Ontogenetic changes in the histological features of zonal bone tissue of ruminants: A quantitative approach

Bone histology is a powerful tool to explore the growth patterns of vertebrates. There is a broad consensus that a deeper understanding of bone development in living taxa is still lacking. Here, we aim to explore the ontogeny of the fibrolamellar (FLC) zonal bone of mammals by studying histological sections of the femoral growth series of 84 wild ruminants. Our results indicate that large ruminants do not preserve a complete ontogenetic record of primary bone growth, so it is necessary to use methods of age retrocalculation. Our study also stresses the ontogenetic variation in histological features of the FLC-zonal bone (vascular orientation, vascular and osteocyte lacunae density) that may reflect the slowdown in growth associated with the onset of physiological maturity. We conclude that the transition from FLC bone to lamellar bone (EFS) in ruminants records the fundamental life history trade-off between growth and reproduction (reproductive maturity).