Researchers studying Predator X asked Long to investigate why the creature used all four flippers for swimming. Madeleine was programmed to swim with two flippers, then all four. The robot demonstrated that using four flippers to swim could be a bad proposition, energy-wise. But they do provide a sort of turbo-boost for quick accelerations — handy for catching dinner.
"The otter and the pliosaur both swim the same speed," Long said, "but, man, that pliosaur can really take off."
The Preyro robot experiment allows Long to take his evolutionary studies a step further.
By setting up Preyro in a pool with another autonomous robot — a predator named Tadiator — Long and his students simulated an evolutionary scenario. They wanted to examine qualities that would help vertebrate sea creatures of the Cambrian Period forage for food without becoming lunch for predators. Specifically, they wanted to test the hypothesis that the ancient creatures' need to scoot away fast from predators drove the evolution of stiffer tails.
Students could stiffen Preyro's backbone by fitting plastic rings (representing vertebrae) over a jelly-like column running down the tail designed to simulate the biological structures of ancient sea creatures. More rings made for a stiffer tail.
They found that changing the size of Preyro's tail fin had no effect, but that backbones stiffened with vertebrae helped Preyro swim away from danger faster. Seven vertebra worked the best; any more made the tail too stiff. They concluded that the evolution of multiple vertebrae could have been influenced by the need to avoid predators while foraging.
Robot builders like Long still use computer simulations to complement their work. But Long says swimming robots like Madeleine and Preyro have advantages over computer simulations because it is extremely difficult to simulate the interaction between a flexible solid — like an animal's tail — and a liquid.
"The thing about robots is, robots can't violate the laws of physics," he said. "A computer program can."
Lauder said there's no substitute for building a device that can replicate the minutely complex features of an animal. He expects the rise of robots in biological research to accelerate as more advances are made.
"The next 20 years are going to be amazing, I think," Lauder said.