Morphological study of the supratrochlear foramen in <i>Canis lupus</i> ssp.

The domestic dog (Canis lupus familiaris), a species characterized by remarkable phenotypic diversity resulting from selective breeding, is among the several mammals that may exhibit an anatomical perforation of the humeral condyle, designated as the supratrochlear foramen (STF). The prevalence of the STF varies considerably across mammalian species and has been proposed to reflect functional adaptations linked to evolutionary and biomechanical factors, particularly in the human humerus. To the best of our knowledge, comprehensive studies on STF variation within present-day canine populations remain scarce. This study aimed to determine the prevalence and morphology of the STF in extant dogs, and to compare these findings with those from Roman Imperial Period dogs, and Iberian wolves (Canis lupus signatus), a subspecies considered representative of the dog's wild ancestor, in order to explore evolutionary changes within Canis lupus subspecies. We analyzed 269 humeri (123 extant dogs, 76 ancient dogs, 70 Iberian wolves) using osteometric measurements and statistical analysis. Our results demonstrate that the STF was observed in 73.17% of extant dogs, compared to 82.89% in ancient dogs and 98.57% in Iberian wolves, suggesting a reduction in its prevalence over time in domestic lineages that may be linked to human-driven selection processes. In all studied groups, the STF was consistently located closer to the lateral humeral epicondyle, and its predominantly transversely elongated shape reveals a common morphological pattern across Canis lupus subspecies. Despite differences in humeral size among groups, STF dimensions showed a positive correlation with overall humeral measurements, with larger humeri exhibiting proportionally larger and more frequent STFs. Extant dogs displayed the smallest STF dimensions, followed by ancient dogs, with Iberian wolves having the largest. Considering the potential impact of the STF on the biomechanical properties of the distal humerus, this study provides new insights into its anatomical variability in dogs, emphasizing its clinical relevance for orthopedic diagnostic accuracy and surgical treatments in veterinary medicine.