Doing the walk of life

For 50 million years, animals have used the same food foraging techniques suggests research from the University of Southampton. The Lévy Walk consists of many small move steps, interspersed with rare long steps – theoretically the movement is optimal for locating sparse resources. It’s used by creatures including sharks, honeybees and penguins, but it was also used by sea urchins 50 million years ago. Analysis of fossilised sea urchin tracks preserved in rocky cliffs in Zumaia, northern Spain revealed that the animals used the same technique, suggesting it may have an even more ancient origin. “How best to search for food in complex landscapes is a common problem facing all mobile creatures,” said David Sims, Professor of Marine Ecology and lead author of the study published in PNAS. “Finding food in a timely fashion can be a matter of life and death for animals – choose the wrong direction to move in often enough and it could be curtains. But moving in a random search pattern called a Lévy walk is mathematically the best way to find isolated food.” Finding a signature of an optimal behaviour in the fossil record is exceedingly rare, Sims said, and will help scientists understand how ancient animals survived harsh conditions associated with the effects of dramatic climate change. “Perhaps it a case of when the going got tough, the tough really did get going,” he said. “The patterns are striking, because they indicate optimal Lévy walk searched likely have very ancient origin and may arise from simple behaviours observed in much older fossil trails from the Silurian period around 440 million years ago.” The collapse of primary producers – such as phytoplankton – and widespread food scarecity caused by mass extinctions, which appear in the fossil record, could have triggered the evolution of such searches. “It’s amazing to think that 50 million-year-old fossil burrows and trails have provided us with the first evidence of foraging strategies in animals that live on and in deep-sea floor – studies which would nearly be impossible and very expensive to do it modern oceans,” said Professor Richard Twitchett from the Natural History Museum. “Trace fossils are remarkable and beautiful records of the movements of ancient animals, which have been frozen in time and tell us so much about the evolution of life on Earth and the environment of the past.” Hierarchical random walks in trace fossils and the origin of optimal search behaviour