This from a letter to Nature, in the latest edition:
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).
…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.
Read the full version here