Finally we must ask the obligatory question: What did dinosaur taste like? The current thinking among scientists is that birds are the evolutionary descendants of dinosaurs, and that probably tells us all we need to know about dinosaur meat. Tastes like chicken.

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