Early growth dynamics of titanosaur sauropods inferred from bone histology

Abstract

Histological studies have proven to be a powerful tool for addressing sauropod paleobiology, with most focus on adult and subadult individuals. The aim of this study is to describe long bone histology (femur) in early juvenile titanosaur sauropods, to expand our knowledge about early stages of development. The material consists of two small femora of indeterminate titanosaurs from the Upper Cretaceous Bajo de la Carpa and Allen formations of Argentina. Both femora from juvenile specimens show predominant fibrolamellar bone tissue with plexiform vascularization pattern, suggesting a fast growth rate. Despite the early stage of development of the studied specimens, secondary remodelling is evident in one of them. In the other sample, a growth mark is observed, which suggests unexpected cyclical growth and a possible departure from the typical growth strategy of sauropod dinosaurs. In addition, we examine indeterminate long bones of titanosaur embryos from the Anacleto Formation of Argentina. The embryos shows poor development of cortical bone, high density of large simple canals and presence of Kastschenko's line suggest that these individuals died during an early stage of ossification. This study reveals that the early growth of at least some titanosaurs departs from the reported in neosauropod dinosaurs.