Shedding light on Australia's dinosaurs of darkness
LAGs
New research by Professor Pat Vickers-Rich from the School of Geosciences at Monash University and Dr Tom Rich from Museum Victoria has changed the way scientists think about how dinosaurs lived.
Working as part of a group with colleagues from the University of Cape Town (South Africa) and the Museum of the Rockies (Montana, USA), the researchers made the breakthrough and at the same time disproved a long-held theory – their own.
During the Early Cretaceous Period (112-100 million years ago), Victoria was located within the Antarctic Circle. The climate of this region was, of course, extremely cold and the animals there – including dinosaurs – had to cope with months of darkness at a time. Scientists have been trying for decades to discover whether dinosaurs adapted in unique ways to survive in those conditions.
In 1998, Professor Vickers-Rich, Dr Rich and the group of researchers examined the bone microstructure of dinosaurs from Victoria. Due to the differences observed in the tissues, the team concluded that some dinosaurs survived harsh polar conditions by hibernating, while others evolved a physiology allowing them to be active throughout a full year. It was an hypothesis that received widespread attention.
New evidence, discovered while studying polar dinosaur bone specimens proves something quite different.
In a bone cross-section, lines of arrested growth (LAGs) resemble tree rings. And like tree rings, they are formed when growth temporarily ceases. Research on animals living today suggests that LAGs form annually, regardless of latitude or climate. Like tree rings, LAGs can be counted to age an animal, so that the absence of these marks likely indicates a dinosaur was less than a year old.
These marks have also been found in dinosaurs that lived at much lower latitudes, having no need to hibernate.
“The hibernation hypothesis was based on the presence or absence of lines of arrested growth,” said Professor Vickers-Rich.
“Our new analysis of polar dinosaur bones, shows that all but the smallest individuals possess LAGs.
“In addition to the presence of LAGs, the bone tissue organisation in the polar dinosaurs strongly resembled tissue seen in closely related dinosaurs from lower, more temperate latitudes. Based on bone microstructure alone, we can say that the dinosaurs living near the South Pole were not physiologically different from dinosaurs living anywhere else in the world during that time.”
Professor Vickers-Rich said these surprising results do not mean there was nothing unique about polar dinosaurs.
“It is very likely that dinosaurs living in different environments evolved specific adaptations – either physical or behavioral – to cope with environmental conditions. Analysis of bone microstructure can tell us a great deal about growth, but some things just aren’t recorded in bone tissue.”
Instead, the results hint at how dinosaurs achieved their 160 million year domination of the planet.
“If we were trying to find evidence of dinosaurs doing something much different physiologically, we would expect it to be found in dinosaurs from an extreme environment such as the South Pole. But based on bone tissues, dinosaurs living within the Antarctic Circle were physiologically similar to dinosaurs living everywhere else.
“This tells us something very interesting: that basically from the very start, early dinosaurs, or even the ancestors of dinosaurs, evolved a physiology that allowed an entire group of animals to successfully exploit a multitude of environmental conditions for millions of years,” said Professor Vickers-Rich.
The article was published in journal PLoS One: http://dx.plos.org/10.1371/journal.pone.0023339