The bite side of life
Sitting in his office, surrounded by dinosaur fossils, crocodile skeletons and computer-generated resin bone structures, Colin McHenry talks about his work with the animated manner of a man you might guess spent a fair amount of his boyhood catching lizards.
The question begs to be asked and sure enough, the answer is a sheepish affirmative and a confession that, as a child, his favourite television program was David Attenborough’s Life On Earth.
That fascination no doubt inspired McHenry’s research on the biomechanics of carnivorous reptiles and mammals, which seeks to unravel the lives of ancient predators such as dinosaurs and sabre-toothed tigers.
It is a highly specialised field of interest and one which has seen McHenry and his research partners break new ground in their use of three-dimensional computer modelling to predict the mechanical behaviour of the skulls and jaws of various extinct species.
Called finite element analysis, the technique is being harnessed by McHenry and his colleagues – including Dr Philip Clausen at the University of Newcastle, and the University of NSW’s Dr Stephen Wroe – as part of the work of the University of Newcastle’s Computational Biomechanics Research Group.
Early this year, the prestigious New Scientist magazine reported on the group’s work in modelling different species. The article discussed McHenry’s work in applying the laws of physics to these models to determine their biomechanics and ascertain exactly what these extinct animals were and were not capable of doing.
The New Scientist story included McHenry's discovery that the legendary fearsome sabre-toothed tiger actually had an astonishingly weak bite and that its ferocity came mainly from the piercing effect of its sword-like upper canines.
"These are the sorts of answers biomechanics can give us," McHenry said. "Using biomechanics, we can examine how an animal’s bone structure responds to different loads, including bite force."
The realisation that finite element analysis could be used to learn more about the mechanical behaviour of animals – living and extinct – came about through McHenry’s research interest on the behaviour of the pliosaur Kronosaurus queenslandicus, a large predatory marine reptile that lived in Australian waters during the Age of Dinosaurs.
McHenry said capturing a true picture of the ancient lives of the fossil super predators was a tricky problem.
"We cannot watch them hunt and so whether something like a Tyrannosaurus rex actually preyed upon well-defended herbivores such as Triceratops is open to question," he said.
"Even if the fossil record does not often catch predators in the act of attacking their favourite prey, all animals are subject to the law of physics and if T. rex is going to feed on a five-tonne horned dinosaur, then it needs a skull strong enough for the job.
"Engineers regularly use three-dimensional computer models to predict, or crash-test, the mechanical behaviour of man-made designs for aircraft, cars, bridges and buildings. The Computational Biomechanics Research Group uses the same tools to predict the mechanical behaviour of the skulls and jaws of dinosaurs and sabre-toothed tigers in order to infer predatory behaviour in these animals.
"Understanding the biomechanics of these fossil predators requires an understanding of biomechanics in living species, therefore much of our work is focused on the feeding mechanics of living species such as cats, dogs, crocodiles and sharks."
During his PhD research, McHenry built digital models of his ancient aquatic predators using finite element analysis and compared their behaviour to that of the modern crocodile, which led to his continuing analysis of skull biomechanics in crocodiles. Ongoing projects with other Computational Biomechanics Research Group members include experimental measurement of bone in mammals and reptiles, the first biomechanical analysis of a marine animal (the leopard seal) and technical validation data from primate models.
McHenry said the primary motivation for his research was to ascertain how an animal’s structure relates to its function.
"Biological structures are much more complex than traditional man-made objects in both their shapes and their composition of materials," he said.
"One of the spin-offs of developing tools which can model the biomechanics involved is an insight into the way organisms are engineered.
"This has significant potential application to medical biomechanics, including surgical repair of bone fractures and the development of orthopaedic prostheses like hip replacements.
"It can also be used to improve and develop the design of safety equipment."
McHenry said research was currently being undertaken on these new aspects of the work and points out how engineers, in turn, will also benefit "from understanding how nature uses composite materials, such as bone, to optimise strength and weight".