The two plant-eating, four-legged sauropod species are new types of titanosaurs - the largest animals ever to walk the Earth.
"Clancy" (scientific name: Witonotitan wattsi) was a tall slender animal, while Matilda (Diamantinasaurus matildae) was more stocky and hippo-like.
Banjo and Matilda - possibly predator and his prey - were found buried together in a 98-million-year-old billabong, or stagnant pond.
A comparison of all three: "Matilda" (L), "Clancy" (C) and "Banjo" (R)
The findings have been published in the public access journal Public Library of Science One (PLoS One), and were announced by Queensland Premier Anna Bligh at the Australian Age of Dinosaurs Museum of Natural History in Winton.
She said the discoveries were a major breakthrough in the scientific understanding of prehistoric life in Australia.
Museum Victoria palaeontologist John Long described the fossils as "amazing".
The Sydney Morning Herald newspaper quoted him as saying that the creatures put Australia back on the international map of big dinosaur discoveries for the first time since 1981, when the unearthing of Muttaburrasaurus, a large four-legged herbivore that could rear up on two legs, was announced.
The new species will be part of the Australian Age of Dinosaurs Museum of Natural History under construction in Winton. It should be completed in 2015.
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