In the summer of 1965, paleontologists working at Altan Uul III in the southern Gobi of Mongolia unearthed gigantic, 2.4-meter-long arms (that’s nearly 8 feet). Based on the forelimbs and a few rib and vertebra fragments, they named the dinosaur Deinocheirus mirificus, a combination of Greek and Latin for “unusual horrible hand.” It remained one of the most mysterious, bizarre dinosaurs until nearly 50 years later, when researchers discovered two more specimens of what turned out to be an ornithomimosaur, or dinos that superficially resemble modern ostriches. This megaomnivore was also humpbacked and had a bit of a "beer-belly." The findings were published in Nature this week.
Working in Mongolia, an international team led by Yuong-Nam Lee from the Korea Institute of Geoscience and Mineral Resources unearthed another Deinocheirus at Nemegt Formation of Altan Uul IV in 2006, and then in 2009, a left forelimb that clearly belonged to Deinocheirus was discovered in a quarry at Bugiin Tsav. This newest specimen is 6 percent longer than the 1965 discovery. However, broken blocks and some money tucked under a rock (as an offering to the gods) indicated that the area had been poached. Eventually, the team recovered its skull, hand, and feet from private collectors, and they finally puzzled together a near-complete animal.
With a body length of 11 meters and an estimated weight of 6,358 kilograms, Deinocheirus is the largest member of Ornithomimosauria, the “bird-mimic lizards.” The 70-million-year-old fossils also brings never-before-seen skeletal features to the group. This includes an elongated snout and a humped back with tall, blade-like spines. The spinal projections probably served as ligament anchors to support the immense weight of its abdomen -- like cable-stayed bridges.
Its scaly, fishy stomach contents and a thousand gastroliths (the stones they swallowed to help with digestion, like with bird gizzards) suggest that Deinocheirus was a megaomnivore that lived in moist environments. And a suite of unique traits demonstrates just how well-suited it was to river system habitats. A toothless, duck-like bill allowed it to nip at soft veggies and forage for food at the bottom of streams, and its deep jaw likely housed a giant tongue for slurping. Meanwhile, flat, blunt-tipped bones under the claws stopped it from sinking into mud. And as for its disproportionately long forearms -- the longest of any bipedal animal ever -- well, they were used for fishing and digging and gathering plants.
“Although the arms have been known since 1965 and have always aroused speculation because of their enormous size and sharp, recurving claws, we were completely unprepared for how strange this dinosaur looks,” study coauthor Philip Currie from the University of Alberta sums up in a news release. “It almost appears to be a chimera, with its ornithomimid-like arms, its tyrannosaurid-like legs, its Spinosaurus-like vertebral spines, its sauropod-like hips, and its hadrosaur-like duckbill and foot-hooves.”
Short hind limbs, broad hips for strong muscle attachments, and large feet indicate that Deinocheirus was a slow mover. Here’s a great, 10-second animation of Deinocheirus walking:
Images: Yuong-Nam Lee/KIGAM (top), Michael Skrepnick (middle)