Tyrannosaur ageing

Abstract

Rate of ageing in tyrannosaurs was calculated from parameters of Weibull functions fitted to survival curves based on the estimated ages at death of fossilized remains. Although tyrannosaurs are more closely related to birds than to mammals, they apparently aged at rates similar to mammals of comparable size. Rate of growth in body mass of tyrannosaurs was similar to that of large mammals, and their rates of ageing were consistent with the estimated extrinsic mortality, which is strongly correlated with the rate of ageing across birds and mammals. Thus, tyrannosaurs appear to have had life histories resembling present-day large terrestrial mammals. Rate of ageing in warm-blooded vertebrates appears to be adjusted in response to extrinsic mortality and potential lifespan, independently of both physiological and developmental rates. However, individuals in species with the slowest rates of ageing suffer the highest proportion of ageing-related mortality, hence potentially strong selection to further postpone senescence. Thus, the longest observed lifespans in birds, tyrannosaurs and mammals might be close to the maximum possible.

Figure 1

The logarithm of the proportion of individuals surviving as a function of age based on ages at death of 22 fossilized specimens of Albertosaurus sarcophagus (data from Erickson et al. 2006). The fitted Weibull curve is indicated by the solid line.

Figure 2

Rate of ageing as a function of (a) body mass and (b) initial mortality rate. Bird and mammal data from appendix tables A1 and A2 in Ricklefs (1998).