The discovery of Deinocheirus mirificus, the “terrible hand,” began in 1965 with the unearthing of two colossal, 8-foot-long forelimbs in Mongolia’s Gobi Desert. For nearly five decades, this massive arm was the only evidence, leading to speculation that it was an enormous, predatory beast, perhaps a relative of dinosaurs like Allosaurus. However, the discovery of more complete skeletons in the 2000s revealed a creature far stranger than imagined, establishing it as an unusually large ornithomimosaur. This new evidence resolved the mystery about the animal’s lifestyle, body shape, and, most importantly, its diet.
Physical Adaptations for Feeding
The head and neck anatomy of Deinocheirus provide the first clues regarding its specialized feeding strategy. Unlike its smaller ornithomimosaur cousins, Deinocheirus possessed a massive, 3.3-foot-long, toothless skull. The jaws terminated in a broad, flattened beak, shaped similar to that of a duck. Evidence of weak jaw musculature indicates the dinosaur had a weak bite force, unsuitable for tearing meat or crushing tough plant material.
The long, S-curved neck allowed the head to reach low-lying vegetation or forage near the ground. Its massive body was supported by tall neural spines over the back, forming a prominent sail or hump. Short, heavy legs and broad-tipped feet suggest a slow-moving animal adapted for wading in soft, muddy ground near water sources. The enormous forelimbs, which gave the dinosaur its name, ended in large, blunt claws suited for digging up plants or gathering food from the substrate rather than seizing prey.
Internal and Chemical Evidence
Direct evidence from fossilized gut contents cemented the picture suggested by the anatomy. Within the rib cage of one specimen, paleontologists discovered more than 1,400 gastroliths, or stomach stones. These stones served as a “gizzard” for the toothless dinosaur, grinding down tough plant fibers to aid in digestion, a characteristic seen in many modern herbivorous birds. The large number of grinding stones strongly suggests a reliance on high volumes of vegetation.
Intermingled with these gastroliths were the remains of small animals, specifically fish scales and vertebrae. This direct physical evidence confirmed that the animal’s diet was not purely plant-based. The presence of fish remains inside the stomach provided a clear snapshot of its last meals. This combination of stones for grinding plants and scales from fish confirmed its omnivorous nature.
The Specialized Omnivore Diet
Synthesizing the physical and internal evidence reveals Deinocheirus as a highly specialized, semi-aquatic omnivore. It lived in the Nemegt Formation, a region characterized by river systems, swamps, and mudflats, similar to modern delta environments. The duck-like beak and weak bite force were perfectly suited for siphoning or scooping up soft aquatic plants and tubers from the water and riverbanks.
The fish remains confirm that its diet was supplemented by small, slow-moving aquatic life. Its long arms and blunt claws likely helped it gather these food sources, perhaps by wading and using its hands to scoop up food or disturb the substrate. This omnivore strategy, involving both soft plant matter and aquatic protein, explains its immense size. Deinocheirus was able to exploit a niche that few other large dinosaurs, like purely herbivorous sauropods or predatory tyrannosaurs, could access.