MATERIAL AND METHODS

The left mandible of Slaughteria eruptens was scanned at the High-Resolution X-ray Computed Tomography Facility of the University of Texas at Austin. Scanning methods are described in Kobayashi et al. (2002). Three-dimensional reconstructions and sections were made using LightWave 9.3. Slaughteria eruptens has four erupted teeth, two premolars, a deciduous premolar, and a molar. Scanning electron microscopy was done at SMU using the VPSEM Leo-Zeiss 1450VPSE. Size estimates for lower molars of Pappotherium pattersoni and Holoclemensia texana are based on statistical relationships established from published measurements obtained from associated skulls and lower jaws of a series of Cretaceous therian mammals. Single specimens from each of nine Asian Cretaceous tribosphenidan species were used to predict (based on regression coefficients) the lower first (m1) and second (m2) molar anteroposterior lengths (dependent), from corresponding upper molar anteroposterior lengths (independent) (Asiatherium reshetovi, PIN 3907, Szalay and Trofimov 1996; Asioryctes nemegetensis, ZPAL MgM-I/56, Kielan-Jaworowska 1981; Baurunlestes butleri, PIN 3142-701, Kielan-Jaworowska and Trofimov 1980; Deltatheridium pretituberculare tardum, ZPAL MgM-I/91, Kielan-Jaworowska 1975; Kennalestes gobiensis, ZPAL MgM-I/3, Kielan-Jaworowska 1968; Uchkudukodon (Daulestes) nessovi, ZIN 79066, McKenna et al. 2000, Archibald and Averinov 2006; Ukhaatherium nessovi, PSS-MAE 102, Novacek et al. 1997; Zalambdalestes grangeri, ZPAL MgM-I/14, Zalambdalestes lechei, ZPAL MgM-I/13, Kielan-Jaworowska 1968). Different subsets of taxa were used in the M1/m1 and M2/m2 regressions because of missing data. PIN = Institute of Paleontology, Russian Academy of Sciences, Moscow; PM = Field Museum of Natural History, Chicago; PSS-MAE = Paleontological and Stratigraphy Section (Geological Institute), Mongolian Academy of Sciences, Ulaanbaatar; SMU = Shuler Museum of Paleontology, Southern Methodist University, Dallas; ZPAL MgM = Institute of Paleobiology, Polish Academy of Sciences, Warsaw; ZIN = Zoological Institute, Russian Academy of Sciences, Saint Petersburg.