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MARGINALIA

The Cutting Edge

Can stone-tool marks on fossils be distinguished from tooth marks?

Pat Shipman

Cuts Versus Chews

I have great personal interest in this report on the Dikika fossils. Almost 30 years ago, Rick Potts, now of the Natural History Museum at the Smithsonian Institution, and I were the first to demonstrate (as we published in Nature) that the microscopic appearance of stone-tool cut marks is distinctly different from marks produced by animal teeth.

We had collected large samples of bones with marks of known origin, then “visually inspected” (eyeballed) and documented the marks under a scanning electron microscope. Our known samples included carnivore tooth marks, rodent gnawing, weathering, sedimentary abrasion, digestion, trampling, excavators’ marks, and root marks; the known samples expanded in number and diversity as years passed. By comparing the known pieces with each other and with the unknown ones, we were able to identify diagnostic characteristics that consistently showed up in true cut marks that were lacking in other kinds of marks.

Our paper on identifying surface marks on fossils kicked off a flurry of controversy and excitement. Some colleagues challenged our ability to make these identifications correctly. Others undertook parallel studies examining many different kinds of marks and surface damage, including percussion (hitting a bone with a stone tool to break it open). What once seemed simple is now complex. We now know that several types of marks can closely mimic cut marks, including trampling by animals and the action of crocodile teeth on their prey. Great care must be taken to distinguish such marks from cut marks.

In light of these findings, it’s no wonder that the startling interpretation of these two Dikika bones caused a major controversy to erupt over the identification of these marks.




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