Les marques de croissance osseuse comme indicateurs de l‘âge chez les lézards

From a comparative viewpoint, this paper deals with structural and functional aspects of skeletal annulations in lizards, especially those displayed by sections cut transversally through the larger bones of the appendages. Cross‐sections of the diaphyses exhibit an alternation of concentrically arranged thinner and thicker annulations which were formed during colder and warmer seasons, respectively. The thinner annulations are chromophile and anisotropic but not hypermineralized; they are generally referred to as “resting lines” or “adhesion lines” and are due to a slowing down of the temperature‐dependent growth process; they also differ structurally from “cementing reversal lines”. In certain cases, the thinner annulations (here called LAC) are surrounded by bone lamellae and thus compare closely with the annuli on the flat bones. From the study of two lizards of known age, as well as on the basis of a preliminary experimentation with fluorochrom labelling, it has been demonstrated conclusively that the recurrence of the LAC in lacertilians shows an annual regularity. Therefore, it would seem that the LAC can be employed for age determination in lizards.