Old shell beads in Dorothy Garrod's stuff

It's a really short paper in Science by Marian Vanhaeren and colleagues:

Perforated marine gastropod shells at the western Asian site of Skhul and the North African site of Oued Djebbana indicate the early use of beads by modern humans in these regions. The remoteness of these sites from the seashore and a comparison of the shells to natural shell assemblages indicate deliberate selection and transport by humans for symbolic use. Elemental and chemical analyses of sediment matrix adhered to one Nassarius gibbosulus from Skhul indicate that the shell bead comes from a layer containing 10 human fossils and dating to 100,000 to 135,000 years ago, about 25,000 years earlier than previous evidence for personal decoration by modern humans in South Africa.

There's also a news story by Kathleen Wren:

At the Natural History Museum in London, the research team found a pair of shells among the other remains collected from the Israeli site of Skhul in the 1930s by British archaeologists Dorothy Garrod and Dorothy Bate. The shells are from the same genus, Nassarius, as those from Blombos.
The researchers tracked down another perforated Nassarius shell at the Musée de lHomme in Paris. It had been tucked away in the same small tin since it was discovered at the Algerian site of Oued Djebbana in the late 1940s.

I wonder why the same species of shells again and again. Is this just because Vanhaeren et al. were only looking for that size of shells, or because the hominids chose only that kind? Those aren't the only marine gastropods they might have picked, I assume.

Which is a bit of a worry, if the way you eat them is to knock them on a rock and take out the insides. That's what they do to these things on Survivor, anyway. That would account for the human agency getting them to the sites.

I would say they are lucky that the Algerian site is far from the sea (the paper says minimum 190 km); I would tend to think you wouldn't carry a seafood snack with you that far. On the other hand, that site is uncertainly dated and can only be pinned to > 35,000 according to the paper. And there is no certainty that the shell actually is that old from within the sequence, because they do not know the length of the deposit.

You know, the more I read this, the less convinced I am. And Science and Nature have had a lot of these "digging stuff out of drawers" papers lately. Hmmm....