Deinocheirus mirificus
Deinocheirus mirificus is one of the strangest dinosaurs ever unearthed. It reached roughly eleven metres in length and is estimated to have weighed between five and seven tonnes, making it by far the largest known ornithomimosaur – the group usually nicknamed "ostrich dinosaurs".
Deinocheirus
Deinocheirus mirificus
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Quick facts
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Weight
5000–7000 kg
Length
10–12 m
Diet
Omnivore
Period
Cretaceous
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5000–7000 kg
10–12 m
Cretaceous
Bipedal
3.5–5 m
Omnivore
4 recorded fossil finds in Mongolia. First described in 1969 by Kielan-Jaworowska.
Sites and counts from the Paleobiology Database
The timeline shows the whole age of dinosaurs – and how much time has passed since. The glowing part is when Deinocheirus lived.
million years ago
Lived 71–69 million years ago
If the whole age of dinosaurs were a single day, Deinocheirus lived at 23:29.
Chapter • Meet the dinosaur
Deinocheirus mirificus is one of the strangest dinosaurs ever unearthed. It reached roughly eleven metres in length and is estimated to have weighed between five and seven tonnes, making it by far the largest known ornithomimosaur – the group usually nicknamed "ostrich dinosaurs". Its body was bulky and barrel-shaped, its back carried a tall hump or low sail formed by elongated neural spines, and its hind limbs were stout, with broad, blunt toes rather than the slender running legs of its relatives. The skull was almost a metre long, entirely toothless and ended in a wide, duck-like bill, while the arms measured about 2.4 metres and bore three blunt claws. Because close relatives such as Ornithomimus are preserved with feathers, researchers assume Deinocheirus was feathered too, at least in part, and its fused terminal tail vertebrae resemble a pygostyle – the same structure that anchors the tail fan in modern birds.
Chapter • Where it lived
Deinocheirus lived about 70 million years ago, in the late Cretaceous (Maastrichtian), in what is now Ömnögovi Province in southern Mongolia. Every known specimen comes from the Nemegt Formation, laid down in a landscape of broad floodplains, meandering rivers, wetlands and seasonal lakes – far wetter than the desert deposits beneath it. The holotype arms were excavated in 1965 at Altan Uul III by a Polish-Mongolian expedition, while the two far more complete skeletons were recovered in 2006 and 2009 at Altan Uul IV and Bugiin Tsav. It shared this environment with Tarbosaurus, Saurolophus, Therizinosaurus and Gallimimus, as well as turtles, crocodylians and fish that underline how water-rich the region was.
Chapter • Wild behavior
Cathemeral
Very little is known about the social life of Deinocheirus. The species is represented by just three individuals, all found separately, and there are no bonebeds or trackways indicating herding. Other ornithomimosaurs, such as Sinornithomimus from China, have been found in groups mixing juveniles and adults, so occasional gatherings are plausible for Deinocheirus as well – but that is an inference from relatives, not direct evidence.
The name means roughly "terrible hand": for almost fifty years the animal was known only from its arms.
Those arms are about 2.4 metres long, among the longest forelimbs of any bipedal dinosaur ever found.
More than 1,400 gastroliths – stomach stones for grinding plant food – were found in the gut region of one specimen.
Fish vertebrae and scales were mixed in with the stomach stones, direct evidence that Deinocheirus ate fish.
Its broad, toothless bill resembles a duck's and was probably suited to cropping and straining soft water plants.
The long neural spines along the back supported a hump or low sail, comparable to Spinosaurus but much lower.
The skull and a hand from the 2009 specimen were looted and smuggled out of Mongolia, and were only repatriated in 2014.
Despite its size, Deinocheirus was no super-predator but a slow-moving omnivore with small, blunt claws.
Chapter • Scientific place
Nature
Reviewed: 9/5/2026
Peer-reviewed description by Lee et al. (2014) whose phylogenetic analysis places Deinocheirus mirificus within Theropoda: Coelurosauria: Ornithomimosauria (Deinocheiridae).
Open sourceNature
Reviewed: 9/5/2026
Documents all known specimens and their Mongolian localities in the Upper Cretaceous Nemegt Formation, including the 1965 holotype site and the Altan Uul IV and Bugiin Tsav skeletons.
Open sourcePalaeogeography, Palaeoclimatology, Palaeoecology (Elsevier)
Reviewed: 9/5/2026
Peer-reviewed reconstruction of the Nemegt Formation palaeoenvironment as a wet, river- and floodplain-dominated landscape inhabited by Deinocheirus and its contemporaries.
Open sourceNatural History Museum, London
Reviewed: 9/5/2026
Museum Dino Directory listing of omnivorous dinosaurs, the dietary category assigned to Deinocheirus on the basis of its gastroliths and preserved fish remains.
Open sourcePalaeogeography, Palaeoclimatology, Palaeoecology (Elsevier)
Reviewed: 9/5/2026
Extinct taxon; conservation status NE
Open sourceNatural History Museum, London
Reviewed: 9/5/2026
Authoritative museum overview of Deinocheirus covering its size, anatomy, age and classification, used as the shared reference for the sv, en, da and no description texts.
Open sourceNatural History Museum, London
Reviewed: 9/5/2026
Authoritative museum overview of Deinocheirus covering its size, anatomy, age and classification, used as the shared reference for the sv, en, da and no description texts.
Open sourceNatural History Museum, London
Reviewed: 9/5/2026
Authoritative museum overview of Deinocheirus covering its size, anatomy, age and classification, used as the shared reference for the sv, en, da and no description texts.
Open sourceNatural History Museum, London
Reviewed: 9/5/2026
Authoritative museum overview of Deinocheirus covering its size, anatomy, age and classification, used as the shared reference for the sv, en, da and no description texts.
Open source