The three-front model: a developmental explanation of long bone diaphyseal histology of Sauropoda

The bone histology of non-avian dinosaurs is enlightening for understanding many aspects of the growth and development of these long-extinct animals. The rate of bone apposition and remodelling in the shaft of long bones appears to be accelerated in some groups and decelerated in others. We propose a developmental model to illustrate these fundamental aspects of long bone diaphyseal histology at different growth stages. We developed the model based on an ontogenetic series of long bones of the sauropod dinosaur Apatosaurus. The model describes the histology and microanatomy based on three fronts that move radially: the apposition front, the Haversian substitution front, and the resorption front. When applied to additional sauropod dinosaurs, differences and similarities observed in the microstructure of the different taxa could be explained with the model. The benefit of this model is that it is not limited to Sauropoda but appears to be applicable to a broad range of terrestrial amniote long bones and thus could provide unique insights into life history and evolutionary patterns of bone development. (C) 2014 The Linnean Society of London.