Bob O’H brings an interesting Correspondence item in Nature to our attention. An excerpt is below:
Could Nature have been unknowingly publishing papers for the past 80 years about crocodilian gastroliths (stomach stones) instead of stones concluded to be 2.5-million-year-old hominid tools? This possibility could cast doubt, for example, on the nature of the Oldowan specimens described by Michael Haslam and colleagues in their Review of primate archaeology (Nature 460, 339-344; 2009).
Palaeontologists use a simple eyeball test to distinguish stone tools from gastroliths. If a specimen has wear marks on its outer surface but none on its inner surfaces, this indicates that the stone has been grinding away in some prehistoric stomach or other and is a gastrolith. But wear on both inner and outer surfaces indicates that it has been used for some sort of pounding or battering and can confidently be considered a tool. A quick look at the three Oldowan specimens reveals wear on only the extended surfaces, so they should be considered as gastroliths, not tools.
Identification of the Oldowan specimens as tools is based on the fact that the soft relict sands of Olduvai Gorge contain no natural stones of their own, so any stone found there must have been moved from distant river beds by some unknown animal transporter – concluded by high science to be Homo habilis. But crocodiles have the curious habit of swallowing rocks: these account for 1% of their body weight, so for a 1-tonne crocodile that’s 10 kg of stones in its stomach at all times. Surprisingly, science has never even considered the crocodile as transporter.
I haven’t read the chimpanzee archaeology papers (I don’t have access to them) but to claim Oldowan tools are gastroliths is simply nuts. The Olduvai Gorge material has been analyzed quite extensively and if one wanted to ignore the cores and bulbs of percussion, as well the lithic refitting, and the tracing back of the raw material to its source one could argue that Oldowan = crocodile gastroliths – not an argument I’d be willing to make.
Update 1: Dempsey gives the genesis of his idea here.