Byronosaurus jaffei

MAKOVICKY, PETER J., NORELL, MARK A., CLARK, JAMES M. & TIMOTHY, ROWE, 2003, Osteology and Relationships of Byronosaurus jaffei (Theropoda: Troodontidae), American Museum Novitates 3402, pp. 1-32 : 28-30

saurus jaffei ( figs. 14 , 15 ).

Presence of enlarged, distally oriented denticles: Theropod teeth are primitively serrated. In velociraptorine dromaeosaurids there are 5–7 denticles per millimeter ( Currie et al., 1990), while this ratio is 3–3.2 denticles per millimeter in Dromaeosaurus albertensis (Currie, 1996) . By contrast the number of denticles is 2.3– 3 in Saurornithoides mongoliensis ( Russell, 1969) and less than 2 per mm in Troodon formosus ( Currie et al., 1990) and Saurornithoides junior (Barsbold, 1974) . In addition, the denticles of these troodontid taxa are long and separated by deep blood grooves with small proximal blood pits. The teeth of Sinornithoides youngi have porportionately smaller serrations than do those of the three larger taxa listed above, but they are still proportionately large relative to tooth size ( Currie and Dong, 2001a).

Relationships between Byronosaurus jaffei , Sinornithoides youngi , and a clade comprising the three larger bodied taxa Troodon formosus and both species of Saurornithoides cannot be parsed out, partly because the braincase is undescribed for Sinornithoides and the dentition is autapomorphic in Byronosaurus jaffei . The Troodon + Saurornithoides clade is derived in its possession of a medially deflected symphysis on the dentary and by the secondary loss of a dorsal tympanic recess.

ACKNOWLEDGMENTS

We thank the field crews of the 1993, 1994, and 1996 field seasons. For help in Mongolia, we would especially thank D. Baatar, T. Boldsukh, D. Dashzeveg, and R. Barsbold. Mike Novacek found the type specimen ( IGM 100 /983). Martin Kundrát carefully went over the manuscript. Amy Davidson and Bill Amaral prepared the specimens and Mick Ellison developed the figures. This work was supported by the Division of Paleontology at the American Museum , the Field Museum Department of Geology, and the Jaffe Family Foundation .

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Figures

Fig. 14. Stereopairs of the braincase of the holotype specimen IGM 100/983. Top, posterior; middle, anterior; lower, right lateral views. Abbreviations are listed in appendix 1.

Fig. 15. The braincase of the holotype specimen IGM 100/983. Top, left lateral; middle, ventral; lower, dorsal views. Abbreviations are listed in Appendix 1.