Unravelling the difference in craniofacial morphology of Yucatan miniature and standard pigs during postnatal ontogeny.

The Yucatan miniature pig has become a preferred model for craniofacial research due to its anatomical and physiological similarities to humans. However, the factors driving midfacial hypoplasia in Yucatans during postnatal ontogeny remain unclear. This study characterized postnatal skull growth and development, and morphological variations in Yucatan and standard (domestic) pigs, with a focus on the role of joint maturation in resulting craniofacial dysmorphology. Forty available head specimens (Yucatan: n = 20, 0-12 months; standard: n = 20, 0-8 months) were analysed using multidimensional craniometric measurements and geometric morphometrics. Results show that both breeds follow an allometric growth trajectory, largely driven by the expansion of craniofacial organs and capsules. At birth, skull morphology was similar between breeds; however, Yucatans developed a shorter face and more compact neurocranium, while maintaining a nearly identical mandibular shape to standard pigs. Over the first three months, Yucatans exhibit delayed calvarial suture fusion compared with standard pigs, while skull base synchondroses remain patent in both breeds. These findings reflect the scaling relations between breeds and highlight differential growth patterns of the midface, neurocranium and mandible in Yucatans, emphasizing their interactions with organ development, cavity expansion and joint maturation, offering insights into the mechanisms driving craniofacial diversification in pig models.