Osteometric Morphological Study of Cervical Vertebrae and Apparent Sex-based Trends in Tripureswari Ducks of Tripura, India

Abstract

Background: The cervical skeleton provides the structural basis for avian neck mobility and extreme flexibility, compensating for the immobility of the eyes. However, the cervical osteology of the indigenous Tripureswari duck, a distinct breed from Tripura in north-eastern India, has not been described. Objective: To document the number, size and proportions of cervical vertebrae in adult Tripureswari ducks and to examine patterns in linear measurements and ratios of typical cervical vertebrae in relation to sex, where present. Methods: Head and neck specimens from four adult males and four adult females (eight birds in total), collected from a slaughterhouse, were macerated and examined. Five linear measurements were recorded for each vertebra: vertebral height (VH), zygapophyseal width (ZW), centrum width (CW), centrum height (CH) and centrum length (CL). Ratios were derived from these measurements. The surface areas of the typical cervical vertebra (C10), including the butterfly-shaped dorsal, shield-shaped ventral, H-shaped articular and saddle-shaped articular surfaces, were estimated from photographs using ImageJ. Data are expressed as mean ± standard error. Results: The craniocaudal patterns of cervical vertebral measurements were broadly similar in both sexes of Tripureswari ducks. Fourteen cervical vertebrae were identified. ZW and CW generally increased caudally; CH decreased to a minimum at C8 and subsequently increased in a stepwise manner; CL peaked at C8–C9, apart from the axis; and VH showed peaks at C3 and C12. Mean measurements were generally greater in males than in females: CH (+10.7%), CL (+7.6%), ZW (+6.1%), CW (+6.1%) and VH (+3.3%), with exceptions at individual vertebral levels (including CW at C14). CH and CL were greater in males at all 14 vertebral levels. Males had a higher CH/CW ratio (0.984 ± 0.006 versus 0.946 ± 0.009) and a lower VH/CL ratio (0.760 ± 0.005 versus 0.788 ± 0.005). At C10, dorsal and ventral surface areas were greater in males, whereas saddle-shaped articular surface areas were comparable between sexes. Conclusion: The cervical osteometric profile of the Tripureswari duck broadly follows the cranial, middle and caudal organisation described in birds. Apparent sex-related trends were observed in centrum length and height and in the large non-articular surfaces, whereas the articular saddle area was comparatively similar. Given the small sample (n = 8), these findings should be regarded as preliminary baseline observations rather than statistically validated sex differences.