Many discoveries in paleontology are not complete specimens . Thanks to comparative anatomy , we can identify which family they belong to and even if they are a new species. But many of those incomplete fossils remain that way to this day. Other times, luckily, new fossils end up appearing that allow the missing pieces to be completed. Among invertebrates, such a case was Anomalocaris , a Middle Cambrian creature related to arthropods. And among vertebrates, the case of the Deinocheirus dinosaur is very noteworthy.
For the beginning of this story we must go to the Gobi Desert, and go back in time to the Polish-Mongolian expeditions that took place from 1960, and which were led by the Polish paleontologist Zofia Kielan-Jaworowska . In the 1965 expedition, Zofia found the first specimen of an enigmatic dinosaur in the Cretaceous sediments of the Nemegt Formation: a pair of arms , with their scapulae or shoulder blades, and a few scattered bones. These mysterious arms, by comparison of their anatomy with other dinosaurs, must have been from a theropod dinosaur – a group to which carnivorous dinosaurs belong. But the surprising thing was that those arms were almost eight feet long.
In 1970, paleontologists Halszka Osmolska and Ewa Roniewicz published the holotype specimen (original specimen on the basis of which a new species is described), which included both forelimbs (excluding the claws of the right hand), the entire shoulder girdle, and a few vertebrae and ribs. They named it Deinocheirus mirificus (meaning terrible and peculiar hand). But the fact that its remains were so fragmentary prevented knowing more details about this animal, nor its correct classification within theropod dinosaurs, nor its anatomy and appearance, for almost half a century.
The scientific literature often described it as one of the most “enigmatic” dinosaurs and over the decades various hypotheses were considered. Osmólska and Roniewicz in their original description considered that it did not belong to any known family of theropods, although they pointed out its resemblance to ornithomimosaurs , a group of graceful and medium-sized dinosaurs, closely related to birds, to which Gallimimus belongs, for example. It was the paleontologist John Ostrom who first formally proposed that Deinocheirus belong to the Ornithomimosauria group.
This is how for a long time, in books on paleontology and dinosaurs, a silhouette of an ornithomimosaur scaled to the size of its arms was depicted, something that was impressive and, why not say it, chilling. And that’s how we got to 2013.
Like every year, the Society of Vertebrate Paleontology (SVP) was preparing to hold its annual meeting, in which paleontologists presented their research news. And by the time the official program of talks was published, the news spread through the paleontological community: after 50 years, new Deinocheirus specimens had been found and its mystery was closer than ever to being solved. Paleontologists Lee, Barsbold, Currie and their collaborators announced the discovery of two new specimens during that conference.
After finding the bones that were missing from one of these specimens – they had been looted and sold – the skeleton was completed and deposited in the Central Museum of Mongolian Dinosaurs in Ulaanbaatar. And finally, in 2014 the discovery was published. Between the classical material from the Polish-Mongolian expeditions and the recovered skeleton eggs, the entire skeleton of Deinocheirus could be reconstructed half a century later.
This is how we found out that Deinocheirus was one of the strangest dinosaurs that ever lived . It is the largest ornithomimosaur discovered to date: it measures between 11 and 12 meters long, it weighs between 6 and 7 tons and the hip was about 4 meters high. For an ornithomimosaur, it was extremely bulky and robust, although like most theropods it had many pneumatized bones . Its arms were more than two meters long and its hands were equipped with sharp claws. Its legs were short in proportion to the rest of its body and the spines of its thoracic vertebrae were high, forming a kind of sail or hump. Its tail ended in the form of a pygostyle : a fusion of vertebrae that is observed in birds and usually serves to carry the tail feathers, suggesting the presence of a fan of feathers. Its skull was a meter long, and its beak was wide and reminiscent of hadrosaurs – the duck-billed dinosaurs.
After decades of excavations, research and discoveries, this dinosaur went from being considered one of the greatest enigmas of paleontology to possibly becoming the strangest dinosaur found to date. The fossil record never ceases to amaze us, and this is further proof. So that later there are those who believe that everything is already discovered…
References:
Kielan-Jaworowska, Z.; Dovchin, N. 1968. Narrative of the Polish-Mongolian Palaeontological Expeditions 1963–1965. Palaeontologica Polonica, 19: 24.
Osmólska, H.; Roniewicz, E. 1970. Deinocheiridae, a new family of theropod dinosaurs. Palaeontologica Polonica, (21): 5-19.
Lee, YN et al. 2014. Resolving the long-standing riddles of a giant ornithomimosaur Deinocheirus adventure. Nature, 515 (7526): 257-260.
Sanz, J. L. 2007. Dragon Slayers: A Story of the Paleontologists Who Discovered and Studied the Dinosaurs . Ed. Ariel.
Gascó, F. 2021. That was not in my dinosaur history book . Guadalmazán.
