type specimen

Twenty-three of the 52 specimens were "type specimens," the gold standard designating a species against which all other samples are measured.

The shoulder bone is especially valuable because it was the first A. sediba fossil to be discovered and is the reference, or type specimen, that defines the species.

"The whole point of a museum," said Means, is to take care of type specimens "in perpetuity."

For example, the 170-year-old type specimen has bright yellow glass eyes and legs that have faded to pale brown.

Likewise, museums hold type specimens of fossils, meteorites and biological samples.