Tuesday, May 29, 2012

The Killer Dinosaurs Of South-Eastern Australia

At least seven different killer dinosaurs once lived in what is now south-eastern Australia, a new study has found.

Research published in PLoS ONE describes the findings of scientists and volunteers from Monash University and Museum Victoria who uncovered a higher than expected biodiversity of meat-eating, theropod (bird-like) dinosaur fossils from between 105 and 120 million years ago.

A summary cladogram (evolutionary tree) of the therapod dinosaurs, showing the relationships between the major groups within the suborder Therapoda.
Credit: Benson et al. PLoS, doi:info:doi/10.1371/journal.pone.0037122.g002

Honorary Research Fellow Dr Tom Rich has lead the team collecting dinosaur fossils from the Otway and Stzelecki Ranges of south Victoria for 30 years with colleagues Lesley Kool, Dave Pickering and Professor Pat Vickers-Rich.

The team is associated with both Monash University’s School of Geosciences and Museum Victoria.

“We had not expected to find fossils from such a large range of dinosaur species in this area. The fossils we have collected range from tiny, cat-sized killers to Australia’s version of T. Rex, a nine-metre-long predator with powerful arms and razor-sharp claws,” Dr Rich said.

“In total 1500 isolated bones and teeth of various kinds of dinosaurs have been found in Victoria, Australia so far. Their meaning is only beginning to be unravelled by detailed study and comparisons with other fossils world-wide.”

At the time these dinosaurs ruled, southern Australia was part of the Antarctic Circle. Despite the cold, there was a high diversity of small predators, similar to the Velociraptor, featured in ‘Jurassic Park’.

Theropods are a group of mostly carnivorous dinosaurs that walked on two legs and had three-toed feet. Included among the theropods are the infamous T.rex, the small and agile Deinonychus, the feathered Archaeopteryx and modern birds. Tom and his colleagues have been pulling theropod fossils out of Victoria's coastline deposits since the 1970s and in this review, they considered 37 bones and over 90 individual teeth. They conclude that the local Cretaceous theropod fauna comprised nine major groups (or taxa), including allosauroids, tyrannosauroids, spinosauroids and the recently-discovered ceratosaur.

Artistic rendering of a  ceratosaur. The ceratosaur fossil was found in San Remo, a seaside town near Melbourne proves this is not the case.
Credit: Brian Choo/Museum Victoria

“One of the reasons for the success of small, theropod dinosaurs may be their warm-blood. As close relatives of birds, they had feathery insulation which helped maintain high body temperatures,” Dr Rich said.

“The cool, damp climate may also explain the discovery of the same dinosaur species in both Australia and the northern continents.”

The isolation of Gondwana and Australia from the rest of the world, and the unique conditions here, did help shape a unique assemblage at the species level. During the early Cretaceous, Australia was still attached to Antarctica and was much closer to the South Pole than it is now. Earth's climate was much warmer, the poles were free of icecaps and Victoria and Antarctica were covered in lush, ferny temperate forests. Long periods of winter darkness and extended summer daylight influenced the evolution of endemic dinosaurs whereas in other parts of the world, their distant relatives were contending with quite different environments.

Approximate position of Australia 120 million years ago during the Cretaceous era. 
Australia's position near the South Pole 120 million years ago 
Image: Ron Blakey. Altered by Cally Bennet and Fons VandenBerg
Source: Colorado Plateau Geosystems 

The study released in PLoS ONE by University of Cambridge researchers is focused on the discovery of these meat-eating theropod dinosaurs.

Birds evolved from a group of small theropod dinosaurs. Fossils of animals intermediate between birds and dinosaurs like Archaeopteryx show a combination of features from both groups. Archaeopteryx lived about 150 million years ago. It had a bony tail, a toothed jaw like a dinosaur and a wishbone like a bird. This reconstruction shows what it might have looked like.

Model of ArchaeopteryxCast of Archaeopteryx
Credit: Museum Victoria

A fossil of Archaeopteryx discovered in 1861 gave important support to the theory of evolution, as an example of an intermediate form between dinosaurs and birds.
Dr Roger Benson, from the University of Cambridge, said the study reports new discoveries and rationalises previous investigations.

Contacts and sources:
Monash University
Museum Victoria

Citation: Theropod Fauna from Southern Australia Indicates High Polar Diversity and Climate-Driven Dinosaur Provinciality

Roger B. J. Benson 1,2*, Thomas H. Rich 3,4, Patricia Vickers-Rich 3,4, Mike Hall 3

1 Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom, 2 Department of Earth Sciences, University College London, London, United Kingdom, 3 School of Geosciences, Monash University, Melbourne, Australia, 4 Palaeontology Department, Museum Victoria, Melbourne, Australia

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