Troodontidae (Dinosauria: Theropoda) from the Upper Cretaceous of Uzbekistan

To date three taxa of troodontid theropod dinosaurs have been recognized from Upper Cretaceous strata in two regions of the Kyzylkum Desert in Uzbekistan. The Cenomanian Khodzhakul Formation in the southwestern Kyzylkum Desert has yielded isolated serrated teeth and some postcranial bones of an indeterminate troodontid. In the central Kyzylkum Desert troodontids are known from the Cenomanian Dzharakuduk Formation ( Urbacodon itemirensis ) and the Turonian Bissekty Formation ( Urbacodon sp.). Urbacodon itemirensis is known from a single dentary whereas Urbacodon sp. is represented by isolated teeth, maxilla and dentary fragments, a partial braincase, and some postcranial bones. The troodontid affinities of Urbacodon are supported by several synapomorphies: presence of a subotic recess; reduced basal tubera placed directly under the occipital condyle; maxilla participating in the margin of the external naris; nutrient foramina on dentary situated within a deep lateral groove; dentary without distinct interdental plates; large number of small dentary and maxillary teeth; teeth constricted between root and crown; anterior dentary teeth smaller, more numerous, more closely spaced than those in the middle of the tooth row, and implanted in a groove; posterior dorsal vertebrae with tall and posterodorsally tapering neural spines; and presence of a midline sulcus on the neural arches of distal caudals. Among Troodontidae, Urbacodon resembles Byronosaurus , Gobivenator , and Xixiasaurus in the absence of serrations on the tooth crowns and having premaxillary teeth that are D-shaped in cross-section. However, phylogenetic analysis did not recover a clade of Asiatic troodontids with unserrated teeth.

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title: A Short-Armed Troodontid Dinosaur from the Upper Cretaceous of Inner Mongolia and Its Implications for Troodontid Evolution
abstract: The Troodontidae represents one of the most bird-like theropod groups and plays an important role in our understanding of avian origins. Although troodontids have been known for over 150 years, few known derived troodontid specimens preserve significant portions of both the forelimb and the hindlimb.  Here, we report a new troodontid taxon, Linhevenator tani gen. et sp. nov., based on a partial, semi-articulated skeleton recovered from the Upper Cretaceous Wulansuhai Formation of Wulatehouqi, Inner Mongolia, China. L. tani has an unusual combination of primitive and derived character states, though our phylogenetic analysis places it in a derived clade within the Troodontidae. As a derived taxon, L. tani has a dromaeosaurid-like pedal digit II, and this species also possesses a humerus that is proportionally much shorter and more robust than those of most other troodontids.  The combination of features present in Linhevenator indicates a complex pattern of character evolution within the Troodontidae. In particular, the discovery of Linhevenator suggests that derived troodontids have independently evolved a highly specialized pedal digit II and have significantly shortened the forelimb over the course of their evolution.

title: THE TAXONOMY OF THE TROODONTID IVPP V 10597 RECONSIDERED
abstract: The partial troodontid hindlimb IVPP V 10597 was originally described as a juvenile Saurornithoides mongoliensis.The present study reconsiders the taxonomic placement of this interesting specimen,given the significant advances in understanding of the Troodontidae that have taken place since it was first described.Morphological comparisons and numerical phylogenetic analyses indicate that V 10597 is more closely related to the sympatric Linhevenator tani than to Saurornithoides mongoliensis,raising the possibility that V 10597 might be a juvenile L.tani.However,V 10597 differs significantly from other troodontids,including L.tani,in numerous hindlimb features and particularly in the proportions of various hindlimb elements.These differences are likely to be taxonomic,and suggest that V 10597 represents a new troodontid.Furthermore,histological analysis indicates that V 10597 is unlikely to be a juvenile of L.tani or any other large troodontid.Based on the available morphological and histological information,we propose the erection of a new taxon,Philovenator curriei gen.et sp.nov.,based on V 10597.This new find increases the known taxonomic diversity and morphological disparity of Late Cretaceous troodontids.

title: A Successive Approximations Approach to Character Weighting
abstract: Fa~ris, J. S. ( 1969. A successive approximations approach to charaaer weighting. Syst. Zool., 18:374385.-Characters that are reliable for cladistic inference are those that are consistent with the true phyletic relationships, that is, those that have little homoplasy. A set of cladistically reliable characters are correlated with each other in a particular non-linear fashion here referred to as hierarchic correlation. Cladistically unreliable characters can be hierarchically correlated only by chance. A technique that infers cladistic relationships by successively weighting characters according to apparent cladistic reliability is suggested, and computer simulation tests of the technique are described. Results indicate that the successive weighting procedure can be highly successful, even when cladistically reliable characters are heavily outnumbered by unreliable ones.