Paleontologists have identified over 1,000 species of dinosaurs ranging in age from about 230 to about 66 million years ago. This represents only a fraction of the total number of dinosaur species that ever lived. Most species are known only from a single bone or tooth. In a few cases, we have a partial skeleton, and in even fewer do we have a complete skeleton. In only a handful of cases do we have more than one skeleton of a dinosaur species.
In the United States, one of the best geological formations for finding dinosaurs is the Hell Creek Formation. Rocks of the Hell Creek Formation mostly appear at the surface in North and South Dakota and uin Montana. The rock which makes up the Hell Creek Formation were laid down at end of the Cretaceous Period, about 68 to 66 million years ago. Tyrannosaurus rex, Triceratops, Edmontosaurus, and Ankylosaurus were all found in the formation. Researchers have also unearthed hundreds of single bones and teeth in the Hell Creek fossil beds, most of which remain unidentified.
Now, the story.....
In 1924, Smithsonian Institution dinosaur hunter Charles Whitney Gilmore found a pair of disembodied hands in the Hell Creek Formation. He named it Chirostenotes, or "Narrow Hands". A Canadian paleontologist found a toothless mandible in 1940 from Alberta. He named it Caenagnathus and thought it was a bird. In 1976, a Polish researcher concluded that Caenagnathus was likely an animal as the Oviraptoridae, a group of predatory dinosaurs with parrot-like heads discovered in Mongolia and China in 1924 by Henry Fairfield Osborn. Partial skeletons of Caenagnathus-like dinosaurs were found in Alberta, which supported the Polish scientist's conclusions.
Dinosaur expert Hans-Dieter Sues added another chapter to the story in 1997. Sues was looking at the thousands of dinosaur fossils collected in the late 1800s and first two decades of the 1900s by fossil hunters. Few of these had ever been unpacked, and many remained in their original plaster casts. One of these was a partial skeleton collected in 1923. After cracking open the plaster jacket and freeing the fossil bone from the rock surrounding it, Sues realized it, too, was Chirostenotes.
The final clues were discovered 1998, when commercial fossil hunter Fred Nuss excavated two partial skeletons of a large, bird-like dinosaur from the Hell Creek Formation at a site in Harding County, South Dakota. Carnegie Museum of Natural History in Pittsburgh, desirous of beefing up its collection of Cretaceous dinosaurs, bought them both.
Matt Lamanna, curator of dinosaurs at the Carnegie Museum, asked Sues to help study the two skeletons. Lamanna and Sues learned that graduate students Tyler Lyson and Emma Schachner were studying yet a third skeleton of a Caenagnathus-like dinosaur. This less-complete skeleton had been found in the Hell Creek Formation in North Dakota by Tyler (although I can't find the date for this discovery).
Realizing that pieces of a dinosaur might be here, might be there, might be in another place, the four scientists pooled their specimens. Once the pieces were put together, they realized they didn't have a Chirostenotes -- they had a Caenagnathus.
Four genus of Caenagnathus had already been identified (Caenagnathasia, Elmisaurinae, Epichirostenotes, and Nomingia). But they realized they had a fifth, completely new genus: Anzu. The researchers called the type-species Anzu wyliei. Anzu is a winged minor deity in Mesopotamian mythology, and Wylie is the name of the dinosaur-obsessed grandson of two mega-wealthy donors to the Carnegie Museum.
Because the Caenagnathus found in China and Mongolia had feathers, the scientists inferred that the North American genus had them, too.
The scientists announced their discovery in March 2014.