New Material Of Similicaudipteryx From The Lower Cretaceous Of Western Liaoning

The Jehol Biota is a significant terrestrial biota of the Cretaceous on the Earth. It is famouswith exquisite fossils of feathered dinosaurs, early birds, early mammals, and early floweringplants. Of these, discoveries of the feathered dinosaurs provide fossil evidences in understandingmajor evolutionary events in origins of the birds, feathers and bird flighting. Among thesefeathered dinosaur groups, Caudipteryx is famous that aroused major arguments in itsrelationship with dinosaurs or birds. With more fossil discoveries and further studies, as a basalgroup of oviraptorosaurians, Caudipteryx has a close relationship with Similicaudipteryx andIncisivosaurus, but the latter two more primitive. Unfortunately, the only known fossil ofIncisivosaurus is an isolated skull and jaws; whereas our knowledge of Similicaudipteryx ismainly limited in postcranial morphology. Therefore, both two taxa need be further confirmed intaxonomy and relationship, as well as their relationships with Caudipteryx.In present study, a nearly complete skeleton of Similicaudipteryx is from the EarlyCretaceous Jiufotang Formation of Chaoyang, western Liaoning. It possibly represents an adultindividual with the largest size as known. The specimen shows the characteristic ofSimilicaudipteryx, such as, antorbital portion shorter than50%of the skull, external naris highlypositioned, teeth present, dentary symphysis “U”-shaped, metatarsal III bilaterally compressed,cuppedicus fossa weakly developed, tail short with sword-like terminal, manual digit3unreduced, hypophysis of dorsal vertebra present. In addition, the specimen provides morevaluable information of Similcaudipteryx, such as, first premaxillary tooth well developed,maxillary tooth present, maxillary process of the jugal band-like and constricted basally,posterior process of the quadratojugal well developed, dorsal vertebrae less than nine, scapularacromion well developed, obturator process well developed. Moreover, Similicaudipteryx showsa similarity with Incisivosaurus in some cranial features, such as nutrient foramen absent alongthe buccal margin, premaxillary tooth incise-like, maxillary tooth present; and different from thelatter in having external naris elongated, obital rim of the jugal tightly curved, squamosal processof the quadratojugal nearly vertical, five premaxillary teeth, posterior premaxillary teeth distallycurved. These differences further support the taxonomic validity of Similicaudipteryx andIncisivosaurus.In addition, a possible mosaic evolution is discussed in Similicaudipteryx, such as, welldeveloped posteroventral process of the quadratojual, and the robust scapular acromion that well known in advanced oviraptorosaurians; whereas, some features are characteristic of primitiveoviraptorosaurians, such as, presence of teeth,“L”-shaped scapulocoracoid, long pubicsymphysis, moderately-sized obturator process. Combined with Similicaudipteryx, the angledextension of the scapulocoracoid appears to be enlarged during the evolution of Oviraptorosauria.Based on the carpal structure of Similicaudipteryx, a possible specialization is discussed incarpus of Caudipteryx.