Periosteal bone growth rates in extant ratites (ostriche and emu). Implications for assessing growth in dinosaurs

The first quantitative experimental data on growth dynamics of the primary cortical bone of young ratites demonstrate the following. 1) From hatching to 2 months of age, cortical thickness remains constant, thereby expressing equilibrium between periosteal bone deposition and an endosteal bone resor ption. 2) Radial growth rates of the diaphyseal bone cortex are high (10-40 mu m . day(-1) on average - maximum 80 mu m . day(-1)) in the hindlimb (fe mur, tibiotarsus and tarsometatarsus). Wing bones are smaller and later dev eloped. They have lower rates of radial osteogenesis (2-14 mu m . day(-1)). 3) High growth rates are linked to densely vascularized primary bone belon ging to the reticular or laminar tissue types. Growth rates Call when bone vascular density decreases. These results emphasize the importance of exami ning a large number of skeletal elements in order to build a precise knowle dge of the general relationship between bone growth rate and bone tissue ty pe. They also stress the potential of bone growth rate quantification among extinct tetrapods, including non-avian dinosaurs. (C) 2000 Academie des sc iences/Editions scientifiques et medicales Elsevier SAS.