The sizes of the two animals presented here provide a basis for
further inferences. The broader and more complete tooth of IVPP
V16138 is comparable in size to the largest tooth preserved in the left
maxilla of the fighting Velociraptor (IGM 100/25), which has a skull
length of about 240 mm (Norell et al., 2006: Fig. 6b). The total body
length of the fighting Velociraptor is approximately 1.7 m (Carpenter,
2000), whereas Turner et al. (2007: supplemental information)
estimated the length and mass of an adult specimen of Velociraptor
as 1.5 m and 24 kg respectively. Accordingly, IVPP V16138 and the
fighting Velociraptor were almost certainly both adults, and were of
broadly comparable size. The larger tooth of the Protoceratops IVPP
V16137 has a preserved mesiodistal width of 12.2 mm, and this figure
appears to be up to 25% smaller than the true value as a result of
damage to one side (either mesial or distal) of the tooth (i.e. the tooth
may have been over 16 mm wide). Accordingly IVPP V16137 also
represents an adult individual. To our knowledge, the only published
mass estimates of Protoceratops are the very divergent ones by Colbert
(1962) and Seebacher (2001). Colbert suggested a mass of 177 kg,
probably based on an adult specimen with a body length of
approximately 2 m (Dodson, 1996), while Seebacher calculated
23.7 kg based on an assumed length of 1.4 m. Given the discrepancy
between these figures, a careful reanalysis of the probable mass of
Protoceratops would be valuable.