Deinocheirus mirificus was an ornithomimosaur that roamed the Earth during the Late Cretaceous epoch, approximately 70 million years ago. Its name, meaning “horrible hand,” refers to its remarkably large forelimbs. This dinosaur lived specifically within the Maastrichtian stage of this geological period.
The Late Cretaceous World
The Late Cretaceous period, spanning from about 100.5 to 66 million years ago, featured a global climate significantly warmer than the present day. While a cooling trend became evident towards its end, the absence of polar ice caps and higher sea levels characterized much of this epoch. Large inland seas were common, and continental landmasses continued their slow drift, shaping distinct regional environments.
Within this global context, the region now known as the Gobi Desert in Mongolia, where Deinocheirus fossils were found, was a humid landscape. It consisted of extensive floodplains, crisscrossed by numerous river channels, and dotted with shallow lakes and swamps. This wet environment supported a rich variety of plant life, including dominant flowering plants (angiosperms), alongside conifers, ferns, and cycads.
This period marked the end of non-avian dinosaurs, which populated diverse ecological niches. Large predatory tyrannosaurids like Tarbosaurus, various hadrosaurs, ceratopsians, and other theropods such as Therizinosaurus shared these expansive habitats. The abundant flora and diverse fauna created a complex ecosystem.
Unearthing Deinocheirus’s Timeline
The initial discovery of Deinocheirus occurred in 1965 when Polish paleontologist Zofia Kielan-Jaworowska unearthed nearly 8-foot-long forelimbs and shoulder girdles in the Nemegt Formation of Mongolia. For decades, these partial remains were the primary evidence of its existence, leaving much about its appearance and lifestyle unknown.
Breakthroughs came in the early 2000s with the discovery of more complete specimens, including skulls, formally described in 2014. These later finds, some of which had been illegally collected and subsequently repatriated to Mongolia, provided crucial insights into the dinosaur’s anatomy.
Determining the precise age of these fossils relies on geological methods, particularly by studying the rock layers of the Nemegt Formation. While the Nemegt Formation itself has not been directly dated using radiometric methods due to the absence of suitable volcanic rocks, its age is established through biostratigraphy. This technique involves comparing the fossil assemblage within the Nemegt Formation to other well-dated fossil sites around the world.
The presence of other known dinosaurs like Tarbosaurus and Therizinosaurus helps to pinpoint the Nemegt Formation’s age. Based on these correlations, scientists have determined that Deinocheirus lived during the early Maastrichtian stage of the Late Cretaceous, approximately 70 to 71 million years ago.
Deinocheirus and Its Ancient Ecosystem
Deinocheirus was a large dinosaur, reaching lengths of up to 11 meters and weighing around 6.3 to 7 tons. Despite its bulk, it possessed hollow bones. Its most distinctive features included a tall, sail-like hump along its back formed by elongated neural spines, and a long, duck-billed snout.
The skull shape, characterized by a weak bite force and a likely large tongue, suggests an omnivorous diet. Evidence such as gastroliths (stomach stones) indicates it consumed plant material, while the discovery of fish scales and vertebrae alongside some specimens points to a diet that included fish. Its long, clawed forelimbs may have been used to pull down branches for browsing or to dig for aquatic vegetation.
Within its humid, riverine environment, Deinocheirus occupied an ecological niche. It coexisted with predators like Tarbosaurus, with some Deinocheirus bones showing bite marks attributed to this large tyrannosaur. The dinosaur likely competed for plant resources with other large herbivores, including sauropods and the long-clawed Therizinosaurus.