ERICKSON, Gregory, M.; Florida State University: Comparison of exponential-stage growth rates between non-avian dinosaurs and extant vertebrates and its bearing on the evolution of avian growth rates

The comparison of growth rates between major vertebrate clades is typically achieved by comparing regressions of exponential-stage growth standardized to body mass. Actinopterygian fish and non-avian reptiles have been shown to have relatively slow growth rates, marsupials moderate rates, while birds and eutherian mammals grow at rapid rates. The three competing hypotheses for how non-avian dinosaurs grew are modeled on each of these patterns. Comparison of growth rates in living taxa to those of dinosaurs has been hindered by uncertainties regarding maximal growth rates during ontogeny. Using a new method called Developmental Mass Extrapolation (DME) my colleagues and I have reconstructed growth curves for various dinosaurs by coupling estimates of mass and longevity throughout development. The results suggest that dinosaurs exhibited S-shaped growth curves typical of most vertebrates and that dinosaur growth did not conform to any of the previously posited patterns (i.e. they had a trajectory unique unto themselves). All non-avian dinosaurs grew at rates that are accelerated relative to the primitive condition seen in extant reptiles. Small dinosaurs grew at moderately rapid rates similar to those of marsupials, but large species attained rates comparable to those of eutherian mammals and precocial birds. Growth in giant sauropods was similar to that of whales of comparable size. Non-avian dinosaurs did not attain rates like those of altricial birds. Avian growth rates were attained in a step-wise fashion after birds diverged from theropod ancestors in the Jurassic period.