Box 4 in Assessing dinosaur growth patterns: a microscopic revolution

Box 4. Comparison of maximal growth rates in dinosaurs to those in extant vertebrates In Figure I, Maximal growth rates for dinosaurs were deduced from age-mass growth curves for six dinosaurs represented by lettered boxes (from smallest to largest: Shuvuuia (Sh), Psittacosaurus (P), SYntarsus (Sy), MassospondYlus (Ms), Maiasaura (Ma) and Apatosaurus (A); [10]). These data were then plotted with similar data for major living vertebrate clades [5]. A regression line was fitted to the dinosaur data spanning the bounds of known dinosaur size. The results show that whole-organism growth rates for dinosaurs were faster than those of living reptiles of equivalent size. This finding supports qualitative conclusions to the same effect based on tissue-level signal and the reasoning underlying Amprino's rule [11,26]. However the data do not conform to theories that dinosaurs grew in the same manner as living birds, mammals [6], or at rates between reptiles and birds and/or mammals [8]. Rather, dinosaur growth rates show a unique scaling trajectory. The regression [Maximal growth rate 0.002215 (M)0.925; R2 0.961] also reveals that small = adult = size in dinosaurs involved decreases in absolute growth rates [10]. One caveat of this being the first plot of its kind is that only a small sampling of species was available at the time. The addition of further data, particularly for large sauropods, where Sander [23] has found what appear to be considerably lower growth rates than those reported by Curry [25], might force reanalysis of the aforementioned trends. (Redrawn and reproduced with permission from [10].)