ARTICLE A NEW TROODONTID (DINOSAURIA: THEROPODA) FROM THE CENOMANIAN OF UZBEKISTAN, WITH A REVIEW OF TROODONTID RECORDS FROM THE TERRITORIES OF THE FORMER SOVIET UNION ALEXANDER O. AVERIANOV 1 and HANS-DIETER SUES *,2 1 Zoological Institute, Russian Academy of Sciences, Universitetskaya nab 1, Saint Petersburg 199034, Russia, lepus@zin.ru; 2 National Museum of Natural History, Smithsonian Institution, MRC 106, P.O. Box 37012, Washington, DC 20013-7012, U.S.A., suesh@si.edu ABSTRACT—Based on a review of troodontid specimens from the territories of the former Soviet Union, including new discoveries from Uzbekistan, two dental morphotypes can be distinguished among Troodontidae from the Cretaceous of Asia: (1) unserrated teeth, present in Mei from Lujiatun (China; Early Cretaceous: Hauterivian-Barremian), an unnamed taxon from Hövöör (Mongolia; Early Cretaceous: Aptian-Albian), Urbacodon itemirensis, gen. et sp. nov. from Itemir and Urbacodon sp. from Dzharakuduk (Uzbekistan; Late Cretaceous: Cenomanian and Turonian, respectively), and Archae- ornithoides from Bayn Dzak and Byronosaurus from Ukhaa Tolgod (Mongolia; Late Cretaceous: Campanian); and (2) serrated teeth, present in Sinornithoides from Huamuxiao (China; Early Cretaceous) and Sinornithoides-like taxa from Khamryn Us (Mongolia; Early Cretaceous: Aptian-Albian), Shestakovo (Russia; Early Cretaceous: Aptian-Albian), and Sheikhdzheili (Uzbekistan; Late Cretaceous: Cenomanian); Troodontidae indet. from Kansai (Tajikistan; Late Creta- ceous: Santonian) and Alymtau (Kazakhstan; Late Cretaceous: Campanian), Saurornithoides (Mongolia and China; Late Cretaceous: Campanian-Maastrichtian), and Troodon from Kakanaut and Blagoveshchensk (Russia; Late Cretaceous: Maastrichtian). INTRODUCTION Troodontid theropods are among the rarest dinosaurs in the fossil record. Nine troodontid genera are currently recognized (Makovicky and Norell, 2004; Xu and Norell, 2004; Xu and Wang, 2004), with only Troodon formosus being represented by relatively abundant material from Campanian- to Maastrichtian- age strata in western North America (e.g., Sternberg, 1932; L. S. Russell, 1948; D. A. Russell, 1969; Sues, 1977; Currie, 1985, 1987, 2004; Wilson and Currie, 1985; Currie and Zhao, 1994). Troodontidae have numerous bird-like features, and study of this group has substantially contributed to our understanding of the origin of birds (e.g., Currie, 1987; Varricchio, 1993, 1997; Varricchio et al., 1997, 1999, 2002; Xu et al., 2002b; Makovicky et al., 2003; Varricchio and Jackson, 2004; Xu and Norell, 2004). With the exception of Troodon, all named troodontid genera and at least one unnamed taxon are endemic to Asia (Osborn, 1924; Barsbold, 1974; Barsbold et al., 1987; Osmólska, 1987; Barsbold and Osmólska, 1990; Kurzanov and Osmólska, 1991; Elzanowski and Wellnhofer, 1992, 1993; Currie and Peng, 1994; Russell and Dong, 1994; Varricchio, 1997; Norell et al., 2000; Currie and Dong, 2001; Xu et al., 2002b; Makovicky et al., 2003; Makovicky and Norell, 2004; Xu and Norell, 2004; Xu and Wang, 2004). Troodon is now known from both western North America and the Far East of Russia. Despite this impressive list of taxa, we intend to demonstrate in this paper that the diversity of troodon- tids in Asia has been underestimated. Recent discoveries indi- cate that two dental morphotypes were present among Creta- ceous Troodontidae from Asia, one with serrated and the other with unserrated teeth. In this article, we describe a new troodontid with unserrated teeth from the Cenomanian-age Itemir locality in the central Kyzylkum Desert, Uzbekistan. A similar species is also repre- sented at the nearby Turonian-age locality Dzharakuduk. The Itemir-Dzharakuduk depression contains strata of several Cre- taceous formations that span the time interval from the Aptian- Albian to the Santonian (Fig. 1; Pyatkov et al., 1967; Sochava, 1968; Martinson, 1969; Nessov, 1995, 1997; King et al., in press). The first dinosaurian bones from Dzharakuduk were collected in 1914 by the Russian geologist A. D. Arkhangelsky (Arkhangel- sky, 1916; Riabinin, 1931). During the 1930s, the locality was repeatedly visited by geologists (Sosedko, 1937). The best find made during that period was a complete turtle shell, the holotype of Lindholmemys elegans Riabinin, 1935. In 1958, A. K. Ro- zhdestvensky visited the Itemir-Dzharakuduk depression and made collections (Rozhdestvensky, 1964). Unfortunately, he er- roneously claimed that Dzharakuduk (Bissekty) and Itemir rep- resented the same locality, whereas these two sites are actually separated by several kilometers, expose Cretaceous strata of dif- ferent ages (Albian-Cenomanian at Itemir and Turonian- Santonian at Dzharakuduk), and have yielded different verte- brate assemblages (Nessov, 1997). Rozhdestvensky’s claim was accepted by Kurzanov (1976), who applied the generic nomen Itemirus to a new taxon of theropod dinosaur based on a brain- case from Dzharakuduk that was collected by Rozhdestvensky in 1958. The erroneous synonymy of the two localities, Itemir and Dzharakuduk, is still occasionally repeated in the secondary lit- erature (e.g., Unwin and Bakhurina, 2000). Compounding the confusion is the fact that the richest vertebrate-bearing level at the Itemir locality, producing the holotype of the new troodontid described herein, is stratigraphically situated in the Cenomanian Dzharakuduk Formation (Martinson, 1969), a designation that * Corresponding author. Journal of Vertebrate Paleontology 27(1):87–98, March 2007 © 2007 by the Society of Vertebrate Paleontology 87