But some experts remain sceptical. They say that the sites could have been predator traps, where animals sank into sticky molten tar bubbling up from deep within the Earth.
The giant herbivores would have lived, walked and died together, based on evidence gleaned from dinosaur graveyards and fossilised footprints.
But now palaeontologist Dr Phil Currie, from the Royal Tyrell Museum, Alberta, Canada, has discovered two fossil bone-beds, buried for millions of years, showing groups of massive carnivorous dinosaurs.
In an interview for the BBC Television series Horizon, he said the new finds were good evidence that huge meat-eating dinosaurs did hunt together in packs.
'Social groups'
The first site, in Alberta, Canada, contained the bones of at least 12 large carnivorous tyrannosaurs, including young and old.
Remains of at least six giant meat-eaters were found at a second bone-bed in Patagonia, South America.
Dr Currie told the BBC: "It seems to me that we have very convincing evidence that large meat-eating dinosaurs formed these social groups where the young and the old worked together, hunted together and lived together."
But some experts remain sceptical. They say that the sites could have been predator traps, where animals sank into sticky molten tar bubbling up from deep within the Earth.
Or floodwaters spreading across the plains could have washed together the remains of several unrelated dinosaurs.
Buried in the same place millions of years ago, the bones might look like a pack when unearthed today.
Angela Milner of London's Natural History Museum said: "A collection of bones in a bone-bed doesn't automatically mean we're looking at a collection of animals that lived together.
"Sometimes bone beds accumulate from large areas of the land where floods have brought all kinds of animal remains together and mixed them up."
The two new discoveries also raise another intriguing possibility. In most parts of the world, the largest meat-eaters and the largest herbivores never walked
the Earth at the same time.
The giant long-necked plant-eating dinosaurs died out in the northern continents around 100 million years ago.
But plant-eaters like the massive Argentinosaurus lived on in the South. And recent fossil finds suggest that fearsome predators like Giganotosaurus, bigger than Tyrannosaurus Rex, were also around at the same time in South America.
Bones of the two giants have been found only 80 kilometres apart.
Which means that in prehistoric South America, because of a quirk of evolution, the largest meat-eaters could have fought the largest herbivores in a Clash of the Titans.