The Number of Substantial Finds of Tyrannosaurus rex
Horner and Lessem (1993) reported that there were 11 substantial T. rex finds known at that time. Arguably there was a twelfth, that being USNM 6183, a specimen originally referred to as Ornithomimus grandis but now thought to be a young specimen of T. rex. (Gilmore, C. W. Osteology of the carnivorous Dinosauria in the United States Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus. Bull. U.S. Natl. Mus. 110, 1-154 ).
There is no one accepted means to assess body mass in dinosaurs be it through volume displacement from “scale” models, computerized volume estimates from drawings, or direct skeletal measures (Seebacher, F. A new method to calculate allometric length-mass relationships of dinosaurs. J. Vert. Paleo. 21, 51-60 ). Each has its own uncertainties, be it inferences about visceral tissues, linear measures (e.g. length is not known for T. rex(Brochu, C. A. Osteology of Tyrannosaurus rex: Insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. J. Vert. Paleo. Mem. (7) 22, 1-138 ), artistic license, etc. Femoral circumference measures may underestimate the mass of non-avian dinosaurs(Carrano, M. T. Implications of limb bone scaling, curvature and eccentricity in mammals and non-avian dinosaurs. J. Zool. Lond.254, 41-55 ) but is the only tenable method here since the others have not been applied to all 20 of the ontogenetic series specimens we studied. The range of sizes for an adult T. rex similar to our RTMP 81.12.1 (est. mass 5,040 kg) ranges from 4,500-7,500 kg (mean = 6235) using these methods (Seebacher reference above). Should one of these other methods prove more accurate, the estimates here, being scientifically derived, can be adjusted accordingly, but the conclusions about the heterochronic means by which T. rex attained gigantism should not be affected.