"Popeye" Jurassic Mammal Found, Had "Peculiar Teeth"

Brian Handwerk
for National Geographic News

March 31, 2005

Paleontologists have unearthed a chipmunk-size creature from the late Jurassic period, and they say it could have a big impact on ideas about early mammal evolution.

The species is about 150 million years old and has the scientific name Fruitafossor windscheffeli. But noting the animal's enormous forearms, scientists nicknamed it "Popeye," after the cartoon sailor.

The small species is by far the earliest known burrowing mammal to have fed on communal insects, such as termites.

Until the new discovery, the most recent evidence of such behavior was only 50 million years old—a difference of about a 100 million years.

Scientists from the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, describe the fossil in tomorrow's issue of the research journal Science.

Popeye Forearms

Zhe-Xi Luo, led author of the paper, said he knew immediately that the find was unusual because of creature's distinctive teeth.

Unlike most known mammals of the period, Fruitafossor had teeth that each had a single root (a human molar has four roots), no enamel, and a wide opening at the root. So-called open-root teeth are common to animals that gnaw, such as beavers. Wide root openings allow teeth to quickly replace tooth material lost through intense chewing.

"These peculiar teeth in an otherwise very primitive Jurassic mammal were puzzling, as these teeth weren't supposed to appear until much later, when the armadillos evolved 50 million years ago, and again still later in form of the African aardvark," said Luo, who is the curator of vertebrate paleontology at the Carnegie Museum.

"Gradually we came to a startling realization that 150 million years ago, there was a separate evolutionary experiment by some Jurassic mammal in feeding on communal insects.

"Its teeth showed it probably lived like an armadillo," Luo added. "It most likely used its massive arms and claws to dig in the earth to eat colonies of termites and other invertebrates. But it was also capable of eating plants when insects weren't available. This type of adaptation occurred many times in mammalian evolution, but this is the earliest appearance."

Fruitafossor's Popeye-like forearms not only allowed the animal to burrow for insects but possibly to hide from Stegosaurus, Allosaurus, and other large dinosaurs of the day.

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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