Forget what you know. Maybe.

The world of paleoanthropology — the study of the origins of mankind — is reeling this week from the shock announcement of a new discovery: fossil evidence of an extremely old cousin in a most unexpected location.

The place is the Rhine Valley of southwestern Germany. The discovery: two teeth from a human ancestor that are carbon dated at 9.7 million years old — more than twice the age of any human-like remains previously found on the planet.

The researchers are all stirred up, they said, because one of the teeth, an upper canine, is similar to the canines of humanity’s primitive ancestors, hominins. Up until now, teeth like this have been found only in Africa, not Europe. And the African specimens are much younger.

Since her discovery in 1974, paleontologists universally have claimed “Lucy” as our common ancestor. Lucy is the fossilized skeleton of the oldest known hominin. Although she stood only 3 feet 7 inches tall and looked more like a chimpanzee than human, Lucy’s leg bones resembled a modern human skeleton both in design and function. At slightly more than 3 million years old, Lucy was the first known primate that walked upright.

The discovery is “something completely new, something previously unknown to science,” says paleontologist Herbert Lutz, who directed the dig that found the teeth. Lutz said the discovery was made more than a year ago, but they were so baffled by the discovery that they held off publication of their findings until they were sure about what they’d found.

Assuming Lutz is correct, it means a very similar pre-human species was walking around northern Europe at least 5 million years before it inhabited eastern Africa.

That raises big questions that scientists had considered previously settled:

n Were the African and German species the same? If so, where did they originate? What was the pattern of migration?

n If they’re unrelated, how did the separate species originate? Did they develop similar characteristics by random chance, or were there environmental factors?

There are skeptics who dismiss the discovery as overblown and misinterpreted. They say the teeth likely belong to the broader primate group of hominoids, not hominins — which means they would be more distantly related to us than species like Lucy. They say a femur and hip bone would prove more than a tooth.

That’s a possibility Lutz and his team have been considering for more than a year. “We want to hold back on speculation,” he said.

“What these finds definitely show us is that the holes in our knowledge and in the fossil record are much bigger than previously thought.”

That’s a humbling thought. It seems sometimes that the more we know, the more aware we become of how much we still don’t know.