Ben CreislerA new paper with free pdf:====Xiyunykus pengi gen. et sp. nov.ÂBannykus wulatensis gen. et sp. nov.ÂXing Xu, Jonah Choiniere, Qingwei Tan, Roger B.J. Benson, James Clark, Corwin Sullivan, Qi Zhao, Shuo Wang, Hai Xing & Lin Tan (2018)Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution.Current Biology (advance online publication)HighlightsTwo new alvarezsaurian dinosaurs are described from Northwest ChinaThey are intermediate between Late Jurassic and Late Cretaceous alvarezsauriansThey showcase the evolution of highly specialized alvarezsaurian forelimbSpecialized alvarezsaurian forelimb morphology evolved slowly, in a mosaic fashionSummaryHighly specialized animals are often difficult to place phylogenetically. The Late Cretaceous members of Alvarezsauria represent such an example, having been posited as members of various theropod lineages, including birds. A 70-million-year ghost lineage exists between them and the Late Jurassic putative alvarezsaurian Haplocheirus, which preserves so few derived features that its membership in Alvarezsauria has recently been questioned. If Haplocheirus is indeed an alvarezsaurian, then the 70-million-year gap between Haplocheirus and other alvarezsaurians represents the longest temporal hiatus within the fossil record of any theropod subgroup. Here we report two new alvarezsaurians from the Early Cretaceous of Western China that document successive, transitional stages in alvarezsaurian evolution. They provide further support for Haplocheirus as an alvarezsaurian and for alvarezsaurians as basal maniraptorans. Furthermore, they suggest that the early biogeographic history of the Alvarezsauria involved dispersals from Asia to other continents. The new specimens are temporally, morphologically, and functionally intermediate between Haplocheirus and other known alvarezsaurians and provide a striking example of the evolutionary transition from a typical theropod forelimb configuration (i.e., the relatively long arm and three-digit grasping hand of typical tetanuran form in early-branching alvarezsaurians) to a highly specialized one (i.e., the highly modified and shortened arm and one-digit digging hand of Late Cretaceous parvicursorines such as Linhenykus). Comprehensive analyses incorporating data from these new finds show that the specialized alvarezsaurian forelimb morphology evolved slowly and in a mosaic fashion during the Cretaceous.News:https://www.heritagedaily.com/2018/08/how-did- alvarezsaurian-dinosaurs- evolve-monodactyl-hand/121484 ==