There was a time, not so very long ago, when dinosaurs were portrayed as slow-moving behemoths, shuffling about with their tails dragging on the ground like a dead weight. But then a number of publications came out proposing that (at least some) dinosaur species were swiftly-moving animals with long flexible tails, held aloft. Then the popular film, Jurassic Park, was released, and the public saw iconic animals such as Triceratops and Tyrannosaurus rex -- and particularly my favourite, velociraptors -- as highly intelligent and swiftly-moving animals. But did Jurassic Park get it right? Did dinosaurs hold their tails up?
Yes, they did, according to professor Robert Full, a biomechanical engineer at the University of California, Berkeley. And the reason that dinosaurs held their tails aloft provides a glimpse into their natural history.
More than 40 years ago, paleontologist John Ostrom resurrected Thomas Huxley's idea that dinosaurs were more like flightless birds than lizards. Professor Ostrom added more credibility to the idea that at least some dinosaurs were agile, active predators when he published a book in 1969 proposing that theropod dinosaurs used their tails to stabilise rapid or abrupt movements (free PDF). Based on that information, perhaps some long-tailed lizard species have been misunderstood, too?
To answer this question, Professor Full and his team filmed how a lizard, the African red-headed agama, Agama agama, uses its long tail whilst running and vaulting from the top of a wall to reach the safety of a dark shelter placed high up on a shelf. The team then conducted the experiment again, but this time, the top surface of the wall was slippery, so the fleeing lizard lost its footing and ended up leaping at the wrong angle. But instead of crashing before reaching shelter, the lizard compensated by moving its tail up or down to adjust the attitude of its body, landing successfully.
But Professor Full and his team didn't stop there. They tested their findings by building a lizard-sized robot with an active tail that used sensory feedback to stabilize its pitch as it drove off a ramp. They found that a long, mobile tail was best for reducing midair body rotation when compared to a rigid tail, a passive (dangly) tail or no tail at all.
This elegant research shows that the evolution of a tail provides control over body rotation when moving abruptly or at speed. But more than providing support for a scientific hypothesis about the mechanics of animal movement and behaviour, these findings could have important implications for the design of manoeuvrable robots, too.
Here's Professor Full, telling us more about his latest research:
Libby, T., Moore, T., Chang-Siu, E., Li, D., Cohen, D., Jusufi, A., & Full, R. (2012). Tail-assisted pitch control in lizards, robots and dinosaurs. Nature, 481 (7380), 181-184 doi:10.1038/nature10710
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