Dog-sized dinosaurs that lived near the South Pole, sometimes in
the dark for months at a time, had bone tissue very similar to
dinosaurs that lived everywhere on the planet, according to a
doctoral candidate at Montana State University.
That surprising fact falsifies a 13-year-old study and may help
explain why dinosaurs were able to dominate the planet for 160
million years, said Holly Woodward, MSU graduate student in the
Department of Earth Sciences and co-author of a paper published
Aug. 3 in the journal "PLoS
ONE."
"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,"
Woodward said. "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," Woodward said.
Jack Horner, Woodward's adviser and Regents Professor of
Paleontology/Curator of Paleontology at MSU's Museum of the
Rockies, said Woodward's findings are consistent with other results
from the museum's histology lab.
"I think the most important finding is that polar dinosaurs don't
seem to be any different than any other dinosaurs in respect to how
their bones grew," Horner said. "Dinosaurs have annual growth lines
and those that don't have them are simply not yet a year old."
Woodward said she conducted her research after reading a 1998 study
about polar dinosaurs. Intrigued by the study, she decided to
review the findings and received a National Science Foundation
grant that allowed her to travel to Australia last summer, set up a
histology laboratory and analyze bones in a rare collection in
Australia's Melbourne Museum.
Woodward analyzed the bone tissue of 17 dinosaurs that lived 112 to
100 million years ago during the latter part of the Early
Cretaceous Period. All but one of the dinosaurs in her study were
plant eaters. All lived in the Antarctic Circle in what is now
known as the Australian state of Victoria.
Also participating in the study were the authors of the original
study: Anusuya Chinsamy at the University of Cape Town in South
Africa, Tom Rich at the Melbourne Museum and Patricia Vickers-Rich
at Monash University in Australia.
The three scientists who conducted the original study welcomed her
analysis and didn't mind that she falsified their hypothesis,
Woodward said. She added that the new study looked at more dinosaur
bones than the original study because more bones from the polar
dinosaurs were available. Paleontologists have been adding to the
collection over the past 25 to 30 years.
The original study looked at the bone microstructure of the polar
dinosaurs and concluded that the differences they saw indicated
that some dinosaurs survived harsh polar conditions by hibernating,
while others evolved in a way that allowed them to be active
year-round, Woodward said.
The new study showed that all but the youngest dinosaurs had "Lines
of Arrested Growth" or LAGs, Woodward said. Since the hibernation
hypothesis was based on the presence or absence of LAGs, the new
study falsified the hypothesis.
LAGSs, in a bone cross section, look like tree rings, Woodward
said. Like tree rings, they are formed when growth temporarily
stops.
"Research on animals living today suggests that LAGs form annually,
regardless of latitude or climate," Woodward said. "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 new study doesn't mean there was nothing unique about polar
dinosaurs, but those qualities aren't apparent in bone tissue,
Woodward said.
"It is very likely that dinosaurs living in different environments
evolved specific adaptations – either physical or behavioral – to
cope with environmental conditions," she said. "Analysis of bone
microstructure can tell us a great deal about growth, but some
things just aren't recorded in bone tissue."
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Article: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0023339
Thanks to Montana State University for this article.