Would you eat a dinosaur? “No, I wouldn’t. I am actually a vegetarian,” said Duke paleontologist Anne Weil—but she admits that the recent fossil discovery showing that early mammals ate dinosaurs is certain to shake up the scientific community.
Last week, Chinese scientists announced the discovery of a pair of 130 million-year-old fossil remains that challenge long-held scientific beliefs about the relationship between dinosaurs and mammals. The two newly discovered fossils show that early mammals may have been carnivorous and higher in the pecking order than previously thought.
One of the fossilized remains—about the size of a small dog—is the largest and most extensive skeleton ever found of an early mammal. The smaller of the two mammalian remains has the stomach contents of a small dinosaur about five inches long, showing that mammals may have dined on more than just insects.
A team led by Jin Meng of the American Museum of Natural History in New York and Yuanqing Wang of the Institute of Vertebrate Paleontology and Paleoanthrophology in Beijing discovered the remains in the Yixian Formation, a rich fossil field in the Liaoning Province of China.
“We thought for a long time as dinosaurs as predators and mammals as prey. This may not be the case. Ecosystems were not as simple as that,” said Weil, who was not part of the research but wrote an accompanying article in the British journal Nature.
Weil also emphasized the lack of attention that the Chinese scientists—the original discoverers of the fossil remains—were receiving. “This is a shame, as the authors have far more interesting things to say,” Weil added in response to speaking on behalf of the scientists recently in the media.
Scientists believed that during the Mesozoic Era—the age of the dinosaurs from 280 million to 65 million years ago—mammals were no larger than modern rodents. In addition, Mesozoic mammals supposedly cowered in holes and underbrush in the presence of the towering dinosaurs, escaping at night to feed primarily on insects and small plants.
For decades, scientists assumed that mammals during the Mesozoic Era were small because it was the only size safe enough to survive in a world tyrannized by dinosaurs. Only when dinosaurs became extinct 65 million years ago was it safe for mammals to emerge and evolve to human beings, they thought.
The new discovery, also reported in Nature last week by Yaoming Hu, provides direct evidence that early mammals were carnivores, competing with dinosaurs for food and territory. The carnivorous mammals had limb joints typical of marsupials and other advanced mammals that allowed more flexibility of movement to compete for prey and evade predators.
“Now we’ve found relatively large mammals, and they were carnivores, which always are at the top of the food chain. This gives us a drastically new picture of many of the animals that lived in the age of dinosaurs,” Meng told the Chicago Tribune.
Although both species have no remaining descendants, the larger dog-sized mammal, which closely resembles a Tasmanian devil, has been named Repenomamus giganticus. The smaller mammal, Repenomamus robustus, swallowed a young psittacosaur—a horned dinosaur that was also known as a “parrot lizard” and could grow to be six feet long.
“One of the things that this find does is it shows that all early mammals were not small,” Weil said. “It unconstrains our thinking. It throws out why early mammals had to be small.”
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