"Heads Up", Input/Output, ME Departments, December 2006

input/output

by Harry Hutchinson, Executive Editor

Heads Up

As animals go, it seems a far stretch from goats to dinosaurs. You have mammals on the one hand and reptiles on the other—not to mention size, and the distinction that one group is extinct while the other is still butting heads among us.

But they also have traits in common. Goats are quadrupeds and so were most dinosaurs. Goats have horns and so did some dinosaurs. Among other traits they share, the skulls of live goats and fossilized dinosaurs have sinuses. And that brings us to a key question: Why?

We humans have sinuses, too, and may suspect their function is to trouble us when the weather turns damp, to keep us humble. A more scientific explanation, though, is that human skull sinuses reduce bone mass to compensate for the heavy bones that support our big brains and let us eat almost anything we choose.

Link to the dinosaur: An FEA model (below) of a goat's head was put to the test because of traits it shares with horned creatures long extinct.

One theory about the sinuses in the skulls of goats and dinosaurs is that they serve as shock absorbers, cushioning the brain from concussion when creatures fight with their horns.

That explains why a scientist who describes himself as "primarily a dinosaur paleobiologist" came to perform essentially an engineering study of goat skulls to see if the hypothesis would hold up. It also explains why his research was funded by a group called the Jurassic Foundation, which offers grants for studying dinosaurs. According to the foundation, by the way, most of the money it disburses as grants comes from Amblin Entertainment and Universal Studios, which produced the movie Jurassic Park.

The paleobiologist is Andrew Farke, a Ph.D. candidate in the department of anatomical sciences at Stony Brook University in Stony Brook, N.Y. He decided to test that hypothesis about sinuses by modeling the skull of a domesticated goat and using finite-element analysis to compute mechanical events inside it. The goat was a handy subject, because there was experimental data to work with. According to a 1995 paper in the Journal of Zoology, two researchers, Carolyn Renzulli Jaslow and Andy Biewener, had dropped lead weights onto the skulls of dead goats and measured the impact with strain gauges. They hadn't been able to put strain gauges into the sinuses, but their numbers were a starting point.

An earlier computer analysis, conducted at the New York College of Osteopathic Medicine in Old Westbury, modeled a skull to examine the chewing mechanics of monkeys.

Farke said that "laid out a protocol to developing the skull model." Farke used the same FEA software, from Algor Inc. in Pittsburgh, that was used in the primate study.

He started by using computerized tomography to scan the head of a freshly killed goat. He said he took more than 400 images, each one mapping a cross-section of the head. He converted the images to jpegs and chose about 100 from which to create three 3-D models, which he built in CAD software from Solidworks Corp. of Santa Monica, Calif. One model represented the skull much as Farke found it. One had sinuses with the bony septa, which reinforce the sinuses, removed. Another was a skull with solid bone and no sinuses.

Farke opened the models in the Algor software and defined material properties. Information on the mechanical properties of bone was available in medical and biomedical journals, he said.

Expecting the animal to hold its neck stiff during an attack with its horns, Farke set the base of the skull as a boundary condition. Running the software on a laptop computer in Windows XP, he measured the deflection of the craniums under the impact of a single static stress event.

His results have not been fully analyzed yet, but so far it appears that the presence of sinuses, at least those without septa for support, weaken the skull roof and allow increased strain in the skull. That doesn't support the shock-absorber theory. Farke is leaning toward a belief that sinuses in the bone lighten the skull, making up for the weight of the horns and easing strain on the neck.

Farke has completed the computation of the third model, the one with septa in place, and expects to report a comparison of results from all three models early next year.