It's smaller than a mouse, but this little character left behind the oldest primate fossils ever discovered in North America and Europe.

Its discovery in Mississippi represents a career triumph for Chris Beard, a paleontologist at the Carnegie Museum of Natural History in Oakland.

The arboreal "Teilhardina magnoliana" apparently was living in Mississippi in what was then the Gulf Coast 55.8 million years ago when a major episode of global warming was under way.

Later versions of the same primate turned up in interior North America and in Europe, but the ones Dr. Beard rediscovered first at Yale University then unearthed through digs in Mississippi have proven to be older.

His discoveries provide fresh insights about how the earliest primates migrated from Asia to North America then to Europe. His study will appear today in the Proceedings of the National Academy of Sciences.

The tiny primate first migrated to North America over the Bering land bridge that once connected Siberia with Alaska.

At one time different types of Teilhardina inhabited Asia, North America and Europe, making it difficult to reconstruct how they dispersed globally at a time when the climate was undergoing rapid change.

Dr. Beard said his research focused on studying erosional features created by changing sea levels, producing the 1-inch layer of sandstone in which the fossils were found. Comparison of the same erosional feature caused by falling sea levels in Mississippi versus Europe shows that the tiny primates in North America are older.

Dr. Beard said it reveals that the Teilhardina eventually crossed a narrow land bridge from North America to Greenland then Scotland, rather than vice versa.

At that time there was no ice at the poles. Changing volumes of ocean basins caused by continental drift caused the sea level to drop, exposing the land bridge.

Dr. Beard's entire study began with a lucky accident.

As a doctoral student at Johns Hopkins University, Dr. Beard said he was doing his thesis research at the Peabody Museum of Natural History at Yale University in the late 1980s and opened a museum drawer. Inside he found fossil teeth that immediately caught his attention.

He got permission to borrow the fossils then tracked down the amateur fossil collector who'd unearthed them. That collector led him to a site near Meridian, Miss., where he'd found the fossils.

Working at Carnegie Museum since 1990, Dr. Beard has made two trips a year to Mississippi to search for fossils and do research, which involved serious digging. That thin sandstone layer, at places, sits 8 to 10 feet underground.

"That's why it took so long to collect the fossils, study them and compare them with fossils from other sites," Dr. Beard said. "It's been a long time coming, but this is the culmination of almost 20 years since I first found out about the fossils."

Teilhardinas lived in trees in subtropical forests to avoid becoming a tasty morsel for larger mammals. The fossils, mostly teeth, are strong indicators of the species and its diet, Dr. Beard said.

Weighing about 28 grams, or roughly an ounce, the small primate was an acrobatic leaper and proficient climber. It probably ate insects, fruits, sap and gum.

The fieldwork involved a long-term collaboration between the Carnegie Museum and the Mississippi Office of Geology in Jackson, Miss., with funding provided by the National Geographic Society and the National Science Foundation.

The study stands as "the big triumph" of his career, Dr. Beard said, by providing insights into how early primates traveled the globe. It also reveals the complexity of ecological changes in North America, which eventually allowed the subtropical primates to migrate from the Gulf Coast inland to Wyoming and elsewhere as temperatures warmed.

Teilhardinas in Asia likely evolved into the gremlin-like animals nowadays known as tarsiers.

Dr. Beard said his next goal is to study the fossils of other mammals his crew unearthed in Mississippi to better understand the ancient ecosystem that included the tiny primates. He said his team has discovered a second thin layer of sandstone that might provide further evidence.

"I'm excited about it, and it makes us want to go back to Mississippi," he said. "When we started to find answers, it only raised more questions."