Deinocheirus (/ˌdaɪnɵˈkaɪərəs/ dy-no-ky-rəs) is a genus of large ornithomimosaur (ostrich dinosaur) that lived during the Late Cretaceous around 70 million years ago. In 1965, a pair of large arms, shoulder girdles, and a few other bones of a new dinosaur were first discovered in the Nemegt Formation of Mongolia. In 1970, this specimen became the holotype of the only species within the genus, Deinocheirus mirificus; the genus name is Greek for "horrible hand". No further remains were discovered for almost fifty years, and its nature remained a mystery. Two more complete specimens were described in 2014, which shed light on many aspects of the animal. Parts of these new specimens had been looted from Mongolia some years before, but were repatriated in 2014.
Deinocheirus was an unusual ornithomimosaur, the largest of the clade at 11 m (36 ft) long, and weighing 6.36 t (14,000 lb). Though it was a bulky animal, it had many hollow bones which saved weight. The arms were among the largest of any bipedal dinosaurs at 2.4 m (7.9 ft) long, with large, blunt claws on its three-fingered hands. The legs were relatively short, and bore blunt claws. Its vertebrae had tall neural spines that formed a "sail" along its back. The tail ended in pygostyle-like vertebrae, which indicate the presence of a fan of feathers. The skull was 1.024 m (3.36 ft) long, with a wide bill and a deep lower jaw, similar to those of hadrosaurs.
The classification of Deinocheirus was long uncertain, and it was initially placed in the theropod group carnosauria, but similarities with ornithomimosaurians were soon noted. After more complete remains were found, Deinocheirus was shown to be a primitive ornithomimosaurian, most closely related to the smaller genera Garudimimus and Beishanlong, together forming the family Deinocheiridae. Members of this group were not adapted for speed, unlike other ornithomimosaurs. Deinocheirus is thought to have been omnivorous; its skull shape indicates a diet of plants, fish scales were found in association with one specimen and gastroliths were also present in the stomach region of the specimen. The large claws may have been used for digging and gathering plants. Bite marks on Deinocheirus bones have been attributed to the tyrannosaurid Tarbosaurus.
When Deinocheirus was only known from the original forelimbs, its taxonomic relationship was difficult to determine, and several hypotheses were proposed. Osmólska and Roniewicz initially concluded that Deinocheirus did not belong in any already named theropod family, so they created a new, monotypic family Deinocheiridae, placed in the infraorder Carnosauria. This was due to the large size and thick-walled limb bones, but they also found some similarities with Ornithomimus, and, to a lesser extent, Allosaurus. In 1971, John Ostrom first proposed that Deinocheirus belonged with the Ornithomimosauria, while noting that it contained both ornithomimosaurian and non-ornithomimosaurian characters. In 1976, Rhinchen Barsbold named the order Deinocheirosauria, which was to include the supposedly related genera Deinocheirus and Therizinosaurus. A relationship between Deinocheirus and the long-armed therizinosaurs was supported by some later writers, but they are not considered to be closely related today.
The distinct shape of the skull shows that Deinocheirus had a more specialised diet than other ornithomimosaurs. The beak was similar to that of ducks, which indicates it may have likewise foraged in water, or browsed near the ground like some sauropods and hadrosaurs. The attachment sites for the muscles that open and close the jaws were very small in comparison to the size of the skull, which indicates Deinocheirus had a weak bite force. The skull was likely adapted for cropping soft understorey or water vegetation. The depth of the lower jaw indicates the presence of a large tongue, which could have assisted the animal in sucking in food material obtained with the broad beak when foraging on the bottom of freshwater bodies.
More than 1,400 gastroliths (stomach stones, 8 to 87mm in size) were found among the ribs and gastralia of specimen MPC-D100/127. The ratio of gastrolith mass to total weight, 0.0022, supports the theory that these gastroliths helped the toothless animals in grinding their food. Features such as the presence of a beak and a U-shaped, downturned jaw, are indicators of facultative (optional) herbivory among coelurosaurian theropods. In spite of these features, fish vertebrae and scales were also found among the gastroliths, which suggests that it was an omnivore. Ornithomimosaurs in general are thought to have fed on both plants and small animals.
Various feeding behaviours were proposed before more complete remains of Deinocheirus were known, and it was early on envisioned as a predatory, allosaur-like animal with giant arms. In their original description, Osmólska and Roniewicz found that the hands of Deinocheirus were unsuited for grasping, but could instead have been used to tear prey apart. In 1970, the Russian paleontologist Anatoly Konstantinovich Rozhdestvensky compared the forelimbs of Deinocheirus to sloths, leading him to hypothesise that Deinocheirus was a specialised climbing dinosaur, that fed on plants and animals found in trees. In 1988, Gregory S. Paul instead suggested that the claws were too blunt for predatory purposes, but would have been good defensive weapons. While attempting to determine the ecological niches for Deinocheirus and Therizinosaurus in 2010, Phil Senter and James H. Robins suggested that Deinocheirus had the largest vertical feeding range due to its hip height, and specialised in eating high foliage.
Deinocherius in Land Before Time
Deino, the main antagnoist of the Greatest Adventure Trilogy, is a Dienocherius. He is called Fanged Flattooth in dino talk. His diet is different from actual Deinocherius, which the only meat it ate was insects and small animals and fish, to include other dinosaurs and also eggs.