April 12, 2005

Biologist Compares Ant, Dinosaur Movements

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Saying, “You can learn about animal movement in an engineering sort of way,” Prof. R. McNeil Alexander, biology, University of Leeds explained many of the ideas behind animal motion in a lecture sponsored by Cornell’s Center for Applied Mathematics.

Alexander’s lecture covered a wide variety of topics related to animal mechanics, from whether or not dinosaurs were able to walk on walls and ceilings to how small animals do so today.

Alexander began his talk by discussing the Brachiosaurus, a dinosaur that weighed 50 tons — equivalent to ten billion ants or ten elephants. “How can an animal like that have the strength to stand up?” asked Alexander.

He explained that unlike modern reptiles, whose legs stand spread out, dinosaurs stood straight up similar to mammals. Dinosaurs were originally thought to have stood with their legs spread out, but according to Alexander, this would have made it impossible for large dinosaurs to carry their weight. By standing more upright, these dinosaurs reduced stresses on their bones.

“The faster you run, the greater the force you exert on the ground,” Alexander said, “When you sprint, the force to the ground is about 3 1/2 times your body weight. These pressures are enormous when dealing with animals of large size and brings into question whether or not animals as massive as dinosaurs could run.

Exploring the question of whether or not dinosaurs were able to run, Alexander examined footprints left by dinosaurs, all of which show the animals walking, not running. However, he said, “Just because there aren’t any footprints showing dinosaurs running doesn’t prove that they couldn’t run.”

To answer this question, Alexander measured the strength of a dinosaur’s bone relative to its weight and compared the ratio to those of modern animals. Animals with similar ratios have similar running abilities. According to Alexander, large dinosaurs such as the Apatosaurus could not run, while smaller dinosaurs such as the triceratops had considerable running ability.

The discussion also dealt with animal mechanics in a more general sense. According to Alexander, the larger an animal, the more efficiently it consumes energy. The cost of generating energy per unit of weight is greater for an animal like a mouse than it is for an animal like a horse. A galloping mouse takes four strides per gallop, while a horse only takes one.

“The tempo of life is always faster if you’re small,” Alexander said, pointing out that everything, from an animal’s heartbeat to its life expectancy, tends to be longer as the size of an animal increases. While larger animals consume energy more efficiently, smaller animals have an edge when it comes to scaling large inclines.

“A 60 degree hill is nothing to an ant,” Alexander said. Prof. John Guckenheimer, director of Cornell’s Integrative Graduate Education and Research Traineeship (IGERT) program, which sponsored the event, considered Alexander’s lecture a success.

“One of the areas that we are interested in is animal locomotion and robotics. I thought Alexander did a superb job in this talk,” said Guckenheimer.

Dan Riskin grad who is studying the locomotion of bats, agreed with Guckenheimer’s assessment of the lecture.

“The thing that is amazing is that [Alexander] knows more about the topic than anyone but he can explain it in an accessible way to a freshman. It shows how brilliant he is,” said Riskin.

Archived article by Daniel Palmadesso
Sun Staff Writer