Relationship between bone growth rate and the thickness of calcified cartilage in the long bones of the Galloanserae (Aves)

The histological features of mineralized tissues can be preserved for hundreds of millions of years, and are therefore important potential sources of information for reconstructing the life history traits of extinct species. Bone growth rates and the duration of the growth period have recently been estimated in fossil archosaurs from periosteal ossification (a mechanism responsible for bone diametral growth). Similarly, data on endochondral ossification (the mechanism responsible for bone longitudinal growth) may also yield information on growth duration and rate among extinct vertebrates, as long as potentially informative structures are preserved. However, in order to carry out palaeobiological estimations of growth rate and/or the duration of growth, it is first necessary to quantify in extant species the relationship between these life history traits and the histological features of endochondral ossification that are potentially preserved in the fossil record. Here we analyse the ontogenetic variation of both bone longitudinal growth rate and the thickness of the calcified cartilage in the femora of two Galloanserae (Aves) and find a significant positive relationship between these variables in both species. We discuss possible factors underlying interspecific differences in this relationship, and conclude that it could be applied with caution to draw palaeobiological inferences.