Deinocheirus

DeinocheirusTerrible Hand
Classification
Domain	Eukaryota
Kingdom	Animalia
Phylum	Chordata
Subphylum	Vertebrata
Superclass	Tetrapoda
Clade	Sauropsida
Class	Reptilia
Clade	Archosauria Avemetatarsalia Ornithodira Dinosauria Saurischia Theropoda Neotheropoda Averostra Tetanurae Orionides Avetheropoda Coelurosauria Maniraptoriformes Ornithomimosauria
Superfamily	Ornithomimoidea
Family	Deinocheiridae
Species	Deinocheirus mirificus
Presence
Location	Nemegt Formation, Ömnögovi Province, northwest Gobi Desert, south Mongolia
Temporal Range	70 million years ago, Maastrichtian Stage, Late Cretaceous Period
Episodes	Freshwater (Segment 3)
Characteristics
Height	4.4 - 5.8 meters (14 - 19 feet)
Length	11 - 12 meters (36 - 40 feet)
Mass	6.36 - 7.3 metric tons (7 - 8 short tons)
Diet	Omnivorous
Skull Length of 1 meter (3 feet, 4 inches) Sclerotic Ring Outer Diameter of 8.4 centimeters (3.31 inches), indicating a diurnal lifestyle Arm Length of 2.4 meters (8 feet) Hand Length of 77 centimeters (2 feet, 6 inches) Hand Claw Length of 20 centimeters (8 inches) Relies on gastrolith stones to mash up food

Deinocheirus (Terrible Hand) is a genus of ornithomimosaurian theropod dinosaur that lived in the Nemegt Formation of the Ömnögovi Province, an area in the northwest region of the Gobi Desert in southern Mongolia, 70 million years ago, during the Maastrichtian stage of the Late Cretaceous Period. Named for massive, 2.4-meter (8-foot) front limbs discovered in 1965 (one of the longest forearms among bipedal dinosaurs), Deinocheirus remained an enigma for 49 years until its unusual nature was finally made clearer when two more complete specimens were described in 2014.

Paleobiology

Size and Physique

Male Deinocheirus concept art by Gaëlle Seguillon

“ Deinocheirus. It's even taller than T. rex, and its massive duck-billed snout is very effective in gathering water plants. ”

― David Attenborough, Freshwater

Deinocheirus is a massive theropod, estimated in 2016 to be around 11 - 12 meters (36 - 40 feet) in length. Given its default, hunched posture (as is depicted on the show), it was approximately 4.4 meters (14 feet) in height, making it a foot taller than T. rex. However, assuming that it had a more upright stance, it can reach a height of around 5.8 meters (19 feet) tall, making it around 10.2 centimeters (4 inches) taller than the contemporary Therizinosaurus, unless the latter reared up as tall as it can, past its default posture, thus reaching up to around 7.4 meters (24 feet) in height. Aside from Therizinosaurus (assuming that Deinocheirus did not have a more upright normal posture), the only other theropod that surpasses Deinocheirus in terms of default height is Gigantoraptor, an oviraptorosaur that lived in Mongolia 96 million years ago, which can grow up to 6.5 meters (21 feet, 4 inches) tall.

“ With its feathered body and duck bill, the eight-ton Deinocheirus wades through an Asian wetland in search of relief from pesky biting flies. ”

― The official Apple TV+ episode synopsis for Freshwater

As with most bulky animals, Deinocheirus has many hollow bones, some highly-pneumatized by invading air sacs, to help it save weight, though it was still very heavy, weighing around 6.36 - 7.3 metric tons (7 - 8 short tons), its mass supported by an enlarged pelvis with strong muscular attachments and two relatively short legs with blunt, broad claws that were more like those of ornithischians rather than the tapered claws of other theropods. It is the largest ornithomimosaur ever discovered, having traded the sleek, ostrich-like body plan and speed of relatives like Ornithomimus for a slower but more massive form, and, along with its contemporary, the equally bizarre Therizinosaurus, as well as Gigantoraptor (which lived in Mongolia almost 30 million years prior to both Deinocheirus and Therizinosaurus), it is one of the largest maniraptoriforms, with all three of them having the longest necks of any theropod dinosaur.

Despite its great bulk, the dorsal ribs of Deinocheirus were tall and relatively straight, indicating that its body was narrow. Deinocheirus is also known for the tall neural spines on its 12 back vertebrae linked by interconnecting ligaments, forming a tall sail from the lower back to the base of the tail, similar to that of Spinosaurus. The pneumaticity of these dorsal spines are comparable to those of sauropods.

Brain and Senses

Deinocheirus has a large and globular brain like those of troodontids and avian dinosaurs (birds), with an expanded cerebrum as is expected for theropods. However, in proportion to the skull, the brain is small and compact, giving Deinocheirus an estimated reptile encephalization quotient of 0.69, more like that of a sauropod than that of a theropod (by comparison, the encephalization quotient estimate for T. rex around that time was 5.44 - 7.63), though caution should be taken when it comes to accepting these values, as encephalization quotients for extinct animals are not entirely reliable. Whatever the case, it is clear that, having grown large (possibly to better defend itself against large predators like Tarbosaurus), not only did Deinocheirus lose the speed and agility seen in smaller ornithomimosaurs (especially since its femora, thigh bones, are longer than its tibiae, lower leg long bones), it also lost the large brain-to-body proportion, and thus likely also had reduced balance and coordination. The proportionally-small brain of Deinocheirus is also believed to reflect its omnivorous diet and social capabilities, hence, Prehistoric Planet depicts the lone male Deinocheirus as solitary. Despite its low intelligence, Deinocheirus is still capable of simple problem solving, able to recognize parts of the environment he can use to his advantage; when his long arms (2.4 meters or 8 feet in length) and blunt claws (20 centimeters or 8 inches in length) proved unable to reach and scratch every part of his body, he rubbed himself on a dead tree to get to places his arms cannot reach.

As indicated by the size of its sclerotic rings, which have an outside diameter of 8.4 centimeters (3.31 inches), Deinocheirus has small eyes in proportion to its head, indicating that it is diurnal, primarily active during the day.

Feathers

See more: Thermoregulation

See more: Thermoregulation

Prehistoric Planet depicts Deinocheirus with a thick coat of greenish-brown feathers, matching its swampy habitat. While pennaceous feathers are known in smaller ornithomimosaurs, the extent of feathers on Deinocheirus is not fully clear. According to Dr. Darren Naish, lead consultant of Prehistoric Planet, the environment Deinocheirus lived in is understood to be cool, and dinosaurs may have been better at temperature control compared to big mammals, thus serving as somewhat of a justification for the thick coat of feathers on Deinocheirus. The presence of at least two fused vertebrae by the end of its tail indicates that Deinocheirus at least sported a pygostyle, a fan of tail feathers, like oviraptorosaurs and therizinosaurs. On Prehistoric Planet, Deinocheirus has blue feathers flaring out from the tip of its tail, faintly resembling the more complex pygostyle of Dromaeosaurus.

Bill

Deinocheirus scooping up plants with his broad, toothless bill

The only known Deinocheirus skull, belonging to MPC-D 100/127 (the largest discovered specimen so far), is more than a meter (3 feet, 4 inches) in length, with a jaw depth that scales more like that of a tyrannosaur's skull rather than those of other ornithomimosaurs, and a wide duck-like bill similar to those of hadrosaurs. Unlike hadrosaurs, however, which possess dental batteries (hundreds of teeth, stacked in rows to form a grinding surface), Deinocheirus has a toothless bill, with a low, slender upper jaw and a massive, deep lower jaw, implying the presence of a massive tongue. Additionally, the attachment points for the muscles responsible for jaw movement are small, indicating that the long, toothless skull of Deinocheirus had a weak bite force. Because its jaws are only capable of vertical movement, it cannot chew, so it instead relied on its large, muscular tongue to help suck in and force food to the back of its mouth, and compensated for the lack of chewing ability by relying on gastrolith stones in its gut to mash up food. The show depicts Deinocheirus with a yellow bill and a ring of bare, blue skin within the facial area past the bill.

Limbs

Deinocheirus about to pull plants from the bottom of the river with his claws

“ Water plants are rich in nutrients, and his huge, curved claws, eight inches long, enable him to dredge them up from deep beneath the surface. ”

― David Attenborough, Freshwater

Along with Therizinosaurus, the robust arms of Deinocheirus were among the largest of any bipedal dinosaur, reaching 2.4 meters (8 feet) in length, with large, blunt, 20-centimeter (8-inch) claws on its three-fingered hands, earning it the name "Terrible Hand". While the show depicts these arms as tools to help gather plants, they may have also served many other plausible purposes, from thwacking fish (which are proven to also be part of the animal's diet) to intimidating or even striking rivals and predators.

Compared to most theropod dinosaurs, the toe claws of Deinocheirus were unique due to being short, blunt, and broad rather than tapered into narrow points. This helped prevent its large feet from sinking in wet substrates like mud and sand by spreading its weight, further supporting the idea that Deinocheirus waded in the rivers of the Nemegt Formation. A 2018 study reported the presence of three-toed tracks in the Nemegt Formation alongside sauropod footprints, first discovered in a 2007 expedition. While initially believed to be those of hadrosaur feet, there is a noticeable lack of associated hadrosaur hand tracks. Because the feet of Deinocheirus are known to resemble those of hadrosaurs, there is a possibility that these are actually the footprints left behind the giant ornithomimosaur.

Paleoecology

Paleoenvironment

Main: Nemegt Formation

Main: Nemegt Formation

The plains of the Nemegt Formation, flooded by overflowing rivers

“ In parts of Central Asia, heavy seasonal rains fill the rivers until eventually, they overflow their banks. The surrounding plains are flooded. ”

― David Attenborough, Freshwater

The Ömnögovi is the largest aimag (province) of Mongolia, found in the south of the country, in the northeast portion of the Gobi Desert. Within this aimag is an area called the Nemegt Basin, known locally as the "Valley of Dragons" due to its rich fossil content. It encompasses three formations showing the states the area underwent throughout the Late Cretaceous, namely, the Djadochta (75 - 71 million years old), Barun Goyot (72 - 71 million years old), and Nemegt (70 million years old) Formations. Deinocheirus lived in the last of the three formations, which showed evidence of a rich, humid environment with large, braided and meandering river channels, tidal flats, and forests, providing an overall swampy environment where bodies of water could overflow due to heavy rains. Deinocheirus is perfectly adapted to living in such environments, with large, powerful arms that could dredge up water plants from the bottom of the river, and short yet broad, blunt foot claws that helped prevent its feet from sinking too deeply into the river bed.

Paleofauna

Deinocheirus would have coexisted with similarly-large creatures like Barsboldia, Nemegtosaurus, Opisthocoelicaudia, and other, larger titanosaurs that may potentially rival Argentinosaurus in size. It also shared its habitat with smaller animals like Tarchia, Mononykus, Prenocephale, troodontids, and velociraptorine dromaeosaurids. Due to its great height, Deinocheirus would have been able to feed from relatively higher trees than some herbivores, and it would have been an intimidating sight to behold, being among the tallest and heaviest non-sauropod dinosaurs in the area alongside Therizinosaurus. Even a large Tarbosaurus (the apex predator of the region) would not have been able to bite any higher than the belly or thigh of an adult Deinocheirus or Therizinosaurus, and, though it has a tremendous, bone-crushing bite force, trying to do so would put the tyrannosaur within the striking range of the long, powerful clawed forearms of both animals. Even so, Deinocheirus is not completely immune to predation, as proven by Tarbosaurus bite marks on a Deinocheirus gastralia (ventral bone found between the sternum and pelvis), either due to scavenging or hunting.

Feeding Preferences

“ This male feeds voraciously, having eaten very little during the long, dry season. ”

― David Attenborough, Freshwater

Deinocheirus is said to have not eaten much during the dry season, hence, when the wet season begins, he wades through a swampy environment formed by a river that overflowed its banks, voraciously scooping up vegetation from the riverbed with his massive duck bill and huge arms, tipped with claws 20 centimeters (8 inches) in length. While Deinocheirus is depicted as living on a diet that consists almost entirely of wet vegetation, evidence of fish vertebrae and scales in one specimen's stomach indicates a degree of omnivory. Also found in its stomach are more than 1,400 gastroliths, stones around 8 - 87 millimeters (0.31 - 3.43 inches) in size, taking up around 0.22% of its total body mass, indicating that it processed food in its gut rather than its toothless jaws, which were only capable of simple vertical actions and thus cannot chew. Overall, Deinocheirus appears to have a water-based diet like ducks, capable of foraging for plants and fish from bodies of water as well as engaging in non-selective browsing on land like some sauropods and hadrosaurs.

Appearance

	Freshwater, Segment III
	Setting Nemegt Formation, Gobi Desert, Mongolia

Freshwater, Segment III

Setting
Nemegt Formation, Gobi Desert, Mongolia

Deinocheirus approaches a tree to scratch himself

In the third segment of Freshwater, one male Deinocheirus is seen feasting on plants at the bottom of a swollen river, having eaten very little during the long, dry season. Unfortunately, he is pestered by flies, which prove to be irritating and even painful.

“ He himself is a source of food for smaller creatures. Bloodsucking flies, which infest his coat. They're irritating, and even painful, and while his huge claws enable him to have a good scratch, there are always some spots that are just out of reach. To get to them, he needs assistance... a dead tree. That could be the answer. ”

― David Attenborough, Freshwater

The Deinocheirus attempts to scratch himself with his long arms, but is unable to reach some parts of his body. Spotting a dead tree, Deinocheirus heads for it and slams himself upon the tree (scaring off an enantiornithine bird perched on one of the branches in the process), rubbing his back and head on it to get rid of the itching sensations.

“ And now, he can get back to feeding. But a diet that consists almost entirely of wet vegetation does have one, inevitable consequence. What was food for one becomes fertilizer for many others, and a giant as big as Deinocheirus can produce over 20 tonnes of dung every year. ”

― David Attenborough, Freshwater

After having fully scratched himself, the Deinocheirus returns to feeding on plants, defecating on the spot, his excrement sinking to the bottom of the swamp, serving as fertilizer for the very plants he feeds on. Swishing his tail in the water to get rid of the fecal matter still on him, the Deinocheirus wanders off.

References

General

Dr. Darren Naish

Prehistoric Planet