Challenge

Studying species that have been extinct for 65 million years is naturally not without its problems. The few clues that have survived the aeons can only be uncovered by months, sometimes years of painstaking physical effort. Only then can the detective work really begin. Fortunately, technology itself has been evolving and is starting to make life a little easier.

Emily Rayfield is an Earth Sciences PhD student at Cambridge University. She is studying the structure of dinosaur skulls in an effort to determine how and why they evolved to reach the state they did. "There is an incredible diversity in the range of dinosaur skeletons and we are only now beginning to realise just how well evolved they were," she says. "My work reveals how the skull performs mechanically when experiencing every day loads associated with prey capture and feeding. I'm also looking at whether the skull is efficiently designed for feeding and ultimately just how strong it is."
 
Solution

Determining the biting strength of an animal that has been dead for millions of years requires the kind of combination of detective work and technology normally associated with forensic pathology. In this case, the technology comes in the form of COSMOS, the leading desktop-based FEA solution.

Emily makes extensive use of COSMOS in analysing the flow of forces within the Allosaurus skull under her best guess at typical loading. "I knew from previous projects about the principles behind FEA, but I had no practical experience of it in action," Emily says. "And with a background in zoology rather than engineering, it was important that I found a system that was easy to learn and use. I was convinced that COSMOS would fit the bill."

"I've found COSMOS pretty easy to pick up and the menu structure means that if I've forgotten how to do something I can usually work it out again pretty quickly," says Emily. "This is particularly important for me as I am not in a position to go through an extensive training program."

Details

The rarefied world of palaeontology seems an unlikely home for state of the art finite element analysis (FEA) software, but researchers at Cambridge University are never shy of merging disciplines to get the best results. So it is little surprise to find the Earth Sciences Department calling on the power of COSMOS, the powerful FEA suite from Structural Research & Analysis Corporation, in the quest for further understanding of our Jurassic forebears.

Man's fascination with dinosaurs is natural enough: the discovery that giant monsters walked the Earth such an unimaginably long time ago has probably fuelled the imagination more than any other scientific revelation. But the research that continues apace is about more than just a fascination with the extinct and the exotic. Examining the way that entire species lived and interacted with each other can yield important lessons about how life on earth works today.

The main focus for Emily's research is Allosaurus fragilis, a theropod from the Jurassic period whose fossilised remains have been found at numerous sites in the USA and Europe. The choice stemmed from the Allosaurus's unusual skull: an intricate arrangement of interlocking webs and cavities means the 80cm long skull is surprisingly light for such a large carnivore.

"It makes sense for a skull to be as light as possible: as well as being easier to carry, it also makes bone growth and renewal as cost-effective as possible," explains Emily. "This skull achieves lightness through such a complex design that it cannot have happened without a functional reason. I'm trying to find out how this apparently carefully evolved bone structure translated into biting strength to see if it can further our understanding of how Allosaurus hunted and fed."

Solution Reconstruction

Determining the biting strength of an animal that has been dead for millions of years requires the kind of combination of detective work and technology normally associated with forensic pathology. In this case, the technology comes in the form of COSMOS, the leading desktop-based FEA solution.

Emily makes extensive use of COSMOS in analysing the flow of forces within the Allosaurus skull under her best guess at typical loading. "I knew from previous projects about the principles behind FEA, but I had no practical experience of it in action," Emily says. "And with a background in zoology rather than engineering, it was important that I found a system that was easy to learn and use. I was convinced that COSMOS would fit the bill."

Emily's use of FEA is slightly unusual in that for her it is vital that as much geometric detail as possible is included in the analysis: an engineering analyst would almost certainly make simplifications to ease the computing burden by cutting out non-structural design details. Without no way of knowing for sure whether fine details are important or not there is no option but to include all of them. This, in turn, means that analysis times are necessarily longer, another reason for using COSMOS and its ultra fast solver.

Analysis constraints

Aside from this need for extreme detail, Emily's use of COSMOS and that of a more typical analyst, really only differ in the areas of geometry and boundary conditions. The former is a question of data capture, the latter, together with the small matter of material properties, of informed conjecture.

"The skull we have been analysing came from a site in the Rockies," says Emily. "For day to day measurements we use a full size plastic cast of the skull, but to capture the complete geometry accurately, the original fossil was subjected to a CT scan in a local Montana hospital. We used the resulting point cloud data as the basis for a CAD model of the Allosaurus skull which we can then analyse in COSMOS."

Setting the boundary conditions for the skull analysis means estimating the forces exerted by the dinosaur's jaw muscles. Unfortunately, few clues remain about the muscle tissue so Emily has to reconstruct the anatomy as best she can. "We can tell where muscles were attached and we can make intelligent guesses about the shape and size by looking at the anatomy of birds and crocodiles," she says. "We then physically build these presumed muscles in clay on the cast of the skull. This gives us accurate values for muscle cross sections that we need to make calculations of muscle strength based on anatomical studies of present day vertebrates. From these values of muscle strength we can then calculate biting forces at any point along the tooth row."

Armed with these derived forces and the precise geometry of the skull, all that is still required are the material properties of the bones themselves. Histological analysis of dinosaur bones suggests that they are similar in structure to fast growing mammals like cows. "As with the muscle structure, there is no way around this guesswork: the bones have been fossilised, irreversibly altering the mechanical properties in the process, so there would be no point in testing the original even if we were allowed to," says Emily.

Rapid processing

Having measured, calculated and estimated the principal variables in the FEA equation, analysis itself is, as it should be, a relatively painless experience. COSMOS meshes the 146 skull components with minimal intervention and performs the analysis of the 206,866 tetrahedral elements in a mere three-and-a-half hours running on a Sun UltraSpark.

"I've found COSMOS pretty easy to pick up and the menu structure means that if I've forgotten how to do something I can usually work it out again pretty quickly," says Emily. "This is particularly important for me as I am not in a position to go through an extensive training program."

Further analysis

Confident that the results she is already getting are going to further mankind's understanding of the evolution of dinosaurs, Emily is looking at ways she can hone her analyses still further. "Although I have modelled the individual bones of the skull separately, many of them have been fixed relative to each other for the purposes of the FEA," she explains. "In real life, some bones did move relative to each other. Permitting movement between these bones gives us a much more accurate picture of skull mechanical behaviour and performance. I will also be looking at modelling the individual muscles inside COSMOS to determine the stress flow even more precisely."

The story so far

Emily's work still has a way to go - she is aiming to complete her thesis by May or June next year and to have some of her findings published before then. Already, though, she is uncovering some interesting facts about her Allosaurus. "I've discovered that although the skull is incredibly lightly built, it's actually very strong," she says. "Differences in magnitude between biting forces and maximum loads the skull can withstand before yielding are leading me to some interesting conclusions about how this impressive animal may have captured and fed upon its prey."