Embryonic development of the skeleton of Amphisbaena darwini heterozonata (Squamata : Amphisbaenidae)

An assemblage of amphisbaenian embryos has allowed us to characterize the e xternal morphology of the developing embryos as well as the chondrification and ossification sequences of their skeletal elements. The external charac terization of embryos serves as an incomplete developmental table. In contr ast to the condition in other squamates, the premaxilla seems to arise azyg ously from the beginning or to represent very early fusion during embryogen esis. The tabulosphenoid forms from two cartilages to which are added exten sive membranous ossifications. The two parietals engage in medial fusion at the midline, where the anterior process of the synotic tectum ossifies and forms the sagittal crest. The lateral element-X does not ossify until very late in embryogenesis and is interpreted as an epiphysial ossification. Th e compound mandibular bone arises from the ossification of the posterior pa rt of Meckel's cartilage and the fusion of at least two dermal centers, int erpreted as surangular and splenial. The vertebral column shows an antero-p osterior gradient of vertebral differentiation. The number of vertebrae is fixed from the beginning of their differentiation. The remnants of pectoral and pelvic girdles are represented by cartilaginous rods. Some reproductiv e data obtained during the collection of data could be compared with those from the literature. (C) 1999 Wiley-Liss, Inc.