New Research at Australia's Adelaide University suggests that contrary to some beliefs, dinosaurs were active and even fast-moving creatures, not cold-blooded and sluggish. Professor Roger Seymour from the University's School of Earth & Environmental Sciences has applied the latest theories of human and animal anatomy and physiology to provide an insight into the lives of dinosaurs.
Human and animal bones are not static structures but living and changing ones. They have tiny holes, called the "Nutrient Foramen" which allows blood to flow to the living bone. Simply put, the the larger the holes, the more active the creature is. Professor Seymour has used this principle to evaluate the activity levels of dinosaurs. The Adelaide University study looked at dinosaur bones and compared them to modern day mammals and reptiles.
"Far from being lifeless, bone cells have a relatively high metabolic rate and they therefore require a large blood supply to deliver oxygen. On the inside of the bone, the blood supply comes usually from a single artery and vein that pass through a hole on the shaft - the nutrient foramen," he says.
Professor Seymour wondered whether the size of the nutrient forearm might indicate how much blood was necessary to keep the bones in good repair. For example, highly active animals might cause more bone 'microfractures', requiring more frequent repairs by the bone cells and therefore a greater blood supply.
"My aim was to see whether we could use fossil bones of dinosaurs to indicate the level of bone metabolic rate and possibly extend it to the whole body's metabolic rate," he says. "One of the big controversies among paleobiologists is whether dinosaurs were cold-blooded and sluggish or warm-blooded and active. Could the size of the foramen be a possible gauge for dinosaur metabolic rate?"
Comparisons were made with the sizes of the holes in living mammals and reptiles, and their metabolic rates. Measuring mammals ranging from mice to elephants, and reptiles from lizards to crocodiles, one of Professor Seymour's Honours students, Sarah Smith, combed the collections of Australian museums, photographing and measuring hundreds of tiny holes in thigh bones.
© 2010 The University of Adelaide
"The results were unequivocal. The sizes of the holes were related closely to the maximum metabolic rates during peak movement in mammals and reptiles," Professor Seymour says. "The holes found in mammals were about 10 times larger than those in reptiles."
These holes were compared to those of fossil dinosaurs. Dr Don Henderson, Curator of Dinosaurs from the Royal Tyrrell Museum in Alberta, Canada, and Daniela Schwarz-Wings from the Museum fÃƒ ¼r Naturkunde and Humboldt University Berlin, Germany, measured the holes in 10 species of dinosaur from five different groups, including bipedal and quadrupedal carnivores and herbivores, weighing 50kg to 20,000kg.
"On a relative comparison to eliminate the differences in body size, all of the dinosaurs had holes in their thigh bones larger than those of mammals," Professor Seymour says.
"The dinosaurs appeared to be even more active than the mammals. We certainly didn't expect to see that. These results provide additional weight to theories that dinosaurs were warm-blooded and highly active creatures, rather than cold-blooded and sluggish."
These findings are were published in the prestigious Proceedings of the Royal Society in London, and will give scientists new tools to analyse the activity of animals, both existing and extinct.
Top Image: Original skull of Triceratops displayed in the Houston Museum of Natural Sciences in Texas, U.S. Photo by Nekarius/Wikimedia Commons.