A short-armed dromaeosaurid from the Jehol Group of China with implications for early dromaeosaurid evolution

Abstract

Recent discoveries of basal dromaeosaurids from the Early Cretaceous Jiufotang and Yixian formations of Liaoning, China, add significant new information about the transition from non-avian dinosaurs to avians. Here we report on a new dromaeosaurid, Tianyuraptor ostromi gen. et sp. nov., from the Early Cretaceous Yixian Formation of western Liaoning, China, based on a nearly complete skeleton. Tianyuraptor possesses several features only seen in other Liaoning dromaeosaurids, although to a less developed degree, and it also exhibits features unknown in Laurasian dromaeosaurids but present in the Gondwanan dromaeosaurids and basal avialans, thus reducing the morphological gap between these groups. Tianyuraptor possesses a comparatively small furcula and proportionally short forelimbs. This lies in stark contrast to the possible capacity for flight in the microraptorines, which have proportionally long and robust forelimbs and large furculae. The presence of such striking differences between the Early Cretaceous Jehol dromaeosaurids reveals a great diversity in morphology, locomotion and ecology early in dromaeosaurid evolution.

A new raptorial dinosaur with exceptionally long feathering provides insights into dromaeosaurid flight performance

“…The forelimb is long with respect to the hindlimb; its total length (including digit II) is 96% of the hindlimb (including digit III). This ratio contrasts with the shorter forelimbs of other Jehol dromaeosaurids (53% in Tianyuraptor ostromi, 75% in Sinornithosaurus millenii and 89% in Microraptor zhaoianus) 3,12,13 . The humerus is significantly longer than the radius-ulna (420%), as opposed to Sinornithosaurus millenii and Microraptor zhaoianus in which these elements are subequal 3,12 .…”

Unenlagiinae revisited: dromaeosaurid theropods from South América

“…On the other hand, in Deinonychus, Bambiraptor, Luanchuanraptor, Tianyuraptor, Mahakala, in troodontids such as Sinovenator and Anchiornis, and in basal birds such as Archaeopteryx, Jeholornis, and Confuciusornis, the dorsal rim of the postacetabular blade is convex and continuous with the dorsal rim of the preacetabular blade, without the presence of any point of inflection (Ostrom 1969, 1976b, Wellnhofer 1974, 1992, Chiappe et al 1999, Burnham et al 2000, Elzanowski 2002, Paul 2002, Zhou and Hou 2002, Zhou and Zhang 2002. Burnham 2004, Lü et al 2007, Turner et al 2007, Hu et al 2009, Zheng et al 2010. Furthermore, in Microraptor, Hesperonychus, and Archaeopteryx a supratrochanteric process is also present (Ostrom 1969, 1976b, Wellnhofer 1974, 1992, Elzanowski 2002, Hwang et al 2002, Longrich and Currie 2009).…”

Vertebrate diversity of the Jehol Biota as compared with other lagerstätten

“…The Jehol theropods represent nearly all major Cretaceous lineages, and many are feathered, characteristic of the appearance of many arboreal or herbivorous forms [27][28][29][30].…”