With technologies like CT scans and 3-D printing, a team of scientists reported on Monday that it had solved a mystery about the family tree of mammals that started with a single tooth a century and a half ago.

The tooth, found in Germany in 1847, was tiny and distinctive in shape — not quite reptile, not quite mammal. More fossils of that kind were found around Europe, but always just single teeth. Scientists named this group of animals haramiyids — Arabic for “trickster.”

The teeth were embedded in rocks as old as 210 million years, an era in which ancestors of the first mammals were evolving.

“These were some of the most enigmatic fossils for years,” said Neil H. Shubin, a professor of organismal biology and anatomy at the University of Chicago. “People didn’t know what they were at all.”