Estimation and rapid identification of later stages during embryonic development of the oviparous lizard Sceloporus aeneus (Squamata: Phrynosomatidae).

Stages of embryonic development for reptiles have been presented in tables that may include all or part of embryonic development. When oviposition occurs in some lizards, embryos are already in the later stages of development; likewise, the size of the eggs increases as incubation time progresses. However, it is unclear whether there is a relationship between the size of the egg and embryo development. Therefore, the objective of this study was to define whether there is a correlation between the size and volume of eggs and the embryonic stage of the lizard Sceloporus aeneus (Squamata: Phrynosomatidae). This study described the most relevant morphological changes in embryogenesis, from the moment of oviposition until shortly before hatching. Our results showed a statistically significant correlation between the stage of embryo development and the size and volume of eggs. Eleven development stages were characterized, initiating at the moment eggs were laid. Each developmental stage was mainly identified according to the morphological characteristics of the limbs and the body pigmentation. Our study links the growth of eggs with the developmental stage of embryos, which can provide a useful tool to those studies that require specific stages of the embryos and in those that undertake analysis of biological processes, such as organogenesis. The S. aeneus lizard manifests similar morphological and skeletal limb development to that documented for other species. Thus, analysis of limbs represents a quick and easy way to establish stages of embryonic development in S. aeneus, allowing us to compare their development with other species.