Fossil bone tissue provides new insights into the lives of Australia’s polar dinosaurs

Research involving two Monash palaeontologists has produced the first life history reconstructions of the small plant-eating dinosaurs from Victoria, Australia.

A study published this week in the journal Scientific Reports examines the bone tissue microstructure of these ‘hypsilophodontid’ dinosaurs helps to better understand the lives of dinosaurs that lived inside the Antarctic Circle more than 105 million years ago.

“These little dinosaurs would have dealt with prolonged periods of darkness and mean annual temperatures near freezing, and certainly below freezing in the winter,” said one of the study authors, Dr Patricia Vickers-Rich, an Emerita Professor at the Monash School of Earth, Atmosphere and Environment. The hypsilophodont dinosaur. Credit: Dr Peter Trusler

The hypsilophodont dinosaur. Image credit: Dr Peter Trusler

The international research team from Oklahoma State University, Museums Victoria, Swinburne University of Technology and Monash studied fossils from 17 dinosaur specimens.

“An examination of the bone microstructure of these hypsilophodontid fossils revealed many characteristics of their growth, which could not be obtained through morphological examination alone,” Dr Holly Woodward, lead author from Oklahoma State University pointed out.

Rings in the bone, similar in appearance to tree rings, helped determine individual ages of the little dinosaurs studied.

Bone fiber orientation, blood vessel density, and the amount of bone between growth rings, was used to determine annual growth rates.

Bone histology revealed that, in general, growth was most rapid during the first three years of life, and when the dinosaurs were fully grown in five to seven years, they were the size of small wallaby or fully grown turkey.

“The hypsilophodontid samples were recovered from two localities in Australia, along the south Victoria coast, geologically separated by about 12 million years,” Dr Tom Rich from Museum Victoria/Monash University, noted.

Woodward further noted “However, the trend of rapid growth for three years followed by adult body size between five and seven years, was the same across the two samples.”

The tibia (shin-bone) of one hypsilophodontid individual in the sample had clearly suffered from a pathologic condition known as osteomyelitis (the oldest example known of this condition). Histologic examination revealed the cause of this pathology was most likely a broken bone, which then became infected.

Counting the growth rings preserved in this tibia prior to the formation of the pathologic bone, the team was able to place the timing of the injury as having occurred when this individual was approximately four years old.

The team was also able to estimate how long this little dinosaur lived and how it dealt with the injury: histologic examination of the unaffected femur (thigh bone) of this individual demonstrates that it survived with the injury and pathology for three more years.

”Further investigations of this unique sample will continue to shed light on how these little dinosaurs thrived in high latitudes and under the most stressful of environments during a time when dinosaurs flourished on planet Earth,” Dr Vickers-Rich said.

Silvia Dropulich Marketing, Media and Communications Manager, Science

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