First Described By: Osmólska & Roniewicz, 1970
Classification: Dinosauromorpha, Dinosauriformes, Dracohors, Dinosauria, Saurischia, Eusaurischia, Theropoda, Neotheropoda, Averostra, Tetanurae, Orionides, Avetheropoda, Coelurosauria, Tyrannoraptora, Maniraptoromorpha, Maniraptoriformes, Ornithomimosauria, Ornithomimoidea, Deinocheiridae
Time and Place: 70 million years ago, in the Maastrichtian of the Late Cretaceous
Deinocheirus is known from the Nemegt Formation of Ömnögovi, Mongolia
Physical Description: Deinocheirus is one of the absolute weirdest, fantastical, most surprising discoveries of the 2010s in paleontology, and the answer to a mystery older than most of the readers of this blog. Deinocheirus was originally known from two very long, distinctive arms - arms so long, that they could very easily engulf a person. In fact, many of the photographs of the fossil are of an individual standing in between the hands, in order to give scale to them. But these arms and hands gave very little in the way of information about what Deinocheirus looked like. Eventually, it was determined that Deinocheirus was an Ornithomimosaur - but the scale of the arms indicated it would be a ridiculously huge Ornithomimosaur.
By Slate Weasel, in the Public Domain
And then, luckily, more fossils were found of it. To be sure, it was a ridiculously large Ornithomimosaur - in fact, given the fact that it was an Ornithomimosaur, a group of distinctively feathered dinosaurs, it is almost certainly one of the largest feathered animals known to date - but it was More than that by a large margin. It was probably around 11 meters long, weighing up to 6.4 tonnes. It had some of the largest forelimbs known of any bipedal dinosaur - only rivaled by Therizinosaurs - and the arms in question are 2.4 meters long. Its skull, only one specimen of it having been found, is honestly weirdly duck-shaped. It was low and narrow, like other Ornithomimosaurs, but with a longer snout than its relatives. This snout was wide and shaped like a spatula - similar to the snouts of duck-billed dinosaurs and ducks alike. There weren’t any teeth in the jaws, which ended in a distinctive beak, and it was turned down, to make it look fairly massive and deep. When you get down to it, Deinocheirus had a ridiculously triangular head.
As for the rest of the body, Deinocheirus had very long and narrow shoulder blades, connected to very pronounced and triangular shoulders. Weirdly enough, compared to the shoulders, Deinocheirus actually had smaller arms than its close relative Ornithomimus - ie, it had a smaller shoulder to arm ratio than its relatives. It had a U-shaped wishbone, which is fascinating since we don’t have the wishbone of other Ornithomimosaurs. Unlike other Ornithomimosaurs, it didn’t have pinched toe bones, so it wasn’t highly adapted for fast movement; it also had very blunt and broad foot claws like those of large Ornithischian dinosaurs. It may have been a bulky animal, but it was also quite narrow - with very tall, straight ribs. It had an S-curved neck, especially given the shape of the skull, which extended back into the oddly indeed shaped back. The spines on the back of Deinocheirus got progressively and progressively longer, until reaching lengths similar to those found on Spinosaurus - indicating that Deinocheirus had a sail or a hump, much like Spinosaurus did. There were interconnecting ligaments on the spines, strengthening it. That sail then lessened as it went down along the tail, until the tail had a very skinny appearance compared to the rest of the body. It had extremely lightweight air bones, through which the respiratory system ran. This also allowed it to be even more lightly built, which aided it in its large size. Interestingly enough, the tail ended in fused vertebrae, like those in Therizinosaurs, Oviraptors, and Birds - indicating it had a pygostyle!
By Michael B. H., CC BY-SA 3.0
As for feathers, it would have probably been covered in a layer of fluff all over the body. Fancy, pennaceous feathers would have been present on the arms and the end of the tail - in fact, a tail fan would have been attached to that pygostyle and used in display. It may have also had display feathers on the back of the head or even the legs. However, that being said, its large size may indicate a decrease in fluff so that it could stay cool - while it is still most likely that it had distinctive and extensive feathers as in its close relatives, fossil evidence is needed to determine its exact integument situation.
Diet: Deinocheirus was, distinctively, a large herbivore - specializing on water plants and other soft greens that could be shoveled up with that spoon beak.
By Meig Dickson & Diane Remic
Behavior: Deinocheirus probably spent a good amount of time foraging at or near the water, gathering up water vegetation with its spatulate bill. It also utilized gastroliths - stones that were swallowed to grind up that wet and mushy vegetation in the stomach. This was important and helpful, since it couldn’t do much grinding without teeth in its mouth. It did have a very long and large tongue, which allowed it to pull up extensive amounts of plant material up from the ground. It would use the blunt and short claws of its hands in order to dig up plants from the water - and to decrease resistance as it sucked them up from the swamps.
Deinocheirus wasn’t a fast animal - the short and stocky legs meant that it moved slowly through its environment, and used its large size to protect itself against predators instead. It grew extremely rapidly, too, reaching large size before sexual maturity. Sadly, its giant size means that it didn’t have a very large brain compared to its body size - in fact, the ratio in question was more similar to that of sauropods than other theropods. That beings aid, it was similar in shape to birds and troodontids and other birdie theropods, indicating that it still had a decent sense of smell - which is fascinating as it had a good respiratory system as well. As a warm-blooded animal, however, it would have been very active; and as a dinosaur, it probably took care of its young in nests. It is uncertain whether or not it would have lived in social groups, but it certainly wouldn’t have been particularly isolated as an herbivore.
Ecosystem: The Nemegt Formation was a wetland, filled with a wide variety of dinosaurs right before the end of the time of non-avian dinosaurs. The area was filled with large river channels, which created extensive shallow lakes, mudflats, and floodplains - like the modern Okavango Delta in Botswana. There were also thick coniferous forests surrounding the ecosystem, allowing for drier areas to be retreated to in addition to the swampy mess that was the bulk of the environment. Here, many plant-eaters specialized in feeding on water plants - in fact, I often joke that the Nemegt is the Land of Ducks. In addition to Deinocheirus, there were two other Ornithomimosaurs - Gallimimus and Anserimimus - both featuring duck-like beaks for feeding on water plants. Other ducks of the region include Saurolophus, which, as a duck-billed dinosaur, was especially adapted for feeding on soft plant material; and Teviornis, an early ACTUAL duck relative with the appropriate bill.
This place also had other dinosaurs that weren’t ducks, of course. There was the large tyrannosaur, Tarbosaurus, which is known to have directly preyed upon Deinocheirus. There were troodontids too, like Tochisaurus, Zanabazar and Borogovia, which would have preyed upon the eggs and young of Gallimimus. There were a million different Oviraptorosaurs, making this also the ecosystem of the Chickenparrots - Avimimus, Elmisaurus, Conchoraptor, Nemegtomaia, Nomingia, and Rinchenia, were all present and feeding on the drier vegetation of the area. There was also the Hesperornithine Brodavis, one of the few freshwater species of Hesperornithines. There were other herbivores too, of course - Pachycephalosaurs like Homalocephale and Prenocephale, ankylosaurs such as Tarchia and Saichania, the titanosaur Nemegtosaurus, and the Therizinosaur Therizinosaurus - which probably all stuck to drier areas of the ecosystem than Deinocheirus. Tarbosaurus wasn’t the only Tyrannosaur, either - there was the smaller Alioramus which would have been more of a nuisance for baby Deinocheirus than the adults. And for other predators, there was the raptor Adasaurus, which may or may not have been a direct descendant of Velociraptor. As for non-dinosaurs, there was at least one Azdarchid, the small mammal Buginbaatar, and a variety of crocodilians that would have been non-negligible threats to young Deinocheirus. There were also plenty of turtles, which would have been a very noticeable part of the wider ecosystem.
Other: Deinocheirus is such a weird Ornithomimosaur, it gave its name to an entire group of them - these guys were slower than the Ornithomimids, and larger, but still had that general Ostrich-mimic shape. Instead of being lean and fast, they were large and slow. The discovery of the specimens of Deinocheirus that allowed us to actually learn what it looked like was a big one - since, prior to that point, Deinocheirus had been one of the most fascinating mysteries of dinosaur science, as all we had were two giant hands! Because of its large size, duck-like appearance, and above all, nightmare fodder in terms of past legend and current appearance, Deinocheirus has been fondly dubbed as Duck Satan for a makeshift common name.
