A bunch of bones doesn't make a gang of bloodthirsty tyrannosaurs | Brian Switek

Tyrannosaurs are superb nightmare fuel. Exquisitely adapted for catching, killing and crunching other dinosaurs, they were among the most formidable predators ever, and now University of Alberta palaeontologist Philip Currie has proposed an even more frightening twist to tyrannosaur behaviour. The tyrants were not lone marauders, Currie suggests, but coordinated pack hunters.

Currie's hypothesis is presented in an absurdly hyped mass media package under the heading Dino Gangs. In its synopsis, the book Dino Gangs calls Currie's hypothesis "groundbreaking" three times in nearly as many sentences. The trailer for the documentary tie-in – aired on Discovery UK last month – doesn't hold back on the sensationalism, either, closing with the nonsequitur "If dinosaurs hadn't become extinct, would gangs of killer tyrannosaurs now rule the world?"

It should surprise no one that such nauseating hype emanates from Atlantic Productions. This is the same media company which, in 2009, pedalled exaggerated claims that a beautifully preserved fossil primate nicknamed "Ida" was "The Link" to our early simian ancestry. (As was immediately recognised by fossil primate experts, Ida was more closely related to lemurs than to us). And, as with Ida, the publicity blitz surrounding gangs of bloodthirsty tyrannosaurs has two parts: the media fluff, and the actual science.

The idea that some dinosaurs were cooperative predators is not new. Images of pack-hunting dinosaurs have been popular since multiple individuals of the sickle-clawed raptor Deinonychus were found entombed in a quarry with the bones of the herbivorous dinosaur Tenontosaurus in the 1970s, and the intelligent, cooperative Velociraptor – modeled upon Deinonychus – kept the heroes of Jurassic Park running in fear during the final act of the 1993 blockbuster (not to mention two sequels).

Social tyrannosaurs have been considered before, as well. Currie has been writing papers on pack-hunting tyrants for more than a decade.

Currie's hypothesis originated in a brilliant bit of fossil detective work. Over a century ago the famous fossil collector Barnum Brown discovered multiple specimens of the tyrannosaur Albertosaurus in the Late Cretaceous rock of Canada's Dry Island Buffalo Jump Provincial Park. Rather than fully excavate the rich site, however, Brown only collected a smattering of fossils before leaving.

Thanks to old notes and photographs, Currie relocated the quarry in 1998. Excavation yielded the remains of at least a dozen Albertosaurus of different ages. Currie speculated that they belonged to a social group with complex hunting behaviour, and in 2000 he published a paper "Possible evidence of gregarious behavior in tyrannosaurids" in which he imagined that the leggy, lightly built juvenile tyrannosaurs drove prey towards waiting adults. (On the basis of other bone beds, Currie has also proposed that the tyrannosaur Daspletosaurus and a very distantly related predator – a carcharodontosaur from Argentina named Mapusaurus – may have been social hunters.)

In Dino Gangs the press release, the book, and the documentary, though, the tyrannosaur Tarbosaurus is the star. The media materials say multiple Tarbosaurus specimens were found in relatively close proximity by the Korea-Mongolia International Dinosaur Project between 2006 and 2010. At one particular site, which is the peg for all the hubbub, six Tarbosaurus of different ages were purportedly found in close association.

No scientific paper has been published about the Tarbosaurus sites. The Dino Gangs media package is science by press release – studies of the sites have not yet been completed and communicated, yet sensational conclusions have been funneled to news sources that have credulously repeated assertions unconstrained by the actual data.

Nevertheless, even without the essential technical details of the Tarbosaurus sites, the characteristics of the Albertosaurus quarry and other dinosaur bonebeds provide plenty of reason to question the Dino Gangs hype. As Currie himself noted in a webchat promoted by Discovery UK – in which I also participated – "In fact, it really is only possible to interpret the Tarbosaurus sites in light of the Albertosaurus, Mapusaurus, Daspletosaurus and other discoveries."

Last year Currie and co-author David Eberth of Canada's Royal Tyrrell Museum published a paper "On gregarious behavior in Albertosaurus" in a special, all-Albertosaurus issue of the Canadian Journal of Earth Sciences. While Currie's notion of cooperative tyrannosaurs was entertained, the paper also noted that large numbers of animals are often brought together under harsh conditions, such as drought or flood. The fact that there is geological evidence for devastating local flooding at the site may indicate that the Albertosaurus were corralled into a small area before death.

There was no reason to automatically take the association of the bones as evidence of social behavior. Even what seemed to be the best evidence for gregarious tyrannosaurs is ambiguous.

Such is the trouble with bonebeds. Just because the skeletons of animals are found near each other does not necessarily mean that the creatures were together when they died or were socialising. About two hours' drive southeast from my apartment in Salt Lake City, Utah, there is a rich Jurassic dinosaur site known as the Cleveland-Lloyd Dinosaur Quarry. The jumbled remains of more than 44 individual Allosaurus specimens of different ages have been found here – they greatly outnumber the herbivores in the quarry – yet the proximity of these dinosaurs to each other does not mean that massive packs of Allosaurus terrorised the landscape. Cleveland-Lloyd probably was a predator trap which killed and preserved a large number of Allosaurus over an unknown stretch of time.

Simply put, bones alone are not enough to reconstruct dinosaur behaviour. The geological context in which those bones are found – the intricate details of ancient environments and the pace of prehistoric time – are essential to investigating the lives and deaths of dinosaurs. In the case of the Tarbosaurus sites, we need to know how each site formed, when each animal died, and if there were any local conditions that might have caused animals to assemble in a small area.

Similar caveats are aired in the Dino Gangs book and documentary, but, while I must credit the media masterminds behind the package for including dissenting voices, the arguments of the sceptical scientists are not taken seriously. Both the book and documentary record the search for evidence in support of Currie's hypothesis, and details are often spun in Currie's favor even when the evidence is contradictory or ambiguous.

In Dino Gangs the book, which reads like a bland transcript of the documentary, Currie visits animal locomotion specialist John Hutchinson at the Royal Veterinary College in Hatfield, England. Hutchinson explains that young tyrannosaurs were probably more agile and "bouncy" than adults, but whether they could truly run faster – acting as fleet-footed scouts as Currie suspects – is not clear. Yet the rest of the book considers Hutchinson's findings as a confirmation that Currie was correct.

Details of Tarbosaurus brain anatomy are spun in a similar way. Lawrence Witmer, an expert on dinosaur brains and soft-tissue anatomy at Ohio University, explains that there's no definite indicator of pack-hunting behaviour in the brain of Tarbosaurus – there is no "social lobe" to look at – only to have the book's author write "Currie prefers to reverse the line of enquiry: to ask whether there's anything in the brain to say that tyrannosaurs could not have complex social behavior."

The answer is no. Pack hunting remains a possibility, albeit one that has yet to be supported by hard evidence, but this short passage gives away the entire tone of the media campaign. The question is not "Were these dinosaurs social, and how can we know?" but "What evidence already exists that will support our desired image of dinosaur behaviour?"

Hence science is falsely shown as the search for only the data that will support preconceived conclusions, rather than an ongoing interrogation of nature in which the evidence does not always support what we had hoped or expected.

Tyrannosaurs may have lived in social groups, or they may not, and this uncertainty makes it all the more important to carefully weigh all the available evidence, not just that in favour of the sexiest idea. This is all the more unfortunate because, although he was there to promote tyrannosaur packs, during the webchat Currie took more care to qualify what is and isn't known, and responded "We can speculate ... but nothing more" when asked about the tactics Tarbosaurus gangs might use to stalk and attack prey.

When palaeontology is squeezed through the mass-media filter, scientific uncertainty is too often replaced by a ridiculous amount of hyperbolic assuredness that distorts how questions about nature are actually approached.

I would be thrilled if palaeontologists discovered compelling evidence that tyrannosaurs were social hunters. A trackway preserving the footsteps of several individuals moving in the same direction at the same time would be excellent. But until then, tableaus of tyrannosaur families dining together must remain tantalisingly speculative parts of prehistory.