Anzu

Anzu (named for Anzû, a bird-like daemon in Ancient Mesopotamian religion) is a monospecific genus of caenagnathid dinosaur from North Dakota, South Dakota and Montana that lived during the Late Cretaceous (upper Maastrichtian stage, 67.2-66.0 Ma) in what is now the Hell Creek Formation.[1] The type species and only species, Anzu wyliei is known from numerous skeletons that preserve cranial and postcranial elements.[1] It was named in 2014 by Matthew C. Lamanna, Hans-Dieter Sues, Emma R. Schachner, and Tyler R. Lyson.[1]

Anzu was listed as one of 2014’s "Top 10 New Species" discovered, with the findings being of significant scientific value. It was acknowledged again, in 2015, as an unprecedented discovery of scientific worth by the International Institute for Species Exploration.[2][3]

History of discovery

Several large skeletons from the late Maastrichtian Hell Creek Formation of Montana and South Dakota were initially referred to as "cf. Chirostenotes",[4] though more recent studies concluded that they represent new species.[5]

In 1998 Fred Nuss of Nuss Fossils discovered the site containing the holotype, CM 78000. The first two partial skeletons of Anzu were discovered in 1998 by Fred Nuss Fossils on a private South Dakota ranch.[6][1][7] The two specimens weren't buried together – the skeletons rested about 330 feet apart with the second individual in a rock layer about 11 feet below the first – but, once prepped by the commercial outfit Triebold Paleontology, it was clear that both represented the same dinosaur.[8][citation needed] Both were mostly disarticulated and appeared to have been transported by a water current. A third referred specimen, fragmentary skeleton MRF 319, studied by Tyler Lyson of the National Museum of Natural History, was discovered by Scott Haire, who spotted the bones at his uncle's ranch at Marmarth, North Dakota. A rear lower jaw fragment, FMNH PR 2296, was also referred.[1][9]

These four fossils found at Hell Creek together make up a fairly complete skeleton of Anzu wyliei, comprising about 75 to 80 per cent of the whole skeleton.[9] Three researchers, Emma Schachner of the University of Utah, Matthew Lamanna of the Carnegie Museum of Natural History and Tyler Lyson of the Smithsonian in Washington realized in 2006 that they each had partial skeletons of the same species and began collaborating to study it, assisted by Hans-Dieter Sues, a paleontologist at the National Museum of Natural History of the Smithsonian Institution in Washington.[9] The main fossils are being held at the Carnegie Museum of Natural History in Pittsburgh.[10]

The genus is notable as the first well-preserved example of a North American oviraptorosaur. According to Sues, "for almost a hundred years, the presence of oviraptorosaurs in North America was only known from a few bits of skeleton, and the details of their appearance and biology remained a mystery. With the discovery of A. wyliei, we finally have the fossil evidence to show what this species looked like and how it is related to other dinosaurs."[10]

The creature's appearance – "big crests on their skulls, a beak, no teeth, and a very bird-like skeleton"[10] – and its discovery in the Hell Creek Formation led to it being jokingly nicknamed the "chicken from hell". Matthew Lamanna, who devised the species' name, originally wanted to use a Latin or Greek version of "chicken from hell". However, he found that this nickname does not translate well in those languages, so he eventually settled on evoking and using the name of the bird-like daemon Anzu from the mythology of ancient Sumer,[11] which itself roughly translates to "heavenly eagle".[12] The specific name, wyliei, honors Wylie J. Tuttle, the grandson of one of the museum's donors, Lee B. Foster.[1]

Anzu wyliei is characterized by a toothless beak, a prominent crest, long arms ending in slender, relatively straight claws, long powerful legs with slender toes, and a relatively short tail. Anzu measured about 3.5–3.75 metres (11.5–12.3 ft) long, up to 1.5 metres (4.9 ft) tall at the hips and 200–300 kilograms (440–660 lb) in body mass, and was among the largest North American oviraptorosaurs.[1][13][14]

When the type specimen of Anzu was described, several autapomorphies (derived traits unique to a genus) were established. There is a high crescent-like crest on the skull, formed by the upper branches of the praemaxillae. The occipital condyle is wider than the foramen magnum. The front part of the lower jaw, which is fused with its counterpart, has a prominent flange on its outer side. The retroarticular process, a prominent projection at the rear of the lower jaw, is elongated, about as long as the jaw joint surface. The lower end of the radius is divided into two rounded processes. The first phalanx of the second finger has a trough along the lower edge of its inner side. The front side of the astragalus (ankle bone) has a tubercle at the base of its ascending process.[1]

An additional four possible autapomorphies were identified in the referred specimens. The main body of the maxilla has no depression around the antorbital fenestra. The nasal branch of the maxilla is elongated and constructed like an inverted L. The branch of the jugal towards the quadratojugal is vertically deep. The same branch is forked at its rear end.[1]