Bone surface texture as an ontogenetic indicator in long bones of the Canada goose Branta canadensis (Anseriformes: Anatidae)

Growth series of femora, tibiotarsi, and humeri of the Canada goose Branta canadensis were examined to evaluate whether bone surface textures are reliable indicators of relative age and skeletal maturity in this taxon. The relationship between surface texture and skeletal maturity was analysed by comparing element texture types with both size-based and size-independent maturity estimates. A subsample of hindlimb elements was thin sectioned to observe histological structures underlying various surface textures. Three relative age classes of elements are identifiable based on surface texture. Juvenile and subadult bone textures have fibrous and/or porous areas on the bone shaft and are distinguished by the presence (in juveniles) or absence (in subadults) of coarse longitudinal striations in proximal and/or distal regions. Adult bone texture lacks surface porosity. Immature textures are caused by channels in fibrolamellar bone intersecting the bone surface; the presence or absence of striations is determined by channel orientation. Mature textures may be underlain by fibrolamellar bone with little to no surface exposure of channels, or by lamellar bone deposited after rapid growth ceases. The utility of the textural ageing method appears intimately related to the uninterrupted determinate growth regime of Branta. This suggests that bone surface textures may prove useful as skeletal maturity indicators in both modern and fossil taxa with similar growth regimes, but may not necessarily be reliable for taxa with interrupted and/or indeterminate growth.