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 prediction 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 prediction 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 predicted 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.

与个体发育模式，生长速率和生活史相关的研究需要成年哺乳动物的年龄。但是，从没有犬齿的头骨可靠地确定年龄通常是不准确的。这项研究的目的是通过测量特定头骨部分的尺寸来开发成年雄海狮的年龄预测模型，该模型通过对上犬齿中牙本质生长层的计数进行验证。我们使用了49只加拉帕戈斯海狮（GSL，Zalophus wollebaeki）年龄介于13岁至20岁之间的动物，收集于2000年至2018年之间的加拉帕戈斯群岛不同繁殖群中。考虑了两组颅骨测量值：（1）与颅骨总长相关的测量值；（2）在生长模型中使用的测量值文学。调整了通用的加性模型以估计头骨的年龄。最能描述年龄预测模型的措施是上颌牙排长度（MTRL），枕骨板高度（OPH），鼻前宽度（ANW），脑箱后宽度（BPW），脑箱宽度（BW），眶上法高度（ JSPH），鼻长度（NL），眼眶长度（OL）和后pal长度（PosL）（r ² = 0.93; AIC = 56.16）。预测年龄接近牙齿计数的年龄，标准偏差为平均年龄的0.10至0.45。这证实了我们确定牙齿缺失的GSL头骨年龄的方法的有用性。我们建议将这种方法的评估和应用在针尖形态研究中，但要考虑每个物种的形态特征和头骨发育。