I Know Dino Podcast: Deinocheirus

Episode 10 is all about Deinocheirus, a dinosaur that for 50 years was only known by its giant arms.

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In this episode, we discuss:

The dinosaur of the day: Deinocheirus mirificus, which means “terrible hand”
Deinocheirus lived in the Cretaceous, about 70 million years ago

Only the arms of Deinocheirus were found in 1965 in Mongolia’s Gobi desert (nothing new found until 2009)
For 50 years, all scientists new was that it had giant arms, each 8 feet long, with three 8-inch claws
This lead to many theories: Deinocheirus was a T-rex because of the claws, or a giant sloth-like creature. It may have been over 100 feet long

Dr. Yuong-Nam Lee from the Korea Institute of Geoscience & Mineral Resources and his team (which included Dr. Phil Currie, from Episode 4: Tarbosaurus) found two well-preserved specimens. According to Lee, “they tell us Deinocheirus was much weirder than anyone could have imagined.”
Lee and his team found Deinocheirus in August 2009 at Mongolia’s Nemegt Formation. Poachers had already taken bones from the site but they found the left arm of a Deinocheirus and a mostly complete skeleton (though it was missing parts of its spine, right arm, and hands)
Currie, said their team always investigated looted quarries, in case they found anything of significance. In 2011, a Belgian scientist called Currie because he thought he had found the missing Deinocheirus fossils. It turned out to be from the same specimen they had found in 2009.

Dr. Tsogtbaatar Chinzorig of the Mongolian Academy of Sciences’ Paleontological Center and his colleagues analyzed and put together the fossils.
Deinocheirus was described in Nature journal in 20
Originally Deinocheirus was classified as a carnosauria, in the theropod group. But now it’s considered a primitive ornithomimosaurian, related to the Garudimimus and Beishanlong, in the family Deinocheiridae

Both Deinocheirus and Spinosaurus are examples of dinosaurs that look completely different from what scientists thought
Because of how unique Deinocheirus actually looks, Lee said this is “a true cautionary tale in predicting body forms from partial skeletons.”
The dinosaur has been likened to Jar Jar from Star Wars. It was big and slow, with a horse like head and hump back.

Deinocheirus wass 35 feet long and 6 tons, almost as big as T-rex. But it did not have a strong bite. Instead it had a duck like snouth with no teeth
It walked upright with 6-feet long arms out in front. Its head was 3 feet long
Deinocheirus had a narrow body. It had ten neck vertebrae that were low and long, each one was shorter the further away it was from the skull. This means Deinocheirus had an S-curved back, because it had such a large skull

Deinocheirus had 12 back vertebrae, with the longest one in the back (at 8.5 times the height of the centrum). This is almost as high as the ratio of neural spines in Spinosaurus
Dr. Chinzorig said Deinocheirus had tall dorsal spines like Spinosaurus, truncated hoof-like claws on the feet (so it wouldn’t sink in muddy ground) and bulky hind legs like tyrannosaurids, with sauropod-like hips, and a hadrosaur-like duckbill
Deinocheirus also had thick bony spines that stuck up from its backbone, which gave it a sail structure (though it was thicker than the sail of Spinosaurus)

Deinocheirus has also been described as having a camel-like hump and neck of an ostrich
Its round, flat beak was covered in keratin
Its lower jaw was much bigger and deeper compared to its slender upper jaw (upper jaw similar in size to tyrannosaur)

Deinocheirus blunt, short claws were similar to the therizinosaur Alxasaurus, which used the claws for digging and gathering plants
The team also found that Deinocheirus‘ tail was fused into a pygostyle, which supports tail feathers in modern birds. So it probably had a fan of tail feathers
Deinocherius is technically an ornithomimosaur (ostrich-like dinosaur), which are known for being fast, but Deinocheirus is too big

Most ostrich-like dinosaurs were only a little bigger than humans, so the evolving into such a giant is probably why it looked so strange
Scientists found bite marks which they think means Deinocheirus was prey for Tarbosaurus
Dr. Currie said its size probably helped protect it from Tarbosaurus

Deinocheirus was probably a megaomnivore (ate everything)
Deinocheirus probably ate soft plants, especially ones that grew at the bottom of streams and lakes. It probably used its duck bill to get at them, and then sucked up the plants with its big tongue inside its large lower jaw. To gring up its food, it swallowed stones (like ostriches and other modern birds)
Lee and his team found over 1,400 of these stones, called gastroliths, inside the Deinocheirus specimens they discovered

The team also found fish remains, but which means Deinocheirus was often in fresh water and could eat anything (including fish, small vertebrates, and plants). It’s been described as a “garbage-disposal” type of dinosaur that probably used its large hands to dig for food or pull down branches
Deinocheirus is one of the largest ornithomimosaurs, but it had hollow bones to keep it lighter. Of bipedal dinosaurs, it had the largest arms
Deinocheirus could not run (unlike other ornithominosaurs)

Deinocheirus was probably diurnal
Its brain size compared to its body was low and similar to sauropods (unlike other ornithomimosaurs that had proportional sized brains)
Deinocheirus is part of the family Deinocheiridate, which lived 115 to 69 million years ago

The family was named because of Deinocheirus‘ unique arms. Originally scientists thought Deinocheirus was a carnosaur, and the only other carnosaurian from the same time period in Mongolia was Tarbosaurus
Deinocheiridate is part of the group ornithomimosaurus (ostrich dinosaurs)
Ornithomimosaur skulls were small, with large eyes and slender necks. Most had toothless beaks, though some primitive species had teeth

Ornithomimosaurs had long arms with powerful claws, and long hind limbs with strong toes and hooflike claws. They were probably the fastest dinosaurs, and they had feathered, not scaly, hides
Ornithomimosaurs ate plants and many have been found with gastroliths in their stomachs. They were very abundant, though some may have been omnivores that also ate small animals
Ornithomimosaurs may have been cathemeral, which means active during the day at short intervals (unlike the diurnal Deinocheirus)

Fun fact: Based on dinosaur bone structure, scientists believe dinosaurs lived to be between 75 and 300 years old

I Know Dino Podcast: Deinocheirus (Episode 10)