Mapping the growing skeleton: Macroscopic analysis of the extracortical topography of long bones in early human development

External surfaces of developing long bones exhibit complex morphological patterns that reflect coordinated processes of vascular invasion, periosteal apposition, and structural remodeling. Despite their interpretative importance, systematic baseline descriptions of extracortical topography during early ontogeny remain scarce, hampering differentiation between normal developmental variation, pathological alterations, and taphonomic changes. This study provides the first comprehensive macro- and microscopic characterization of surface features in fetal, infant, and child long bones using an identified skeletal collection. A total of 172 individuals aged between five gestational months and six postnatal years from the Granada osteological collection were examined under magnification and photographed to document age-related variation in physiological bone formation patterns, porosity morphology, and cortical compaction across, clavicles, humeri, radii, ulnae, femora, and tibiae. All elements displayed a consistent developmental trajectory: intense surface activity throughout the fetal period and early infancy, transitioning to progressive consolidation during the first year. Vascular channels penetrate perpendicular to cortical surfaces at mid-diaphysis, shifting to oblique trajectories when approaching metaphyseal regions. Surface morphology varies spatially within individual bones: areas experiencing substantial mechanical stress from muscular and fascial attachments retain elevated porosity and perpendicular bone spicules longer than less-loaded mid-shaft segments. Timing and extent of cortical maturation differ among skeletal elements according to their functional demands, with lower limb bones achieving structural stability earlier than upper limb counterparts. This morphological framework provides anthropologists with original anatomical information and diagnostic criteria to distinguish developmental processes from pathological or post-depositional modifications, improving interpretative accuracy in bioarchaeological and forensic investigation of immature remains.