Sea Urchin Fossil
Sea Urchins (commonly called sand dollars) belong to a large group of marine animals called echinoderms. They are related to star fish and sand dollars. The spines, which do not usually preserve as fossils, serve not only as protection but can also move to walk the animal across the ocean floor.
There are about 7000 extinct species of sea urchins and about 900 living species. They first appeared in the Ordovician Period (434 to 490 million years ago) and subsequently became very diverse.
These fossils were found in Madagascar.