Chondrogenic and ossification patterns and sequences in White’s skink Liopholis whitii (Scincidae, Reptilia)

Abstract

The prenatal patterns and sequences of chondrogenesis and ossification are described for the skink Liopholis whitii; eight embryos and one adult specimen were examined. Cranial ossification begins in elements of the braincase and the palate, followed by areas of the lower jaw and the cranial roof. Ossification proceeds anteroposteriorly along the axial skeleton and from proximal to distal in the forelimbs and hind limbs. In the zeugopods, the ossification progresses from posterior to anterior, while there is also a strict postaxial order in the autopods with the predominance of digit III in the forelimb and digit IV in the hind limb. Ossification of the femur and tibia starts before the corresponding elements of the forelimb, but simultaneously with the onset in clavicles. Elements of the hind limb display advanced ossification with respect to their forelimb counterparts, with earlier uptake of Alizarin Red in the tarsals, metatarsals and phalanges. The preaxial area of the fused stragalocalcaneum-complex is first to begin ossification among the tarsals. The sequence of ossification is mostly conserved in the skeleton of squamates, as shown in a comparative analysis of heterochrony, but some shifts were found in cranial, vertebral and autopodial regions.