Hi Ana
Good find and probably the answer to knotty's question...
1st answer: A pearl (or other object) was worn in a shell to hold it....
just turn the one on the right upside down, It is perfect for holding a tiny tresure, like a pearl.
2nd answer: they glued it to something, like a shell. I am pretty sure they had glue from sap, eggs, or horns and hooves.....
The flint instrument used to make holes was probably smaller and more pointy. The article indicates it was a flint tool similar to the one shown and chips often come off the larger tool that are quite sharp and pointy.
Just a guess but coincidently my BA is in Anthropology.....
Here is a similar article with more pictures and similar shell beads from Africa.
I just googled "oldest pearls" and my article on the pearl guide forum came up first. I think I will have to revise it. There have been several earlier discoveries published since I wrote that.....
OK now what kind of thread did they use? And what kind of knots?