[N] 2006 New specimens of Gansus yumenensis from the Xiagou formation, China
Harris, J., You, H. & Lamanna, M. (2006) New specimens of the ornithuran bird Gansus yumenensis from the Xiagou formation (Lower Cretaceous) of Gansu Province, China. JVP 26(3) Abstracts pp.72
Spectacular avian fossils from the Lower Cretaceous Jehol Gp. in NE China have provided extensive information on the early evolution of birds, including basal members of the Ornithuromorpha. However, none of these are bona fide members of the Ornithurae sensu Padian (MRCA of Hesperornis regalis and Passer domesticus and all its descendants). In the early 1980’s, slightly younger lacustrine deposits of the Xiagou Fm. (Xinminpu Gp.) in Gansu, NW China, yielded a distal pelvic limb, the holotype of Gansus yumenensis.
The taxon’s incompleteness rendered its affinities doubtful for two decades; however, excavations near the type locality have produced dozens of new, nearly 3D Gansus specimens that present abundant new morphological data. Among the elements, and the data they present, are cervical vertebrae (broad, short, heterocoelous cranially but opisthocoelous caudally in series, low spinous processes, carotid sulcus on caudal elements); thoracic vertebrae (large pneumatic fossae, ventral processes cranially in series, no gastralia); synsacrum (10 or 11 vertebrae); scapula (shorter than humerus, cranially-directed acromion surpassing coracoid tuberculum); coracoid (deep scapular facet, hooked procoracoid process, large lateral process); sternum (apneumatic, sharp apex on carina that spans element, medial & lateral trabeculae, median sulcus, intermuscular lines, four sternal rib facets); humerus (domed head, transverse sulcus, pit on caudodistal end of bicipital crest); ulna (prominent bicipital tubercle); manus (extensor process on alular metacarpal, major metacarpal >2x diameter of minor, major digit phalanx 1 dorsoventrally compressed); pelvis (ilium overlaps caudalmost thoracic ribs, ischium with dorsal process, distal pubes unfused with boot); tibiotarsus (enlarged, proximally-projecting cnemial crests, astragalar ascending process, no supratendinal pons); and tarsometatarsus (intercotylar eminence, extensor sulcus with proximal vascular foramen, unridged hypotarsus, proximoplantarly offset trochlea of metatarsal II, distal vascular foramen).The morphology of many of these elements supports the position of Gansus as an ornithuran.