fi fi fi LETTER a xed, node-based de nition that speci cally excludes Linhe- nykus (2). In their present study, Xu et al. (1) contradicted this by using Parvicursorinae for a more inclusive, branch-based What about European clade that includes Parvicursor (5) but not Patagonykus.This alvarezsauroids? needs to be noted and corrected in subsequent works. Third, Xu et al.’s(1)diagnosisforLinhenykus is currently insufficient to distinguish this taxon from the similarly aged Mongolian Xu et al. (1) reported the alvarezsauroid Linhenykus mono- Parvicursor (5),namedmorethan15yagobyKarhuand dactylus from Inner Mongolia, a confirmed monodactyl Meso- Rautian [Borrisiak Paleontological Institute of the Russian zoic dinosaur. Xu et al.’s (1) phylogenetic hypothesis for Academy of Sciences (PIN) no. 4487/25]. The only difference Linhenykus suggests that it is sister to a clade that includes all clear to us between the overlapping preserved elements of other Cretaceous Laurasian alvarezsauroids. On this basis, these two taxa is a slight discrepancy in size. Xu et al. (1) discussed the paleobiogeographic history of a,1 b Alvarezsauroidea, concluding that the lineage originated in Asia Gareth J. Dyke and Darren Naish a and then spread via successive dispersal events to South and School of Biology and Environmental Science, University College fi b North America [the earliest known record of this lineage is Dublin, Bel eld Dublin 4, Ireland; and School of Earth and En- vironmental Sciences, University of Portsmouth, Portsmouth PO1 from the Jurassic of China (2)]. 3QL, United Kingdom Although there is little doubt that Linhenykus is important and interesting from both phylogenetic and functional stand- 1. Xu X, et al. (2011) A monodactyl nonavian dinosaur and the complex evolution of the points, here, we draw attention to three serious shortcomings of alvarezsauroid hand. Proc Natl Acad Sci USA 108:2338–2342. 2. Choiniere JN, et al. (2010) A basal alvarezsauroid theropod from the early Late Jurassic the study by Xu et al. (1). First, diagnostic alvarezsauroid of Xinjiang, China. Science 327:571–574. remains, although fragmentary, have been described from the 3. Naish D, Dyke GJ (2004) Heptasteornis was no ornithomimid, troodontid, dromaeo- saurid or owl: The first alvarezsaurid (Dinosauria: Theropoda) from Europe. Neues European Cretaceous and are well-documented and corrobo- Jahrbuch Geol Paläontol Monatshefte 2004:385–401. rated (3, 4). Irrespective of their eventual phylogenetic position 4. Csiki Z, Vremir M, Brusatte SL, Norell MA (2010) An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania. Proc Natl Acad Sci USA 107: (awaiting the discovery of better preserved fossils), these spe- 15357–15361. cimens will seriously affect Xu et al.’s (1) paleobiogeogra- 5. Karhu AA, Rautian AS (1996) A new family of Maniraptora (Dinosauria: Sau- rischia) from the Late Cretaceous of Mongolia. Paleontological Journal 30: phic hypothesis. Xu et al. (1) did not discuss the known 583–592. European records of these dinosaurs, except for a passing mention in SI Appendix. Second, Xu et al.’s (1) use of clade names and referral of Linhenykus to Parvicursorinae are in- Author contributions: G.J.D. and D.N. wrote the paper. consistent with their own previous work and will cause confu- The authors declare no conflict of interest. sion. Choiniere et al. (2) originally defined this clade using 1To whom correspondence should be addressed. E-mail: [email protected]. www.pnas.org/cgi/doi/10.1073/pnas.1101602108 PNAS Early Edition | 1of1 Downloaded by guest on September 23, 2021.