The creature measured only about 6 inches (15centimeters) and weighed just an ounce (30 grams). Most other Late Jurassic mammals were also small insect-eaters.
Scant Fossil Remains
Such animals are difficult for paleontologists to study because of their small size: Significant fossil remains of small mammals are far more rare than those of large dinosaurs that lived at the same time.
In most cases, only teeth or jaws from small, ancient mammals are found.
"Getting something more than that—a partial or compete skeleton—is a real plus [that] usually reveals all kinds of surprises," said Hans-Dieter Sues, an associate director for research and collections at the Smithsonian Institution's National Museum of Natural History in Washington, D.C.
Fruitafossor's "teeth themselves are just odd," he noted. "But when you see them in the context of having these robust arms with all kinds of features for digging, the idea of [communal-insect eating] makes sense."
Scientists named Fruitafossor windscheffeli after longtime Carnegie museum volunteer Wally Windscheffel—who discovered the fossil in 1998—and Fruita, Colorado—the town close to where the specimen was found. As for fossor, it means "digger" in Latin.
The researchers anticipate tiny Fruitafossor will enjoy great stature in the study of early mammal evolution. Until recently most dinosaur-era mammals were believed to be simple, ground-dwelling insect eaters. Fruitafossor, however, appears poised to change that perception.
The chipmunk-size creature is getting help from other recent finds, including 130-million-year-old Repenomamus robustus. The cat-size mammal from China was described earlier this year. (Read about the discovery.)
R. robustus had the remains of a baby dinosaur in its stomach—the first proof that mammals weren't always below dinosaurs on the food chain. Meanwhile, Sues, the Smithsonian paleontologist, said that the key to Fruitafossor is that it "shows that very early in mammalian evolution, there was already a much greater diversity and a broader range of ecological adaptation than [previously] thought."
He added that Fruitafossor is "a real surprise. … But it is also consistent with discoveries in recent years that suggest mammals were already flourishing in the age of the dinosaurs. It had been thought that they didn't do much of interest until dinosaurs became extinct [about 65 million years ago.]"
Luo, the lead study author, said, "Like today's armadillos, [Fruitafossor] diversified in the past in an independent evolutionary event.
"This particular evolutionary experiment failed, because it did not save Fruitafossor's lineage from going extinct. But it still speaks to the fact that early mammals were far more diverse than we previously envisioned," Luo said.
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