This article explores the application of finite element analysis (FEA) in studying the evolution of animals, including dinosaurs. Scientists have applied the method to determine how dinosaurs originally looked and functioned, and how they and other animals changed and evolved through the years. FEA is a useful tool to reconstruct the mechanical behavior of the muscle and skeletal system in zoological and paleontological studies because it is non-invasive and reconstructs stress at multiple sites and depths throughout the skeleton. It can be used to study extinct animals by way of their fossilized remains and can deal with complex geometries and load conditions. FEA is now routinely used to interpret skeletal forms for function in both medical and biological applications. The scientists believe that FEA will hopefully allow to see the effect of eating hard foods, such as the belemnites with their bullet-shaped guards. FEA allows a far more intricate, accurate, and precise picture of the bone to be used in studies.
Finite element analysis dates to around the 1950s, when its developers sought a way to carry out complex elasticity, airframe, and structural analyses. Recently, a group of scientists without an engineering background have turned to the method to help analyze structure and stress within extinct animals, and to get a look at how animals evolved.
FEA's use in studying the evolution of animals, including dinosaurs, dates to around five years ago. Or at least that's when the push to enumerate past FEA efforts in the fields of paleontology and zoology began, with the goal of furthering its use in animal studies.
Through use of a mesh—which looks rather like a net—placed over a digital model of the object to be studied, the analysis technique calculates the deformation in a structure when forces act on it. The points of mathematical analysis are the nodes—the points where corners of the mesh triangles meet.
Since its inception, the analysis method has been contained within a large number of software packages and has gone from helping specially trained engineering analysts study structural and elasticity problems to everyday use across a number of mechanical related fields.
Through the years, engineers in the biomechanical field have adopted the method. Engineers at Geass in Udine, Italy, for example, use the Femap FEA system from Siemens PLM Software of Plano, Texas, to design dental implants.
So perhaps it wasn’t too outlandish when a handful of paleontologists and zoologists came up with a way to use the method to analyze, retroactively, complex systems that were once alive. And no bones about it, dinosaurs were certainly complex in their structure and in their behavior.
With a strong push in 2007 from an Earth science professor at the University of Bristol in England, scientists have applied the method to determine how dinosaurs originally looked and functioned, and how they and other animals changed and evolved through the years.
FEA is now routinely used to interpret skeletal forms for function in both medical and biological applications, according to Michael Fagan, a professor of medical and biological engineering at the University of Hull in England. Fagan has coauthored a number of articles on the use of modeling and simulation in his field. Recently an article he coauthored in the January 2012 edition of the journal Biomechanics and Modeling in Mechanobiology looked at a way to account for muscles that have been wrapped with bandages when using a certain type of FEA to model a person's frame.
But the biomechanical field expanded even further. In 2007 the Earth science professor from the University of Bristol, Emily Rayfield, published a paper that charted FEA's use within the study of vertebrate evolution and its adoption by zoologists and paleontologists. That study appeared in the May 2007 issue of the Annual Review of Earth and Planetary Science and it pulled together much of the research done using FEA in the fields of paleontology and zoology.
The analysis method's use in those fields was in its infancy in 2007, Rayfield wrote in that paper.
“FEA is now widely used to assess the biomechanics of the human musculoskeletal system, including soft-tissue mechanics, heat transfer, and computational fluid dynamic problems such as blood flow,” Rayfield wrote. “Until very recently, however, its potential to engage in questions of vertebrate biomechanics and evolution remained largely unexplored.
“Crucially, a signature of loading history and hence function is recorded within bony tissue. Therefore, any technique, such as FEA, that enables us to reconstruct stress and strain within the skeleton allows us to explore questions of how that skeleton functioned and why evolution shaped it in a particular manner,” she wrote.
The process through which the load on a body influences skeletal geometry is known as mechanical adaption and many experiments have shown that an animal's bones evolve and change in response to the loads imposed on them, Ray-field wrote.
FEA is a good tool to reconstruct the mechanical behavior of the muscle and skeletal system in zoological and paleontological studies because it's noninvasive and reconstructs stress at multiple sites and depths throughout the skeleton. It can be used to study extinct animals by way of their fossilized remains and can deal with complex geometries and load conditions, she wrote.
Since that publication in 2007, Rayfield and her colleagues have gone on to regularly use FEA in their work, particularly in analyzing bone structures reconstructed from fossils.
“From these models we can get an idea of the type of behavior an extinct animal could perform, and why its skeleton was shaped in a particular way,” Rayfield writes on the website she maintains at seis.bris.ac.uk/∼glejr/.
Other students at the University of Bristol are also calling upon the method in their own work with fossilized remains, including Benjamin Moon, a Ph.D. student in the school of Earth sciences.
“As I’m sure many of you will have noticed, animals have a tendency to move about. This can be by walking, running, jumping, swimming, and flying,” he writes on the blog he maintains at ichthyosaurs.wordpress.com. “To do all of these, the animal must use its muscles and skeleton to apply forces through the feet, tail, and arms. When the animal works harder, more force is applied: doing a full press-up is more difficult than bending at the knees.”
Using muscles and bones to apply forces, doesn’t just make for movement, the bones themselves bend slightly too, Moon added. The greater the forces, the more the bone is deformed. If the force is too great, the bone breaks.
To study deformation, stress, and strain, Rayfield and her colleagues in the Palaeobiology and Biodiversity Research Group (palaeo.gly.bris.ac.uk) first take computer tomography scans of a fossilized skull, which they assemble into a three-dimensional digital dataset.
They overlay that 3-D model with an FEA mesh composed of a number of fixed points. The model is put through FEA software that applies forces to it. The software specifies the location and direction of the forces and finds any joins, sutures, and pivots on the skull.
The researchers can then calculate the stress and strain the skull once experienced, when it was part of an animal, Rayfield said.
The technique jibed exactly with Moon's modern-day sensibilities. Moon had been fascinated with dinosaurs since youth, but by the time he began working toward becoming a professional paleontologist, he was glad to see the field had moved on from simply naming animals.
The field is now more concerned with how extinct animals lived and interacted, Moon said.
“The chance to study this in ichthyosaurs was too much of an opportunity to pass,” Moon said.
How They Ate
He plans to use FEA to study the skulls of ichthyosaurs, recovered from the Oxford Clay Formation in south England. Ichthyosaurs were giant marine reptiles that looked like dolphins. They first appeared about 245 million years ago and disappeared about 90 million years ago, about 25 million years before all dinosaurs became extinct, Moon said.
During their stay, they evolved from still-unidentified land reptiles and moved back into the water, he added.
“The band of strata called the Oxford Clay Formation is made of very fine-grained sediments and it's thought that it once formed a soup-like mix of water and sediment above the sea floor, where there was little to no oxygen,” Moon said.
“When ichthyosaurs died they sank to the sea floor into the soup,” Moon added. “The lack of oxygen and soup-like substrate preserved the ichthyosaur nearly completely and in three dimensions. Most other ichthyosaurs are flattened by the weight of the rocks above, but the history of the Oxford Clay means this didn’t always happen.”
By using the University of Bristol's CT and FEA methods on skulls preserved in that once soupy mix, Moon hopes to discover the feeding mechanics of the ichthyosaur.
“Ichthyosaurs, especially from the late Jurassic, were shaped a lot like tuna and probably able to swim and sprint at quite a speed,” he said. “The effects of the skeleton and its biomechanics on streamlining and coping with the forces involved will be fascinating.”
In vertebrates, the most interesting applications of biomechanics center on the skull, as that's where eating takes place, Moon said. Also, the large number of bones in the skull makes for complicated, and sometimes unexpected, interactions.
“The skulls tell us a lot about how an animal lived; in particular, what and how it ate and how it could see,” he said. “Ichthyosaur feeding and some other behavior is usually thought to resemble that of modern dolphins, including their schooling behavior,” Moon said.
But he wants to see if that “usual thought” proves true.
“Using biomechanics, there have been many changes in perceptions of vertebrate feeding strategies,” he writes on his blog.
For instance, as a group of researchers wrote in a 2007 paper, pterosaurs—a group of flying reptiles that existed between 210 million and 65.5 million years ago—could not have skim fed, as had been thought, Moon said.
The paper, “Did Pterosaurs Feed by Skimming? Physical Modelling and Anatomical Evaluation of an Unusual Feeding Method,” appeared in the July 24, 2007, edition of the journal PLoS Biology (www.plosbiology.org/article/info:doi/10.1371/journal. pbio.0050204#cor1). The lead author for the paper was Stuart Humphries, then a fellow in the department of animal and plant sciences at the University of Sheffield in England, now a lecturer in marine biology at the University of Hull.
“Skim feeding requires dipping the lower jaw into water then closing the jaws when food is caught,” Moon wrote on his blog. “A pterosaur that tried to skim feed would probably break its bill!”
He's intrigued by the chance to study his chosen animal's skull.
“Ichthyosaur skulls are very odd for their time,” Moon said. “None of the bones are fused, as seen in mammals, birds, and some dinosaurs, and they possess a unique arrangement of bones at the back of the skull.”
He expects that arrangement of bones to prove crucial to ichthyosaur feeding, as it's located at the place where the jaw forms a joint with the cranium, he added.
Also, ichthyosaurs also have the unusual feature of a tooth groove rather than the sockets seen in many other vertebrate groups, including humans, Moon said. The groove holds teeth poorly: many fossils show that other dinosaurs lost their teeth completely, he added.
“FEA will hopefully allow us to see the effect of eating hard foods, such as the belemnites with their bullet-shaped guards,” Moon said. “FEA will show stresses and strains to skull.”
Belemnites are an extinct type of mollusk.
“Hopefully, this work will corroborate the fossils: belemnite guards have been found in the stomach region of ichthyosaurs so it is assumed that they ate them,” he added.
“Similar work with FEA is already being carried out at the University of Bristol on herbivorous dinosaur groups including sauropods—with their absurdly long necks—and therizinosaurs, which had claws over a foot long,” he said.
Unexpected results, he said, would add some spice to his project.
“If it is found that ichthyosaurs have an exceptionally strong biting force, it may be possible that they preyed upon the coiled ammonites,” he said. Ammonites are an extinct type of marine invertebrate animal closely resembling the modern Nautilus.
Furthermore, as ichthyosaurs were almost certainly aquatic animals, it may be possible to study the effects of moving through the viscous medium of water, Moon said.
CT scans and finite element analysis are giving scientists ever deeper insights into early forms of life and how they might have lived in their environments.
“FEA allows a far more intricate, accurate, and precise picture of the bone to be used in studies,” Moon said. “The ability to model the body in its true form means that we can successfully learn about the lifestyle of organisms, their ecology, and the ecosystems in which they were part.”