In 1965, a monster was discovered beneath the Gobi Desert.
Well, actually, only part of a monster. In southern Mongolia, Zofia Kieland-Jaworoska found fossilized remains of an enormous pair of forelimbs buried in the sand.
She also found some vertebrae and a few ribs, but the arms are the center of attention: they're eight feet long with eleven-inch claws. These arms are the stuff of nightmares.
Deinocheirus — pronounced dy-no-KY-rus — is Greek for "terrible hand." The name first appeared when fellow archaeologists Halszka Osmólska and Ewa Roniewicz published a journal outlining the discovery in 1970, so most sources attribute the discovery to that year. But the journal was dated 1969. Summer of love. Of course, Jaworoska really deserves the credit for her efforts in 1965.
Because neither hide nor hair has since been seen of the beast, and because of the dearth of other bones, Osmólska and Roniewicz created a new monotypic family for Deinocheirus — intuitively, the Deinocheiridae — under unranked order Ornithomimosauria. Above Orinthomimosauria is Carnosauria, or meat-eating lizards.
If that's too jumbled, the current taxonomy is as follows:
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Saurischia
Suborder: Theropoda
Infraorder: Coelurosauria
(unranked) Ornithomimosauria
Family: Deinocheiridae
Genus: Deinocheirus
Species: Deinocheirus mirificus
And how has this conclusion been reached?
Well, it took awhile.
At first, scientists assumed that the enormous thick-walled bones were tools for bringing down prey. Osmólska and Roniewicz themselves colorfully posit that the arms were used for "tearing dead or weakly agile prey asunder." 1 Naturally, you find eight-foot arms in the desert, you assume they're for, well, killing. In 1983, D. Lambert excitedly took the description a good few steps further — "[the claws are] horrifying weapons for attacking dinosaurs of almost any size ... capable of ripping open a sauropod's soft underbelly."2
Your moment of zen. A sweet-eyed apatosaur shooting guts everywhere.
The hub of the above taxonomy is Orinthomimosauria. Even though Osmólska and Roniewicz placed the creature in the same order as ostrich-impersonators, it didn't stop people from making it into an enormous tyrannosaurid (Tyro's arms are pathetically small — imagine its size if you magnified it so its arms were the size of Deinocheirus'), even though the structure was an obvious mismatch.
If Deinocheirus is indeed an ostrich-mime, it would have been four times the size of the current largest-known species, Gallimimus. That would give it a length of some forty feet: not much by sauropod standards, but about the size of an average T-Rex. As an orinthomimosaur, it would have been one of the fastest lizards around, likely capable of speeds approaching 50mph. Of course this is hypothesis, since we still haven't found the hind legs.
Even the Deinocheirus' classification as an orinthomimosaur is tenuous. Some posit that the claws are too dull to be good for anything but climbing: the terrible-hand may have been some kind of enormous reptillian sloth.
All we have is arms. Paleontologists are good at what they do, but they can't do much with a pair of arms. Deinocheirus is one of the most enigmatic creatures that ever lived.
Postscript: It was Cretaceous.
1 Osmólska, H. & E. Roniewicz, 1970. Deinocheiridae, a new family of theropod dinosaurs. Palaeontologica Polonica 21: 5-19
2 Lambert, D., 1983. A Field Guide to Dinosaurs. Avon Books, New York.
Other Sources
Wikipedia
http://en.wikipedia.org/wiki/Deinocheirus
Luis V. Rey's Art Gallery: Dinosaurs and Paleontology
http://www.luisrey.ndtilda.co.uk/html/deinonew.htm
Yahooligans!
http://yahooligans.yahoo.com/content/science/dinosaurs/dino_card/132.html
---. The 1987 Childcraft Annual: Dinosaurs!. Childcraft International, Inc. 1987.