Exactly why robber crabs have grown so big is a mystery, but with so few creatures making it to these remote islands, the giant crustaceans seem to have filled a niche normally taken by medium-sized mammals.
All 7 billion human beings on Earth weigh in at a hefty 287 million tons, but just one species of krill, which is that tiny crustacean eaten by large whales, weighs a total of 500 million tons on the scale together.
Walcott became a leading authority on trilobites and was the first person to establish that trilobites were arthropods, the group that includes modern insects and crustaceans.