Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or without bony crests atop the head. They ranged in size from Caudipteryx, which was the size of a turkey, to the 8-meter-long, 1.4-ton Gigantoraptor. The group (along with all maniraptoran dinosaurs) is close to the ancestry of birds. Some researchers such as Maryanska et al (2002) and Osmólska et al. (2004) have proposed that they may represent primitive flightless birds. The most complete oviraptorosaur specimens have been found in Asia. The North American oviraptorosaur record is sparse. The earliest and most basal ("primitive") known oviraptorosaurs are Ningyuansaurus wangi, Protarchaeopteryx robusta and Incisivosaurus gauthieri, both from the lower Yixian Formation of China, dating to about 125 million years ago during the Aptian age of the early Cretaceous period. A tiny neck vertebra reported from the Wadhurst Clay Formation of England shares some features in common with oviraptorosaurs, and may represent an earlier occurrence of this group (at about 140 million years ago). Description Oviraptorosaurians have shortened rostrums, massive, beaklike mandibles, and long parietal bones. With the exception of the 8-meter long Gigantoraptor, they are generally medium-sized and rarely exceeded 2 meters in length. The most primitive members have four pairs of teeth in the premaxillae, such as in Caudipteryx and in Incisivosaurus they are enlarged and form bizarrely prominent bucktoothed incisors. The more advanced members have no teeth in the jaws. Pneumatization is extensive in the skulls and vertebrae of the more advanced members. Oviraptorosauria have thick, U-shaped furculae and a large sternal plates that are wider (together) than they are long, unlike in birds and dromaeosaurs. The arms are around half the length of the legs and over half the length of the presacral vertebral column. The hands are long, and tridactyl, with a reduced third finger in Caudipteryx and Ajancingenia. There are between 5 and 8 sacral vertebrae. The pubis is vertical or subvertical, with a concave anterior edge. The tibia is 15%-25% longer than the femur. The tail is short, with the number of vertebrae reduced to 24 or so, and proximally very thick, with broad transverse processes. The ischium retains the primitive character of a prominent, triangular obturator process and lack the proximodorsal process that is found in birds. In advanced oviraptorosaurians,