As the Turritella, the Sand Dollar is found in Tropical waters, and is another vestige in Peninsula Valdes from millions years ago that shows the possibility of a climatic cooling, and consequently a big water temperature change in the area.
If you find a fossil in the beach or in the cliffs enjoy it, think about how time pass by and about the world life but leave it in the area. By this way you are helping the ecological education and no the enviromental depredation, allowing other tourist and generations to have the chance to meet then. Take photos and leave your prints. Patagonia is a Paradise.