Scattered across the vast Pacific Ocean that covers almost half the globe, is a multitude of islands. These are not fragments of any continent, but have grown completely independently of Gondwana. They have appeared mainly through volcanic action, where an underwater volcano has reached the surface and cooled. The flanks of these islands are further extended by reefs built up by corals and other sea creatures. Belonging to no recognized zoogeographic realm, this array of islands is described here as part of the Australasian ecozone.At the same time as the dinosaurs developed to be the most significant animals on Earth, other creatures evolved to dominate the seas. A group of animals of some importance were the ammonites, cephalopods that were encased in coiled shells, dating back to the Devonian. The shells consist of empty air chambers that can be used by the animal to regulate its buoyancy. The ammonites evolved into many shapes and sizes during the Mesozoic period and are commonly found as fossils in rocks that date from that time. The coconut grab is an unusual ammonite in that it can spend much of its time out of the water crawling about on land. On many of the tropical islands of the Pacific it can crawl up the beach and eat coconuts, and even climb trees to find the nuts when there are none available lying in the sand or washed up on the shore.