Bone lamina thickness,bone apposition rates,and age estimates in sauropod humeri and femora

Laminar fibrolamellär bone from the mid-shaft region of sauropod humeri and femora was analyzed quantitatively to understand Variation in lamina thickness and apposition rate. The samples were derived from five taxa (Apatosaurus, Barosaurus, an indeterminate gracile diplodocid,Brachiosaurus, Janenschia) and two localities (Tendaguru beds, Tanzania, and Howe-Stephens Quarry, Morrison Formation, Wyoming, USA). Lamina thickness is rather constant at 4–6 laminae/mm (mean 4.8), independent of locality, taxon, bone, and ontogenetic age, suggesting structural constraints as a cause. Bone apposition rate was calculated in bones with annual growth lines (polish lines) by two methods to serve in age estimates of individuals without growth lines and unsampled individuals. Apposition rates are rather variable (1–20 (jm/day), resulting in a wide bracket for the ages estimated. Our age estimates are compatible with recent estimates derived by other methods, however.