The independent evolution of gigantism among dinosaurs has been a topic of long-standing interest, but it remains unclear if gigantic theropods, the largest bipeds in the fossil record, all achieved massive sizes in the same manner, or through different strategies. We perform multi-element histological analyses on a phylogenetically broad dataset sampled from eight theropod families, with a focus on gigantic tyrannosaurids and carcharodontosaurids, to reconstruct the growth strategies of these lineages and test if particular bones consistently preserve the most complete growth record. We find that in skeletally mature gigantic theropods, weight-bearing bones consistently preserve extensive growth records, whereas non-weight-bearing bones are remodelled and less useful for growth reconstruction, contrary to the pattern observed in smaller theropods and some other dinosaur clades. We find a heterochronic pattern of growth fitting an acceleration model in tyrannosaurids, with allosauroid carcharodontosaurids better fitting a model of hypermorphosis. These divergent growth patterns appear phylogenetically constrained, representing extreme versions of the growth patterns present in smaller coelurosaurs and allosauroids, respectively. This provides the first evidence of a lack of strong mechanistic or physiological constraints on size evolution in the largest bipeds in the fossil record and evidence of one of the longest-living individual dinosaurs ever documented.
|Original language||English (US)|
|Journal||Proceedings of the Royal Society B: Biological Sciences|
|State||Published - Nov 25 2020|
Bibliographical noteFunding Information:
Data accessibility. Analytical data contained in figures/tables and attached electronic supplementary materials. All project data, including high-resolution thin-section images from sampled specimens, are archived in Dryad Digital Repository . Authors’ contributions. T.M.C. conceived the project, made thin sections, performed histological analyses, performed growth curve analyses, wrote the manuscript and made the figures/tables; J.I.C. collected fossil material, assisted in histological analyses and in writing the manuscript; S.A. collected fossil material and assisted in writing the manuscript; N.D.S. collected fossil material, assisted in histological analyses and in writing the manuscript; D.H. assisted in histological analyses and in writing the manuscript; P.J.M. conceived the project, assisted in histological analyses and wrote the manuscript. Competing interests. The authors declare no competing interests. Funding. Excavation of the Campanas carcharodontosaurid was supported by the National Geographic Society, the Field Museum, and Municipalidad de Villa El Chocón. Excavation and research on Cryolo-phosaurus was supported by the US National Science Foundation awards ANT 0838925 and ANT 1246379. P.J.M.’s current research on fossil vertebrate growth and palaeoecology are supported by NSF awards PLR 1341645 and FRES 1925884. Postdoctoral research support for T.M.C. provided by the Kenneth C. Griffin Fund. Additional fieldwork support provided by the FONCyT—Agencia Nacional de Promoción Científica y Tecnológica Argentina, PICT no. 2014-0564, and National Geographic Grant #9300-13 (to SA). Acknowledgements. We thank the staff of the Field Museum of Natural History (A. Shinya, B. Simpson, A. Stroup) for assistance in destructive sampling and specimen conservation. We thank the staff of the Canadian Museum of Nature, Royal Ontario Museum, Museo Municipal ‘Ernesto Bachmann’, and Paleontological Museum of
© 2020 The Author(s).
- body-size evolution