Anyone who has been to the great pyramids of the Giza Plateau next to Cairo in Egypt may have noticed 1-3 Cm lens shaped fossils within the limestone, both underfoot and in the buildings themselves. These are nummulites, the shells of faraminifera. The biggest known are ten cemtimetres wide, and they are used as index fossils to age sedimentary rocks. They were particularly common in the Paleocene and Eocene, a period of high sea levels before glaciation lowered them, when what is now Egypt was under the remnants of the Tethys sea. They are still around today, and were named after the Latin for little coin.
via The Earth Story. Image credit: Fozy Istvan, via chronique du temps universel.fr.