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Age pbkp_rediction model for adult male Galapagos sea lions based on skull measures

Abstract:

The age of adult mammals is required for studies related to ontogeny patterns, growth rate, and life history. However, the reliable age determination from skulls with no canine teeth is generally inaccurate. This research aims to develop an age pbkp_rediction model for adult male sea lions by measures of a particular skull section, which was validated by counting dentine growth layers in their upper canine teeth. We used skulls and teeth of 49 Galapagos sea lions (GSL, Zalophus wollebaeki) aged between 13 and 20 years old collected in different breeding rookeries of the Galapagos archipelago between 2000 and 2018. Two groups of skull measures were considered: (1) measures correlating with total skull length and (2) measures used in growth models in the literature. A generalized additive model was adjusted to estimate ages on skulls. The measures that best described the age pbkp_rediction model were maxillary tooth row length (MTRL), occipital plate height (OPH), anterior nasal width (ANW), braincase posterior width (BPW), braincase width (BW), jugal supraorbital process height (JSPH), nasal length (NL), orbital length (OL), and postpalate length (PosL) (r2 = 0.93; AIC = 56.16). The pbkp_redicted ages were close to those counted in teeth with a standard deviation between 0.10 and 0.45 of the average age. This validates the usefulness of our approach to determine age in skulls of GSL even with missing teeth. We recommend the assessment and application of this methodology in morphometric research of pinnipeds but considering morphological characteristics and the skull development of each species.