Justyna SÅowiak, ÂTomasz Szczygielski, ÂMichaÅ Ginter & Åucja FostowiczâFrelik (2020)
Uninterrupted growth in a nonâpolar hadrosaur explains the gigantism among duckâbilled dinosaurs.
Palaeontology (advance online publication)
doi:
https://doi.org/10.1111/pala.12473https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12473Data for this study are available in the Dryad Digital Repository:
https://doi.org/10.5061/dryad.d2547d7z3Duckâbilled dinosaurs (Hadrosauridae) were the most common ornithopods of the Late Cretaceous. Second only to sauropods and in many cases exceeding the sizes of the largest land mammals (such as indricotheres or proboscideans), they are among the largest terrestrial herbivores to have walked the Earth. Despite their gigantic size, diversity and abundance, their growth strategies remain poorly understood. Here, we examine the bone microstructure of several Mongolian hadrosauroids of varied adult sizes. The small and middleâsized species have lines of arrested growth (LAGs). On the other hand, one of the largest duckâbilled dinosaurs, Saurolophus angustirostris, shows uninterrupted growth, comparable with other big hadrosaurs for which the lack of cyclical growth arrests was interpreted as a result of living in the polar region. Since both of the studied taxa inhabited warmer, continental, monsoonâinfluenced environments of the Late Cretaceous Mongolia, we propose that the absence of LAGs is not a climaticâdriven condition but rather connected with the animal's size (i.e. ontogeny). Our results show that, like sauropods, hadrosaurs changed their growth dynamics from cyclical to continuous during their evolution, which made it possible for them to achieve comparable body sizes.