A comparison between phalangeal skeletochronology and cephalic parietal rings in lizards

The well-defined, layered organization of the cephalic scales in many lacertilians could offer a noninvasive alternative for estimating the individual age of these vertebrates. This study aimed to validate the method of age determination based upon the cephalic scale rings in the genus Podarcis, comparing it to phalangeal skeletochronology, a widely used and highly reliable indirect method for estimating the age of ectotherm vertebrates. We analyzed individuals of P. bocagei (n = 48), P. muralis (n = 16) and P. siculus (n = 8). For each individual, we compared the number of cephalic layers with the number of lines of arrested growth (LAGs) observed in the phalanx using the classic skeletochronological technique. Our results showed a common trend between skeletochronological and cephalic rings-based age estimates across the three species, but with low correspondence (37.5%, 37.5%, and 27.2% in P. muralis, P. siculus, and P. bocagei, respectively). As expected, body size increased nonlinearly with both age estimate methods. However, Spearman’s correlation and model 2 linear regression suggest limited precision and bias when transposing results between different methods. Overall, the cephalic rings method faced practical challenges for lacertid species in the genus Podarcis. We advise against mixing age estimates obtained through different methods due to these inconsistencies.