When I was a young boy who was madly into palaeontology and had significantly less adult responsibilities, I remember walking through the ever popular dinosaur exhibition in the Natural History Museum in London. Among the many displays, which ranged from models of dinosaur nests to the big skeleton of the Triceratops, there was one that always stood out to me. It was a pair of huge arms, complete with hands tipped with large claws. Unlike the proportionately tiny arms of Tyrannosaurus Rex, (I say proportionately as T-Rex arms were still as long as a humans) or the backwards facing stump like arms of Carnotaurus these arms were long with highly developed “hands”, displayed in such a way that it seemed like they could either give you a large hug or grab you and carry you away into the night. These arms, discovered in 1965, belonged to a dinosaur known as Deinocheirus mirificus; meaning “terrible hand which is unusual”. Quite a fitting description for a giant pair of arms! This beast lived in Mongolia 70 million years ago during the Late Cretaceous. At the time I first saw this fossil palaeontologists still didn’t really know what kind of dinosaur it was as no other fossils had been found except for the arms. It was a tricky task, how can you build up the image of an animal from just its arms. Imagine trying to construct what a human looked like, how we behaved, what we ate and what our social lives were like from just our arms. From this incredible looking fossil palaeontologists were able to deduce that it was a species of theropod dinosaur, but apart from that it was only guesswork.
That is, until new fossilised material was discovered in 2009 by a team from South Korea’s Institute of Geoscience and Mineral Resources in Kigam, lead by a palaeontologist named Yuong-Nam Lee. These were not only more giant arms, but also two nearly complete skeletons that finally solved the almost 50 year mystery.
It was much weirder than anything my younger self could have imagined. For starters, it was not a vicious giant carnivore like other large theropods such as Giganotosaurus. Instead it was an omnivore, using its duck-like beak to eat vegetation with a helping of small fish on the side. Deinocheirus was a slow, lumbering giant stretching to eleven metres in length, and weighing up to 6 tonnes. To add to the weirdness, it also possessed back spines that may have formed part of a hump like structure on its back, and it may also have even been covered in feathers. The end of its tail bones were fused together into a pygostyle. This same structure is seen today in modern birds and is used to support long tail feathers, so it’s possible that Deinocheirus also had a feathery tail fan! The large arms were probably used to gather out of reach plants closer to its mouth, rather like a giant panda grabbing bamboo, or as a defence against predators, such as the tyrannosaurid Tarbosaurus whose bite marks are seen on the bones. The fossils did confirm that it was a theropod dinosaur and part of the ornithomimids, a group of dinosaurs which also included Gallimimus of Late Cretaceous North America. However Deinocheirus is very bizarre even when compared to other ornithomimids. Other species were smaller, with slender bodies and legs built for speed (not too dissimilar in lifestyle to the modern day Ostrich).
So as it turns out, Deinocheirus is not the terrifying monster that I thought it was when I saw those fossil arms all those years ago. Instead, in looks and lifestyle, it seems like the result of a group of mad scientists genetically splicing a T-Rex, a duck and an ostrich together to see what they get. However this new depiction, in my view, is just as fascinating and awe inspiring, and shows how diverse dinosaurs really were.
Lee, Y., Barsbold, R., Currie, P. et al. Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus. Nature 515, 257–260 (2014). https://doi.org/10.1038/nature13874
Yong, Ed “Deinocheirus Exposed: Meet The Body Behind the Terrible Hand”, National Geographic, Oct. 22, 2014, nationalgeographic.com/science/phenomena/2014/10/22/deinocheirus-exposed-meet-the-body-behind-the-terrible-hand/
Hecht, Jeff. “Stolen dinosaur head reveals weird hybrid species” NewScientist, May. 12, 2014, newscientist.com/article/dn25551-stolen-dinosaur-head-reveals-weird-hybrid-species/