Epidexipteryx

Epidexipteryx ("display feather") is a genus of small maniraptoran dinosaur, known from one fossil specimen in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. The specimen is catalog number IVPP V 15471. It has been reported to be a maniraptoran dinosaur from the Middle Jurassic or Upper Jurassic age Daohugou Beds of Inner Mongolia, China (about 152 to 168 mya).

The specific name, Epidexipteryx hui ("Hu's display feather"), and its Chinese name Hushiyaolong ("Hu Yaoming's dragon") were coined in memory of paleomammologist Hu Yaoming.

It is known from a well preserved partial skeleton that includes four long feathers on the tail, composed of a central rachis and vanes. However, unlike in modern-style rectrices (tail feathers), the vanes were not branched into individual filaments but made up of a single ribbon-like sheet. Epidexipteryx also preserved a covering of simpler body feathers, composed of parallel barbs as in more primitive feathered dinosaurs. However, the body feathers of Epidexipteryx are unique in that some appear to arise from a "membranous structure."

In all, the skeleton of Epidexipteryx hui measures 25 centimeters (10 inches) in length (44.5 cm or 17.5 in including the incomplete tail feathers), and the authors estimated a weight of 164 grams, smaller than most other basal avialans.

The skull of Epidexipteryx is also unique in a number of features, and bears an overall similarity to the skull of Sapeornis, oviraptorosaurs and, to a lesser extent, therizinosauroids. It had teeth only in the front of the jaws, with unusually long front teeth angled forward, a feature only seen in Masiakasaurus among other theropods. The rest of the skeleton bore an overall similarity to the closely related Epidendrosaurus, including a hip configuration unusual among other dinosaurs: the pubis was shorter than the ischium, and the ischium itself was expanded towards the tip. However, the tail of Epidexipteryx differed significantly from Epidendrosaurus. In Epidendrosaurus, the tail was long, about 300% of total trunk length, while the short tail of Epidexipteryx was only 70% of its trunk length. The tail of Epidexipteryx also bore unusual vertebrae towards the tip which resembled the feather-anchoring pygostyle of modern birds and some oviraptorosaurs.

Despite its close relationship to avialan birds, Epidexipteryx appears to have lacked remiges (wing feathers), and it likely could not fly. Zhang et al. suggest that unless Epidexipteryx evolved from flying ancestors and subsequently lost its wings, this may indicate that advanced display feathers on the tail may have predated flying or gliding flight.

History of publication
Due to a pre-publication error, a manuscript of the Epidexipteryx hui description first appeared on a preprint Web portal in late September, 2008. The paper was officially published in the October 23rd, 2008 issue of the journal Nature.