Deinocheirus is now considered by most paleontologists to be an ornithomimosaur, as the structure of its arms is similar to other dinosaurs of this group. This would make Deinocheirus by far the largest ornithomimosaur, weighing roughly 9,000 kg. Makovicky et al. pointed out that if Deinocheirus is an ornithomimosaur, it is a fairly primitive one, since it lacks some of the features typically seen in ornithomimosaurs. Kobayashi and Rinchen Barsbold added Deinocheirus to several recent cladistic analyses of theropods and were unable to resolve its exact relationships but noted some support for it as a possible ornithomimosaur.
However, over the decades, scientists have not always concurred about the placement of Deinocheirus within Dinosauria. Osmólska and Roniewicz created a new family for Deinocheirus, the Deinocheiridae. The family Deinocheiridae was initially placed in the infraorder Carnosauria, owing to the "gigantic size and thick-walled limb bones" but Osmólska and Roniewicz also speculated that it possibly "constitutes a link between Carnosauria and Coelurosauria". Within Carnosauria, the family Deinocheiridae was tentatively assigned to the superfamily Megalosauroidea, basically because it was obviously not a tyrannosauroid (tyrannosaurids having greatly reduced forelimbs). Other paleontologists (such as those as the American Museum of Natural History) have concluded that Deinocheirus is a therizinosaur, though this is a minority opinion.
Early work generally envisioned Deinocheirus as a carnivore that used its long forelimbs "in tearing dead or weakly agile prey asunder" (Osmólska & Roniewicz 1970: 15). Lambert supported this view, describing the clawed hands of Deinocheirus as "horrifying weapons for attacking dinosaurs of almost any size ... capable of ripping open a sauropod's soft underbelly". Gregory S. Paul disagreed, suggesting that the claws are too blunt for killing but would have been good defensive weapons. The Russian paleontologist Rozhdestvensky compared the forelimbs of Deinocheirus to sloths, leading him to hypothesize that Deinocheirus was a specialized climbing dinosaur, that fed on fruits and leaves and perhaps also eggs and any small animals found in trees. Rozhdestvensky imagined Deinocheirus with the trunk and hind limbs no longer than the fore limbs, but there is no hard evidence for this and the climbing hypothesis has not received much support from other scientists.
Bizarre Dinosaurs: Some Very Strange Creatures and Why We Think They Got That Way.(Young adult review)(Book review)
Jan 01, 2009; Bizarre Dinosaurs: Some Very Strange Creatures and Why We Think They Got That Way by Christopher Sloan. 2008. 32pp. $16.95....