Tyrannosaurus rex, Osborn, 1905

Donald M. Henderson & Eric Snively, 2004, Tyrannosaurus en pointe: allometry minimized rotational inertia of large carnivorous dinosaurs, Proceedings of the Royal Society, Series B 271, pp. 57-60 : 58

3 . RESULTS

(a) RI scaling of theropods and quadrupedal carnivorous archosaurs

Least-squares regression of log-transformed data (table 1) indicates that theropod RI scaled to mass with an exponent of 1.546 and an intercept of ― 1.630, whereas in the quadrupedal forms RI scaled to mass with an exponent and intercept of 1.624 and ― 1.630, respectively. These slopes are significantly different (t -test, p <0.016), and that of the quadrupedal archosaurs is closer to the value of 1.667 predicted from geometric similarity. Plotting RI against body mass ( figure 2 ) highlights the reduction of RI at large body size in theropods, despite the apparently small difference in their scaling coefficient from that of non-dinosaurian forms. Dramatically, the 5.7 tonnes (t) Acrocanthosaurus atokensis has only 43% of the RI predicted from isometric scaling, and this diminishes to 36% in the 10 t Tyrannosaurus rex . This 10 t estimate is greater than those for other specimens of T. rex ( Henderson 1999) , but because mass is proportional to the cube of length, the greater length of Field Museum of Natural History specimen FMNH PR2081 (we measured it at 12.01 m) results in a substantially larger body mass. As Tyrannosaurus is almost twice the mass of the next heaviest animal, Acrocanthosaurus , T. rex could potentially act as an outlier and distort the identified scaling relationship. However, exclusion of T. rex from the regression analysis resulted in trivial changes in the slope and intercept values (to 1.545 and ― 1.629, respectively).

Figures

Figure 2. RI versus body mass in carnivorous archosaurs. Grey bands indicate the range of changes in RI magnitudes when computed with body widths that were 110% and 90% of the original models.