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Fossil find the tip of the iceberg: - scientists.

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Postby rath » Wed Jul 14, 2010 11:06 pm

July 15, 2010
3 hours 16 minutes ago

Australian researchers have unearthed a treasure trove of fossils in outback Queensland that contains individuals of a 'long-legged wombat-like' species ranging from birth to adulthood.

A North Queensland cave could house a paleontological treasure trove, with scientists predicting that more than 60 new species are preserved in the limestone floor.

Hundreds of fossils of the extinct, wombat-like marsupial Nimbadon have been discovered by paleontologists at the site in Riversleigh, with scientists using the skulls of 26 animals to trace its life cycle.

Karen Black of the UNSW School of Biological, Earth and Environmental Sciences said the team of researches had only scratched the surface of the cave's floor

The significant discovery reveals how these animals grew and highlights the similarities between today's marsupials and their ancient ancestors.

The discovery appears today in the Journal of Vertebrate Paleontology.

A little over 15 million years ago, Australia was covered in a lush tropical rainforest. It was also home to a group of marsupials, known as Nimbadon lavarackorum.

"I guess you'd describe it as a long-legged wombat, [but] it's not from the wombat family," says University of New South Wales researcher Dr Karen Black.

"It's from a family known as diprotodontids and they were the common large herbivores roaming around Australia for the last 25 million years."

Dr Black has been leading a team of researchers working at a site known as AL90 in the Riversleigh World Heritage area.

She says the area is well known as a fossil hotspot, containing the fossilised remains of animals as far back as 25 million years ago. But for researchers this is particularly interesting.

"This is a fantastic and incredibly rare site," she said.

"The exceptional preservation of the fossils has allowed us to piece together the growth and development of Nimbadon from baby to adult."

So far the researchers have recovered 26 Nimbadon skulls ranging in age from a suckling young to a fully-grown adult.

Dr Black says to find such a large collection of the one animal suggests it may have moved in groups, or mobs, similar to the modern-day grey kangaroo.

"The animals appear to have plunged to their deaths through a vertical cave entrance that may have been obscured by vegetation and acted as a natural pit-fall trap," she said.

Skull growth

Dr Black says the skulls reveal that the animals grew in a very similar way to modern-day marsupials.

"When you look at the skulls, the bones that surround the teeth, the upper and lower jaw, and of the roof of the mouth are quite advanced in their development compared with the rest of the bones in the skull," she said.

"This is related to the fact that marsupials when they are born, they are born at a very early age - usually less than one month old. They need to make their way to the mother's teat by themselves and attach to the teat and start suckling.

"Later when the animal begins to chew leaves you can see different features. The back of the skull tends to develop and the area of muscle attachment [becomes] more developed."

Study co-author, Professor Mike Archer says as the animal grew, large bony cavities developed in the skull preventing the brain from expanding.

"We found that its brain was quite small and stopped growing relatively early in its life," he said.

"We think it needs a large surface area of skull to provide attachments for all the muscle power it required to chew large quantities of leaves, so its skull features empty areas, or sinus cavities.

"Roughly translated, this may be the first demonstration of how a growing mammal 'pays' for the need to eat more greens - by becoming an 'airhead'."
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