Developmental Plasticity in the Life History of a Prosauropod Dinosaur

Abstract

Long-bone histology indicates that the most common early dinosaur, the prosauropod Plateosaurus engelhardti from the Upper Triassic of Central Europe, had variable life histories. Although Plateosaurus grew at the fast rates typical for dinosaurs, as indicated by fibrolamellar bone, qualitative (growth stop) and quantitative (growth-mark counts) features of its histology are poorly correlated with body size. Individual life histories of P. engelhardti were influenced by environmental factors, as in modern ectothermic reptiles, but not in mammals, birds, or other dinosaurs.

Anomalously high variation in postnatal development is ancestral for dinosaurs but lost in birds

“…The Triassic sauropodomorphs Thecodontosaurus antiquus and Melanorosaurus readi have been interpreted as possessing robust/gracile variation in similarly sized limb elements (18,45), but given our interpretation of a similar ostensible dichotomy in early theropods, these taxa probably possess similar levels of variation in growth patterns. As predicted by our results, along with some morphological variation in Plateosaurus engelhardti (46), histological analysis of a large sample of limb elements (n = 33) of Plateosaurus demonstrated that size and histological maturity are poorly correlated in this taxon (22,25). Given the wide distribution of this individual variation in ontogenetic patterns among early-diverging dinosaurs and their closest relatives, this observation suggests that this high variation in both developmental sequence and in body size at skeletal maturity is the ancestral dinosaurian condition (Fig.…”

“…Most studies of the ontogeny of more-derived theropods (15)(16)(17) suggest that the low levels of variation that characterize avian ontogeny were present in close nonavian relatives as well. Closer to the origin of Dinosauria, morphological variation within species is widespread (18)(19)(20)(21)(22)(23)(24)(25)(26), but whether this variation is the result of taxonomic diversity, ontogeny, sexual dimorphism, or simple individual variation is not clear (22,23,27). Furthermore, close dinosaurian relatives or "dinosaur precursors" (e.g., Silesaurus, Asilisaurus) possess high intraspecific variation in growth sequences [i.e., sequence polymorphism (28)], suggesting that this condition could be ancestral for Dinosauria (21).…”

Heterochrony: the Evolution of Development

“…7). Recent research on bone microstructure has shown that many juvenile dinosaurs experienced very rapid growth rates (Padian et al 2001;Sander and Klein 2005), implying that acceleration was the process responsible for the attainment of the peramorphic features. However, studies of theropod growth patterns support the argument that the evolution of very large body sizes of many dinosaurs may have occurred by a combination of both acceleration and hypermorphosis.…”

Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity

“…Meyer 1987;Grant and Dunham 1990;Madsen and Shine 1993;Queral-Regil and King 1998;Wikelski and Thom 2000;Schalk et al 2002;Spencer et al 2006), and could have enabled the adjustment of growth rate to certain environmental and/or physiological conditions in B. galaczi as well. Hence, the growth trajectory of this pterosaur seems to have been more flexible than that of most ornithurine birds, mammals, and some non-avian dinosaurs which are generally thought to show little interindividual variation in growth rate and adult body size (Starck and Ricklefs 1998;Starck and Chinsamy 2002;Sander and Klein 2005).…”

“…On one hand, more complete 2006; Klein and Sander 2008;Horner and Goodwin 2009;Scannella and Horner 2010;Knoll et al 2010;Padian 2013;Shelton et al 2013), because absolute size may not be a true measure of relative ontogeny (e.g., Johnson 1977;Andrews 1982;Galton 1982;Gibson and Hamilton 1984;Brinkman 1988;Bennett 1993;Sander and Klein 2005;). …”