Lucy Dethroned — Oldest Humanoid “Little Foot”

The famous Lucy skeleton, our oldest documented ancestor, has been trumped by the more complete “Little Foot” skeleton as the prima donna of humanoid fossils.

In a paper released on Wednesday in the academic journal Nature, Little Foot’s discoverer Ron Clarke of the University of Witwatersrand in Johannesburg explained how he had been sitting on the discovery of the male humanoid for 20 years, searching not only to complete the skeleton, but for a new datinng technique that could accurately date Little Foot to Lucy’s time.

Previous attempts to date Little Foot, known with Lucy as part of the human ancestor-group Australopithecus, have provided a huge range of possibilities, from 2.2 to 4 million years old — 3.2 million being the age of Lucy. But a new technique called isochron burial dating put Little Foot at 3.67 million years old, beating out the old queen.

The dating technique looks at the sediment around a fossil to find the radioactive isotopes of aluminum and beryllium, which determine the last time the sediment was exposed to cosmic radiation; essentially, when it was last on the ground and not under it. Once underground and hidden from exposure to cosmic radiation, the isotopes remaining begin to decay at a steady rate, giving Clarke and his colleagues an accurate measuring stick. The best thing about the technique is that if the sediment was disturbed and brought back to the surface, scientists would see younger isotopes, so if there is one steady rate of decay, it can be assured that the sediment encasing the fossil (and hence the fossil itself) have not been disturbed since the isotopes began to decay.

As usual, not everyone is convinced. Nine out of the 11 sediment samples around the fossil date to 3.67 million years, however people like paleoanthropologist at the University of Stony Brook Fred Grine think the dating does not show that the age of the sediment and of Little Foot are connected. Grine told National Geographic that he buried a squirrel in his back yard last year, but the dirt he buried it in dates back to the ice age.

Still, Clarke and his team are confident that the new dating system works. Grine’s objection does not take into account the new isotope dating that would show when the sediment around his buried squirrel sunk deep enough from cosmic radiation to no longer develop isotopes, which would show when the squirrel was buried to a margin of error acceptable to geology. It is not about the sediment, exactly: it is about the isotopes.

Little Foot also has an intact skull while Lucy does not, so it has got that going for him.

Over 90 percent of Little Foot’s bones have been collected, while Lucy just has 40 percent. Looks like there is a new Australopithecus in town.