Temporal range: Late Cretaceous, 71–69Ma
|Holotype fossil on display in CosmoCaixa, Barcelona|
Osmólska & Roniewicz, 1970
|Species:||† D. mirificus|
Osmólska & Roniewicz, 1970
Deinocheirus (// DY-no-KY-rəs; Greek: 'terrible hand') is a genus of very large ornithomimosaur theropod dinosaur, which lived in what is now southern Mongolia, during the late Cretaceous Period (Nemegt Formation, dating to around 70 million years ago).
Discovery and naming
The first known fossil remains are a single pair of massive forelimbs and the remains of some ribs and vertebrae. They were found on 9 July 1965 during a Polish-Mongolian expedition to the Gobi by Professor Zofia Kielan-Jaworowska at the Altan Ula III site in Ömnögovi Province. Kielan-Jaworowska published the find in 1966.
Deinocheirus was named by Halszka Osmólska and Ewa Roniewicz in 1970. The type species and only named species is Deinocheirus mirificus. The generic name is derived from Greek deinos (δεινός), meaning "horrible", and cheir (χείρ), meaning "hand". The specific name, mirificus, comes from Latin, meaning "unusual" or "peculiar," and was chosen for the "unusual structure of the forelimbs."
The holotype specimen, ZPal MgD-I/6, was discovered on the desert surface in sandstone dating to the early Maastrichtian. It consists of a partial, disarticulated skeleton, most parts of which had already weathered away at the moment of discovery. Both forelimbs excluding the right claws, the complete shoulder girdle, centra of three dorsal vertebrae, five ribs, gastralia and two ceratobranchialia, supporting neck bones, could still be recovered.
Additional fossils, including fragments of gastralia (belly ribs) belonging to the same specimen, were later found by teams re-examining the original fossil site. Some of these bones contained bite marks made by the contemporary tyrannosaurid species, Tarbosaurus bataar, and showed evidence consistent with scavenging. The possibility that the carcass was scavenged by tyrannosaurs may explain why the specimen was preserved in a scattered, disassociated state.
In 2014, palaeontologists described two new specimens of Deinocheirus discovered in Mongolia in 2006 and 2009. One specimen, MPC-D 100/127, is even larger than the holotype, with a left forelimb 6% longer. The other specimen, MPC-D 100/128, is smaller, and the two together provide a nearly complete skeleton. Both skeletons had been poached by illegal fossil hunters. The skull and foot bones of MPC-D 100/127 were sold to Japan and resold to Germany. They were in 2011 obtained by the French fossil trader François Escuillé who donated them to the Royal Belgian Institute of Natural Sciences: they were repatriated to Mongolia in May 2014.
The best-preserved parts of Deinocheirus are its forelimbs, which measured 2.4 m (8 ft) long — a 938 mm humerus, 688 mm ulna and 770 mm hand — including up to 19.6 cm (8 in) long recurved claws. Each scapulocoracoid of the shoulder girdle has a length of 153 centimetres. The neck must also have been massive: each half of the paired ceratobranchialia measures 42 centimetres.
The gigantic size of these skeletal elements has generated much speculation about the magnitude of the animal as a whole. Osmólska and Roniewicz thought it could be best compared with the Ornithomimosauria, as the structure of its arms is similar to the members of this group. Should Deinocheirus itself be a member, this would make it by far the largest ornithomimosaur, indeed, one of the largest theropods. The describers estimated its size to be equal to the largest specimens of Tyrannosaurus. In 1988 its weight was estimated by Gregory S. Paul to have been between six and twelve tonnes. Later its weight was confirmed as roughly 9,000 kg (20,000 lb). In 2010 Paul revised this to a length of ten metres and a weight of two tonnes.
In 2010, Phil Senter and H.J. Robins attempted to estimate the total height at the hip of Deinocheirus. By studying more completely known theropods, they concluded that the length of the scapula (shoulder blade), better than that of the humerus (upper arm bone), could be used to accurately predict hip height. Using the equation established by comparing a range of theropods, Senter and Robins determined that Deinocheirus likely measured 3.3 m (11 ft) to 3.6 m (12 ft) tall at the hip. This would place it as possibly the tallest known theropod, taller than any contemporary predators such as Tarbosaurus. Though the arms of Deinocheirus have a considerable absolute size, being the longest of any known theropod with the exception of Therizinosaurus, they are not very long relative to the shoulder girdle, the ratio being less than that with most ornithomimosaurs. The shoulder-blade is long and narrow. The humerus is relatively slender. The ulna and radius too are elongated and not very firmly connected to each other in a syndesmosis. The metacarpus is long compared to the fingers. The hand had good mobility relative to the lower arm but was capable of only a limited flexing motion, unable to close in grasping. The fingers are about equal in length to each other, the first being the stoutest and the second the longest. Only the claw of the left second finger has been preserved in its entirety; it has a diameter of 196 millimetres and a length along its outer curvature of 323 millimetres.
Reports of the new specimens, when they were still formally undescribed, showed that the animal had a hump on its back and a skull that superficially resembled a cross between an ornithomimosaur and a hadrosaur.
In 2014, a new reconstruction based on the two nearly complete specimens was published in Nature. It showed a bipedal, relatively upright-walking animal, sporting on its back tall neural spines up to 8.5 times the centrum height, almost attaining the highest ratio seen in Spinosaurus. The spines were probably specialized to support the abdomen from the hips in view of the probable presence of an intricate system of interspinous ligaments. The back vertebrae were strongly pneumatic. The tail was relatively short and possibly featured a tail fan of feathers, supported by a pygostyle of at least two fused tail vertebrae. The toothless skull was elongated with a low snout, transversely expanded at its tip. The skull bone walls were rather thin, about six millimetres. The lower jaws were extremely deep. The specimen MPC-D 100/127 had an estimated body length of 11 metres (36 ft) and an estimated body mass of 6,358 kilograms (14,017 lb), and is the largest known ornithomimosaur. More than 1400 gastroliths were found inside the ribs and gastralia of Deinocheirus, along with fish remains. The stomach contents and ecomorphological features suggest that Deinocheirus was an omnivore.
Before the publication of the new reconstruction based on near-complete skeletal remains in 2014 which confirmed that Deinocheirus was indeed a large ornithomimosaur, scientists did not always agree about the placement of Deinocheirus within Dinosauria. While Kielan-Jaworowska had initially assigned the find to the Megalosauridae, 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, "faute de mieux", assigned to the superfamily Megalosauroidea, basically because it was obviously not a tyrannosauroid, which have greatly reduced forelimbs endowed with only two extremely small fingers.
Peter 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. Basal traits include the recurved claws, the low humerus/scapula ratio, the lack of syndesmosis, a short posterior process of the coracoid and the combined length of the second and third phalanx of the third finger being greater than the length of the third phalanx. Yoshitsugu 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. Derived traits include the short hand, a flat metacarpus and a relative elongation of the claws.
The cladogram below follows an analysis by Yuong-Nam Lee, Rinchen Barsbold, Philip J. Currie, Yoshitsugu Kobayashi, Hang-Jae Lee, Pascal Godefroit, François Escuillié & Tsogtbaatar Chinzorig (2014).
The paleobiology of Deinocheirus has been well-discussed over the past years, especially in the description of new material of the genus. Deinocheirus is presumably a megaomnivore on the basis of gastroliths preserved in its abdominal cavity, as well as a keratinous beak, fish remains in its stomach, and a downturned dentary. Deinocheirus was likely diurnal, as shown by the size of its sclerotic rings in comparison with its orbit.
ZPAL Mgd-I/6, the holotype of Deinocheirus mirificus, has abnormal pits, grooves and tubercles on the first and second phalanx of the left second finger that may be the result of injuries to the joint between the two bones.
Early work generally envisioned Deinocheirus as a carnivore that used its long forelimbs "in tearing dead or weakly agile prey asunder".:15 David 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". G.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 hindlimbs no longer than the forelimbs, but there is no hard evidence for this and the climbing hypothesis has not received much support from other scientists.
Paul in 1988 suggested a herbivorous lifestyle for Deinocheirus. It shared its habitat with several other giant, nine to thirteen meter long, herbivores uncovered in the Nemegt Formation, like the small titanosaur sauropod Opisthocoelicaudia, the hadrosaurs Saurolophus and Barsboldia, and the bizarre even longer-clawed Therizinosaurus. Trying to determine the respective niches for these animals Senter & Robins concluded that Deinocheirus due to its hip height had the largest vertical feeding range of them all, specialising in eating high foliage. Paul in 1988 had proposed it would have used its long neck to reach into trees and rip leaves, the arms assisting in pulling down branches. The rock facies of the Nemegt formation suggest the presence of stream and river channels, mudflats, and shallow lakes. Sediments also indicate that there existed a rich habitat, offering diverse food in abundant amounts that could sustain massive Cretaceous dinosaurs.
Most recently, it was hypothesized that Deinocheirus was in fact omnivorous. The new material of it described in 2014 included stomach contents, as well as gastroliths which would have assisted with digestion. Lee et al. found that the ratio of gastrolith mass to total weight, 0.0022, was in support of the gastroliths being used for grinding up harder plant and animal material, in a gastric mill. Also supporting an omnivorous diet are the facts that Deinocheirus was toothless, and instead had a rhamphotheca or beak, a downturned dentary, edentulous jaws, a U-shaped dentary, and a dorsally convex dentary. Fish ribs and scales show that Deinocheirus was not exclusively herbivorous, at least occasionally eating other animals. The claws were not found to be weapons, instead likely being used for digging up and gathering plants.
Lee et al. identified that Deinocheirus would definitely not have possessed a strong bite force, unlike the contemporaneous tyrannosaurids. The teeth and skull of Deinocheirus were likely evolved for cropping the soft understory plants along riversides. The anatomy of the lower jaw is shaped for a large tongue, which most likely would have assisted in the grasping and manipulating the food consumed by Deinocheirus.
In 2012, Phil R. Bell, Philip J. Currie, and Yuong-Nam Lee identified marks of predation of a specimen from Deinocheirus. Bite marks from Tarbosaurus were found on the Gastralium (lower ribs) of Deinocheirus. The size and shape of the marks made by teeth match Tarbosaurus more than any other tyrannosaur from the region, so it is assumed that it was what bit the Deinocheirus. Five types of marks were analyzed, punctures, gouges, striae, fragmentary teeth, and combinations of the above marks. As only 2% of all theropod feeding trances are bite marks, and as the marks are found on a rare species, the identification of the pathologies are very important.
The known Deinocheirus fossils have been recovered from the Nemegt Formation in the Gobi Desert of southern Mongolia. This geologic formation has never been dated radiometrically, but the fauna present in the fossil record indicate it was probably deposited during the early Maastrichtian stage, at the end of the Late Cretaceous about 70 million years ago. Within the habitat, Deinocheirus would have eaten small animals and plants, as well as fish like the ones preserved. This means that Deinocheirus, a 6.4 tonnes (6.3 long tons; 7.1 short tons) megaomnivore, would have had much competition, with the gigantic predatory tyrannosaurid Tarbosaurus, possibly a few humungous titanosaurs, and the other duck-billed creature, the saurolophine Saurolophus. The size of Deinocheirus may have helped it reach higher branches, and had access to more food without competition.
Nemegt sediments preserve large river channels and soil deposits that indicate a far more humid climate than those suggested by the underlying Barun Goyot and Djadochta Formations. However, caliche deposits indicate at least periodic droughts. Sediment was deposited in the channels and floodplains of large rivers. The rock facies of this formation suggest the presence of mudflats, and shallow lakes. Sediments also indicate that there existed a rich habitat, offering diverse food in abundant amounts that could sustain massive Cretaceous dinosaurs. Occasional mollusc fossils are found, as well as a variety of other aquatic animals like fish and turtles. Crocodilians included several species of Shamosuchus, a genus with teeth adapted for crushing shells. Mammal fossils are exceedingly rare in the Nemegt Formation, but many birds have been found, including the enantiornithine Gurilynia and the hesperornithiform Judinornis, as well as Teviornis, an early representative of the still-existing Anseriformes (waterfowl), a bird order. Scientists have described many dinosaurs from the Nemegt Formation, including ankylosaurids such as Tarchia, and pachycephalosaur Prenocephale. By far the largest predator known from the formation, adult Tarbosaurus most likely preyed upon large hadrosaurs such as Saurolophus and Barsboldia, or sauropods such as Nemegtosaurus, and Opisthocoelicaudia. Theropods include the small tyrannosaurid Alioramus, troodontids (Borogovia, Tochisaurus, Saurornithoides), oviraptorosaurs (Elmisaurus, Nemegtomaia, Rinchenia) or Bagaraatan, sometimes considered a basal tyrannosauroid. Other theropods, like the gigantic Therizinosaurus, may have been herbivorous, and ornithomimosaurs such as Anserimimus, Gallimimus.
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