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Background Age estimation in vertebrates has always been a tricky and dubious procedure. The method of skeletochronology is commonly used for age estimation in poikilothermic and in some homoiothermic animals. This method is based on counting arrested growth lines (LAGs) within bone structures (tubule bones or teeth) in modern living or fossil animals. However, it fails to reveal the age with necessary precision due to hibernation and aestivation periods, hence, some referent method of age estimation is required for evaluating better precision. During the previous studies of population age structure in several species of rock lizards (Darevskia) we prepared microscope slides of finger bones and noticed presence of well-distinguished cornified unguis lamellas of the finger claws. We put forward that the number of these lamellas coincides with the number of LAGs in the periosteum bone of the same finger. To test this hypothesis, we performed special study and compared number of LAGs within each finger bone and cornified claw using traditional skeletochronological technique. Results The conducted analysis revealed positive correlation (rs=0.933, p < 0.001) and no significant differences between the number of LAGs in the bone and unguis lamellas of the same fingers of three species of Palearctic rock lizards (Darevskia portschinskii, D. raddei, D. valentini). We found no distinguished cornified lamellas in the claw of the tropical skink Sphenomoprhus maculatus. Conclusion We assume that the proposed method may be an efficient and reliable means of ecological studies based on toe-clipping and vital age estimation in lizards and, possibly, other poikilothermic vertebrates, as a double-check method based on two independent registration structures present potentially preventing possible mistakes in age estimation.