Ammonites are among the most abundant yet beautifully preserved fossils on Earth. Many have tightly coiled spiral shells, although this Scaphites nodosus from the Cretaceous period is partly uncoiled. Although related to the modern-day nautilus, these cephalopods were actually more akin to the octopus, squid and cuttlefish. They died out at roughly the same time as the dinosaurs, after surviving for 300 million years before that. The biology of these extinct animals is the subject of Ammonites by Neale Monks and Philip Palmer (Smithsonian Institution Press/The Natural History Museum, $50 (hbk), $24.95/£15.95 (pbk)).