3/24/2023 0 Comments Carl tabulo![]() ![]() fragilis retains a paedomorphic state of the nasal region. fragilis differs considerably in the composition of the orbitotemporal region. apodus shows a strikingly similar development of this region to other squamates. Among others, the most important differences are in the orbitotemporal region. Anguid lizards represent a unique group of squamates, which contains limbed and limbless forms and show conspicuous variation of the adult skull.īased on several embryonic stages of the limbless lizards Pseudopus apodus and Anguis fragilis, and by comparing with other squamates, we identified and interpreted major differences in chondrocranial anatomy. Squamates are particularly important in this regard as they maintain at least part of the chondrocranium throughout their whole ontogeny until adulthood. In vertebrates, the skull evolves from a complex network of dermal bones and cartilage – the latter forming the pharyngeal apparatus and the chondrocranium. However, the results of the analyses of the larger dataset support Testudines as sister to all of Diapsida. The results of the analyses of the smaller dataset do not support any particular placement of turtles over another. Endochondral bones were not found to shift any more often than dermal bones during the course of evolution. With the data used in this study, I was also able to empirically assess the hypothesis that endochondral bones shift more often during evolution than dermal bones. Each analysis had three iterations for the three supported placements of Testudines within Amniota. A larger dataset with missing data was also analyzed by PGi. A smaller, complete dataset was analyzed by Continuous Analysis and PGi so that a direct comparison of the methods could be made. In addition to the use of Continuous Analysis (Germain and Laurin 2009), this study recorded the internodal heterochronies reconstructed with this method. This study specifically addressed temporal bone heterochony among amniotes using the methods of Continuous Analysis (Germain and Laurin 2009) and Parsimov-based Genetic Inference (Harrison and Larsson 2008) to analyze cranial ossification sequences from representative taxa of all major orders of amniotes. If turtles are descended from diapsids, as molecular data suggests, this implies a rapid transformation of the temporal region from the diapsid condition to the anapsid condition. Among other unique morphological adaptations, turtles possess an anapsid (unfenestrated) condition of the temporal region of the skull. The study of developmental systems may help to resolve the disagreement between morphological data and molecular data when it comes to the placement of Testudines among Amniota. Some reproductive data obtained during the collection of data could be compared with those from the literature. The remnants of pectoral and pelvic girdles are represented by cartilaginous rods. The number of vertebrae is fixed from the beginning of their differentiation. The vertebral column shows an antero-posterior gradient of vertebral differentiation. The compound mandibular bone arises from the ossification of the posterior part of Meckel's cartilage and the fusion of at least two dermal centers, interpreted as surangular and splenial. The lateral element-X does not ossify until very late in embryogenesis and is interpreted as an epiphysial ossification. 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 tabulosphenoid forms from two cartilages to which are added extensive membranous ossifications. In contrast to the condition in other squamates, the premaxilla seems to arise azygously from the beginning or to represent very early fusion during embryogenesis. The external characterization of embryos serves as an incomplete developmental table. An assemblage of amphisbaenian embryos has allowed us to characterize the external morphology of the developing embryos as well as the chondrification and ossification sequences of their skeletal elements. ![]()
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