Skeletal Morphology And Phylogeny Of Jeholornithiformes In Western Liaoning,China

Chaoyang and Jinzhou in western Liaoning,China are important fossil sites for yielding abundant Mesozoic birds.In the past 20 years,several delicate Early Cretaceous Jeholornithiformes specimens have been uncovered there.These specimens,as the main basal birds and only more advanced than the German Archaeopteryx,have provided important evidence for understanding the origin and early evolution of birds for possessing the mosaic characteristics of both theropods and birds.However,the validities of several species are still in doubt and the phylogeny of the whole clade of Jeholornithiformes is in need of further classification.In this dissertation,based on the studies of the holotypes of Shenzhouraptor sinensis,Jixiangornis orientalis,Dalianraptor cuhe and other three new specimens,we recognized two new genera and species:Kompsornis longicaudus and Neimengornis rectusmim,discertained the validities and diagnostic characters of Shenzhouraptor sinensis and Jixiangornis orientalis,regarded Dalianraptor cuhe as a nomon dubium,classified the phylogeny of the clade of Jeholornithiformes,and discussed the evolutionary trend of the compound bones from dinosaurs to birds.Kompsornis longicaudus represents relatively advanced Jeholornithiformes,which diagnosis includes:extremely elongated forelimb and tail;completely fused sternum with a distinctly angular anterolateral corner and stout posterolateral process;coracoid possessing a large supracoracoidal nerve foramen;pelvic girdle completely fused;tibia nearly equal to femur in length;fifth metatarsal absent;ungual of the pedal digit ? largest.Neimengornis rectusmim represents the most primitive Jeholornithiformes,which diagnosis includes:forelimb/hindlimb length=1.09;deltopectoral crest/humerus length=0.27;the minor metacarpal straight with a small intermetacarpal space between the major metacarpal;ungual of the pedal digit ? the largest.The revised diagnosis of Shenzhouraptor sinensis includes:dentary unfused;U-shaped furcula;forelimb/hindlimb length=1.22;deltopectoral crest/humerus length=0.41;a broad manual digit ?-1 and an elongated ungual of the manual digit ?;pubic symphysis completely fused;pedal digit ? not reverse;elongate caudal vertebrae formed by 23-25 centra or more,with rod-shaped middle and posterior vertebrae(ratio of length/height between 3-4).The revised diagnosis of Jixiangornis orientalis includes:dentary with a cripling anteroventral margin;tooth absent on maxilla or mandible;U-shaped furcula with furrow on dorsolateral surface;trumpet-shaped coracoid without foramen;forelimb/hindlimb length=1.3;deltopectoral crest/humerus length=0.38;ungual of the major digit the largest;pubic symphysis not completely fused;ischium with proximodorsal process;pedal digit ? completely reverse;caudal vertebrae formed by about 27 centra,vertebrae significantly elongate after transition point.Based on 516 characters,the phylogenetic analysis of 47 taxa including 7 species of Jeholornithiformes was carried out by TNT 1.5.The strict consensus tree found that Jeholornithi formes were sister groups with Pygostylia,including Jeholornis,Shenzhouraptor,Jixiangornis,Kompsornis and Neimengornis.Both Shenzhouraptor sinensis and Jixiangornis orientalis are independent groups.Neimengornis rectusmim is closer to Archaeopteryx in phylogenetic position,and is the most primitive bird known in Jeholornithiformes at present.Kompsornis longica udus is more advanced,a sister group with prima+Jeholornis curvipes,and represents the earliest avian dinosaur with completely fused pelvic girdle.