Intraspecific sternal variation in Neophocaena asiaeorientalis across sex and age groups by PMCT 3DVRI

Narrow-ridged finless porpoise (NRFP) ( Neophocaena asiaeorientalis ) is an endangered species in which age and sex estimations are challenging in decomposed or incomplete stranded specimens. This study examined the sternum as an alternative landmark using three-dimensional volume-rendered imaging (3DVRI) derived from post-mortem computed tomography (PMCT) data. Eighty-nine stranded NRFP specimens (50 females and 39 males) from the waters of Korea (2019-2025) were analyzed. Sixteen morphometric measurements were evaluated for sexual dimorphism and age-related morphometrics. Three parameters showed significant sexual dimorphism differences ( p < 0.05), and significant age-related morphometrics differences were found in four and fourteen parameters in females and all specimens respectively ( p < 0.05). Four morphological types were identified, with a shifting of types from non-adults to late adults of both sexes being observed. The findings suggest that the sternum may aid in approximate age classification in stranded NRFP specimens.