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Friday, 23 February, 2001, 18:15 GMT
Dinosaur bites back
![]() Big Al: Like a blow from a hatchet
By BBC News Online's Ivan Noble
The dinosaur known as Big Al, or more formally Allosaurus fragilis, was a "slash and tear" feeder, not a bone cruncher like T. rex, a new study says.
They borrowed an engineering technique to analyse the forces at work in Big Al's skull and found it too light and unnecessarily strong to have belonged to a bone cruncher. A. fragilis probably tore at its food like a modern, giant lizard counterpart: the Komodo 'dragon' (Varanus komodoensis). Big Al - so called because the fossil skeleton found in the United States was almost complete - featured in the BBC programme The Ballad of Big Al, made by the Walking With Dinosaurs team. 'Weird features' The biggest of its kind were 12 metres (39 feet) long, stood three metres (10 feet) tall and lived during the late Jurassic period, around 150 to 145 million years ago. Emily Rayfield and her colleagues at Cambridge's Department of Earth Sciences wanted to try to explain the peculiar structure of its skull.
Dr Rayfield used a technique called FEA, or finite element analysis. "We built a digital model of the structure of the skull and then divided it into 3D blocks." She explained that once a computer knows the properties of each block - the elasticity for instance - it can calculate how the whole skull would behave under stress. Heavy hatchet The technique has been used for many years in engineering and orthopaedic design, but the idea of trying it on dinosaurs came when a colleague heard of a study on horses' hooves, she said. Modern cow bones are a near equivalent to dinosaur bones, so she used elasticity data from them, then calculated how strong the dinosaur's muscles would have been.
"There were two ways to explain this. Either it was overdesigned for day-to-day basic use or it was an adaptation to its feeding strategy: opening its jaws really wide and slamming its upper tooth row down into its prey," Dr Rayfield said. "Allosaurus generally used a high-velocity impact of the skull into its prey. An analogue would be a person wielding a large, heavy hatchet," she writes in the scientific journal Nature.
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