Embryonic Development and Cranial Ossification Sequence in Two Heremites Species (Squamata: Scincidae)

Although embryological studies of squamates have a long history, most groups in this large clade remain poorly studied. One such group is the family Scincidae, which consists of morphologically and ecologically diverse lizards. In this study, we describe several stages of embryonic development based on cleared and stained specimens of Heremites auratus and Heremites vittatus. Our analysis indicates that the pterygoid and frontal are the first bones to be ossified at stage 34 in the skull of H. auratus. At stage 37, which was examined in both studied species, the ossified bones include the nasal, maxilla, parietal, prefrontal, premaxilla, postorbital, postfrontal, jugal, squamosal, quadrate, vomer, palatine and all mandible bones. In both species, the skull roof is relatively poorly ossified at stage 37. However, in H. auratus, the frontal and parietal bones ossify at their lateral edges at stage 37, while in H. vittatus, the frontal bones begin to ossify towards the midline. This suggests that ossification occurs later in H. auratus compared to H. vittatus, indicating a heterochronic pattern in ossification between these species. Additionally, pigmentation on the dorsal side of the body and scaling, which covered the entire body by stage 37 in H. vittatus, occur earlier compared to H. auratus. Compared to other scincid species, ossification in these lizards begins at a later stage but is completed earlier.