Fossil Forebears : Tiny Teeth Show Wee Mammals Frolicked at Feet of Giant Dinosaurs

In a laboratory loaded with vertebrae the size of tricycles and leg bones as big as a man, George Engelmann peers into a microscope to study teeth so tiny that to the naked eye they resemble punctuation marks.

Magnified, the shiny black dots gain distinctive bumps and jagged edges marking them as teeth from minuscule mammals that scurried between the toes of dinosaurs 140 million years ago.

During the last five summers, Engelmann and volunteers have unearthed hundreds of teeth and tiny bone fragments of Mesozoic mammals, creatures the size of a shrew or a mouse, from a hillside at this national monument on the Colorado-Utah border.

These mammals shared the landscape with brontosaurs, stegosaurs, allosaurs and other dinosaurs, but their names--multituberculates, dryolesids and triconodonts--are not quite as familiar.

Most people are unaware that mammals were even around during the dinosaur days, said Engelmann, 38, a professor at the University of Nebraska-Omaha.

The popular view has dinosaurs ruling the Earth during the “Age of Reptiles” and mammals coming on the scene in the “Age of Mammals.” Mammals did not dominate until after dinosaurs died out, but many of those found by Engelmann’s research teams became extinct even before the dinosaurs.

“It’s just a general bias. It’s really tied to a very old notion, from Aristotle, that there were lower forms of life and now we are the highest. It’s nice to see that in the fossil record, to see obsolescent lower forms of life that eventually gave way to man,” he said.

“But that ain’t so. All mammals alive today must have had an ancestor in the Jurassic.”

Paleontologists may never be able to determine that one mammal ancestor, Engelmann said. “The odds of being able to do that are negligible. It tends to obscure what you can do--find close relatives and figure out relationships.”

This summer, the project hit the Jurassic jackpot with the discovery of an almost complete upper jaw and skull, with teeth intact, and part of the lower jaw of a multituberculate. The toothy jaw removes some guesswork from identifying the scores of other mammal teeth.

“It’s really a big help,” Engelmann said. “The more complete the fossil record, the more information we have for figuring out biological relationships. We can do it with isolated teeth, but it’s more difficult.”

Teeth have long been used to differentiate mammals because “almost every species has something peculiar in their teeth,” a cusp or bump or point that belongs to that mammal species alone, he said.

At least 50 species of Mesozoic mammals have been identified through teeth and bones found in Wyoming, Colorado and Portugal, but the fossil record remains sketchy.

“Probably all the Jurassic mammals found would fit in a few filing cabinets,” Engelmann said. Small things tend not to be preserved as well as large things, and not many people have looked for fossils from the Jurassic period, a 70-million-year-long period ending 140 million years ago.

More vertebrae paleontologists work with mammal fossils from a more recent time--70 million years ago. There are more fossils available, and the mammals more closely resemble present-day animals.

Finding mammal fossils at all requires patience, persistence and luck.

Engelmann began his search after a call from a graduate school friend, monument paleontologist Dan Chure. The first year, Engelmann, Chure and their wives found four mammal teeth at a site overlooking Rainbow Park campground.

“Four teeth sound great when you don’t have any,” said Engelmann. “If we had gone five years and not found any teeth. . . .”

But that did not happen.

He has found more than 100 in the last three years with the help of volunteers from Earthwatch, a nonprofit organization that provides money and people for research projects around the world. The volunteers, with a minimum of training, pay their own way and provide valuable help during two-week stints in the often-tedious, time-consuming job of gathering material.

Digging for miniature fossils means carefully prying away pieces of gray mud stone with ice picks, looking for evidence of bone in the rock. Promising flecks are circled with black marking pens, then the piece of rock is wrapped in toilet paper and carried back to the monument’s lab to await more chiseling.

The rock without dots also eventually makes it back to the lab, where it is soaked, washed and strained through screens to yield the even smaller grains of dirt and rock that get microscopic inspection.

About a fourth-cup of the sifted mix is poured into a jewelry-size white box and examined under the microscope. The volunteers use forceps to pluck the black bits of bone and the occasional tooth from the mostly gray dirt and rock.

Any fossil prizes are plopped into pill capsules or tiny vials.

The search for mammal fossils often turns up huge shoulder blades, ribs, dinosaur teeth, crocodile teeth or turtle shells. Although it’s not what Engelmann is looking for, “It’s always fun to find something, whether it’s a big dinosaur tooth or dinosaur bones. It could be something new.

“It’s less exciting to find more of the same. You know you will have to work at it to get some information out of it.”

Information buried in the fossils can help fine-tune the picture of what the world was like 140 million years ago, Engelmann said. “You can tell a lot about the physical condition from geology, the distribution of a species. To the extent you can figure out what the world was like, you have more information to answer questions about the modern world.”

There’s no guarantee the information will be useful, he said, but “the way I see it, science is an extension of a basic human activity. You find things out because you are curious. Some things you find out are useful.”