Temporal range: Late Cretaceous, 71–69Ma
|Arms and shoulder blades of the holotype specimen 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 ornithomimosaurian dinosaur that lived in what is now southern Mongolia during the late Cretaceous period around 70 million years ago. The genus Deinocheirus contains one species, Deinocheirus mirificus.
Deinocheirus was long thought of as a very mysterious dinosaur, known only from a set of gigantic fossil arm bones. The discovery of more complete skeletons helped to solve this longstanding mystery, revealing a very strange, giant, bipedal omnivore. Though it had many of the typical skeletal features of its group, its overall appearance was very different from its relatives.
Deinocheirus was the largest ornithomimosaurian dinosaur; the largest known specimen (MPC-D 100/127) measured up to 11 m (36 ft) long, with an estimated weight of 6,358 tonnes (14,017,000 lb). The two other known specimens are smaller, the holotype (MPC-D100/18) by 6%, and the smallest (MPC-D100/128) by 74%. The size of Deinocheirus generated much speculation since it was first discovered. Osmólska and Roniewicz though that Deinocheirus best compared to ornithomimosaurians, while assuming similarities evolved convergently. It would have been by far the largest ornithomimosaurian, as they estimated that Deinocheirus would be equal in size to the larges specimens of Tyrannosaurus. In 1988, Gregory S. Paul estimated the weight of Deinocheirus to have been 6–12 t (5.9–11.8 long tons; 6.6–13.2 short tons). Later, a different study found its weight roughly 9 t (8.9 long tons; 9.9 short tons). In 2010, Paul revised his earlier estimate, giving Deinocheirus a length of 10 m (33 ft) and a weight of 2 t (2.0 long tons; 2.2 short tons). In 2010, Phil Senter and James H. Robins attempted to estimate the total hip height of Deinocheirus. By studying and analysing more completely known theropods, they concluded that the scapular length, could be used to accurately predict hip height better than the alternative of humeral length. Using the equation based on the analyzing of a range of different theropods, Senter and Robins determined that Deinocheirus was likely 3.3–3.6 m (11–12 ft) tall at the hip. This places Deinocheirus as the tallest known theropod, by extent much taller than any other contemporaries, such as Tarbosaurus and Therizinosaurus.
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, upper arm bone, is relatively slender. The ulna and radius, lower arm bones, too are elongate, 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, 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. The furcula was U-shaped. The hind limbs were relatively short, and the thigh bone was longer than the shin bone, as is common for large animals. The claw bones of the feet were blunt and broad-tipped instead of tapered, unlike other theropods.
The only known skull, belonging to the largest specimen, measures 1024 mm from the premaxilla at the front to the back of the occipital condyle. The skull was similar to those of other ornithomimosaurs in being low and narrow, but differed in that the snout was more elongated. It had a rounded, flattened beak, which would have been covered by keratin in life. The nostrils were turned upwards, and the nasal bone was a narrow strap, that extended up above the eye sockets. The outer diameter of the sclerotic rings in the eyes were small, 84 mm (3.3 in), compared to the size of the skull. The temporal fenestra openings behind the eyes were partially closed off by the jugal bones, similar to Gallimimus. The jaws were toothless and down turned, and the lower jaw was very massive and deep compared to the slender and low upper jaw. The lower jaw was closer in scale to that of tyrannosaurids than to other ornithomimosaurs. The snout flared outwards to the sides, which is similar to the duck-billed hadrosaurids.
The ten neck vertebrae were low and long, and become progressively shorter backwards from the skull. This resulted in a more s-curved neck than seen in other ornithomomisaurs, due to the larger skull. The neural spines of the twelve back vertebrae became increasingly longer from front to back, the last one being 8.5 times the height of the centrum part. This is almost the same as the highest ratio in the neural spines of the theropod Spinosaurus. The spines had a system of connecting ligaments, which were probably used to support the abdomen by attaching to the hips and hind legs, similar to a cable bridge. All the vertebrae were highly pneumatic (hollow), except for the atlas bone and the hindmost tail vertebrae. The back vertebrae were as pneumatic as those of sauropod dinosaurs. These adaptations can be correlated with gigantism. The six vertebrae of the sacrum were also tall and pneumatic, and all but the first one were fused together at the top. The hip was also partially pneumatic close to the sacral vertebrae. Part of the pelvis was hypertrophied (enlarged) compared to other ornithomimosaurs, to support the large weight of the animal w with strong muscle attachment. The tail of Deinocheirus ended in at least two fused vertebrae, which were described as similar to the pygostyle of oviraptorosaurian and therizinosauroid theropods. Ornithomimosaurs are known to have had pennaceous feathers, so this feature suggests that they possibly had a fan of feathers at the tail ends.
Before the description of more complete skeletal remains in 2014 which confirmed that Deinocheirus was a large ornithomimosaurian, scientists did not always agree about the placement of Deinocheirus relative to other dinosaurs. 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 had greatly reduced forelimbs and only two small fingers.
Peter Makovicky et al. pointed out that Deinocheirus was is a fairly primitive ornithomimosaurian, since it lacked some of the features typically seen in ornithomimids. Primitive 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.
A cladogram accompanying the 2014 description of more complete specimens found that Deinocheirus formed a clade with Garudimimus and Beishanlong, which were therefore included in the Deinocheiridae:
Deinocheiridae was defined to include all taxa with a more recent common ancestor with Deinocheirus mirificus than with Ornithomimus velox. The three members share various anatomical features in the limbs. The cladogram suggested that ornithomimosaurians diverged into two lineages in the Early Cretaceous, Deinocheiridae and Ornithomimidae. Unlike other ornithomimosaurians, deinocheirids were not built for running.
Deinocheirus was likely diurnal (active during the day), since the sclerotic rings of the eyes were relatively small in comparison with its skull length. The long neural spines and possible tail fan may have been used for display behaviour.
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. Another pathology is on the right seventh rib of Deinocheirus, a healed trauma showing the bone regrown.
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.
Within this ecosystem, Deinocheirus would have eaten plants and small animals, including fish. Deinocheirus, as a 6.4 tonnes (6.3 long tons; 7.1 short tons) mega-omnivore, may not have faced much competition. The size of Deinocheirus may have helped it reach higher branches, and had access to more food without competition from other large herbivores.
Deinocheirus appears to have been an omnivore. The specimens described in 2014 included fish ribs and scales as 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 flattened beak, toothless jaws, and a downturned, U-shaped lower jaw which was dorsally convex. The fish ribs and scales show that Deinocheirus was not exclusively herbivorous, at least occasionally eating other animals. The claws were probably not used as weapons, but instead for digging up and gathering plants. Lee et al. found that Deinocheirus did not have a strong bite force, unlike contemporary species of tyrannosaurid. The skull of Deinocheirus was likely adapted for cropping soft understory plants along riversides. The shape of the lower jaw indicates the presence of a large tongue, which most likely would have assisted in the grasping and manipulating the food consumed by Deinocheirus.
Further evidence for at least partial herbivory by Deinocheirus was published in a presentation for SVP 2014 in Berlin. The authors, including Pascaline Lauters and most of the authors from the earlier paper, analyzed the brain size and shape, and found that the Encephalization Quotient for Deinocheirus was 0.69. The brain was similar in shape to troodontids and birds, and the brain size implicates that Deinocheirus was a partial herbivore with a quotient comparable to sauropods, and much lower than predatory theropods.
Early work generally envisioned Deinocheirus as a carnivore that used its long forelimbs "in tearing dead or weakly agile prey asunder". 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 titanosaurian Opisthocoelicaudia, the hadrosaurs Saurolophus and Barsboldia, and the bizarre even longer-clawed Therizinosaurus. 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. 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.
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. The rock facies of the Nemegt formation suggest the presence of stream and river channels, mudflats, and shallow lakes. Such large river channels and soil deposits are evidence of a far more humid climate than those found in the older Barun Goyot and Djadochta Formations. However, caliche deposits indicate at least periodic droughts. Sediment was deposited in the channels and floodplains of large rivers. Fossils found in these sediments also indicate a rich ecosystem, offering diverse food in abundant amounts that could sustain massive dinosaurs like Deinocheirus.
The habitats in and around the Nemegt rivers where Deinocheirus lived provided a home for a wide array of living things. Occasional mollusc fossils are found, as well as a variety of other aquatic animals like fish and turtles. Nemegt crocodylomorphs included several species of Shamosuchus, a genus with teeth adapted for crushing shells. Mammal fossils are extremely rare in the Nemegt Formation, but many birds have been found, including the enantiornithine Gurilynia and the hesperornithiform Judinornis, as well as Teviornis, a possible early member of the Anseriformes, the bird order that includes ducks and geese. Herbivorous dinosaurs of the Nemegt Formation include ankylosaurids such as Tarchia, and the pachycephalosaurian Prenocephale, large hadrosaurids such as Saurolophus and Barsboldia, and sauropods such as Nemegtosaurus, and Opisthocoelicaudia. Predatory theropods included Tarbosaurus, the small tyrannosaurid Alioramus, troodontids (Borogovia, Tochisaurus, and Saurornithoides), oviraptorosaurians (Elmisaurus, Nemegtomaia, and Rinchenia), and Bagaraatan, sometimes considered a basal tyrannosauroid. Other theropods, like the gigantic Therizinosaurus and ornithomimosaurians such as Anserimimus and Gallimimus from the Nemegt Formation, may have been primarily herbivorous.
History of discovery
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. The coordinates for the find were . 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. The specimen has been since re-catalogued as MPC-D 100/18.
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." 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 the early 2010s, informal reports of new specimens of Deinocheirus surfaced, describing the animal as a gigantic ornithomimosaur with a hump on its back and a skull that resembled a cross between an ornithomimosaur and a hadrosaur. In 2013 these reports were clarified as the findings were presented before the Society of Vertebrate Paleontology. The new specimens are housed in the Paleontological Center of Mongolian Academy of Sciences, were given the specimens numbers MPC-D 100/127 and MPC-D 100/128.
MPC-D 100/128 was first discovered in 2006, during the Korea-Mongolia International Dinosaur Expedition. It was found in the Altan Uul IV locality of the Nemegt Formation, at the specific coordinates fossil poachers, who damaged the specimen but did not remove anything as they could not find the head, hands or feet, common elements poached that could sell for large sums of money. The second specimen, found in 2009 expeditions by palaeontologists, was given the number MPC-D 100/127. It was from the Bugiin Tsav locality at the coordinates . This specimen included many partially articulated bones and multiple blocks. It too had been damaged by poachers, who found and removed the skull, hands and feet. However, they were apparently rushed as they left behind a single toe bone.. The first people to uncover it were
They were in 2011 obtained by the French fossil trader François Escuillé who donated them to the Royal Belgian Institute of Natural Sciences. He and Pascal Godefroit informed the other authors of the presence of a skull, left hand and feet in a private collection in Europe. The specimens were bought by the authors, who guaranteed that it was their specimen because the single toe bone fit perfectly into the unprepared matrix of the poached feet. In May of 2014 the fossils were finally repatriated to Mongolia. Together, both specimens provide almost the entire skeleton of Deinocheirus, as MPC-D 100/127 includes all material apart from the middle dorsal vertebrae, most caudals, and the right forelimb; MPC-D 100/128 fills in most gaps of the other skeleton, with nearly all post-cervical (dorsal and caudal) vertebrae, ilia, partial ischia, and most of the left hindlimb. The specimens were described in a letter to Nature Magazine in 2014 by Yuong-Nam Lee, Rinchen Barsbold, Philip J. Currie, Yoshitsugu Kobayashi, Hang-Jae Lee, Pascal Godefroit, François Escuillié & Tsogtbaatar Chinzorig.
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