Phylogenetic implications of the morphology and development of the braincase of caecilian amphibians (gymnophiona)
Date
2011
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Abstract
Caecilians, one of the three living groups that comprise Lissamphibia (frogs, salamanders, and caecilians ), are considered the least well understood for many aspects of their biology. The current study set out to develop a framework, within which aspects such as morphology and evolution could be explored, by attempting to resolve the poorly understood phylogeny of caecilians by examining the morphology of the braincase and stapes. The braincases and stapedes of twenty-seven species of caecilian were examined using micro-computed tomography and histologically-prepared specimens. The braincases were first examined for their potential to yield phylogenetic information by deciphering variation in the antotic region. Deriving from assessments of homology based on transmitted structures, eight different patterns of antotic foramina are identified and the distribution of these patterns is congruent with hypotheses of relationships based on molecular data. It is demonstrated that heterochrony was likely a driver of morphological variation; however, causes of such modifications failed to be correlated with the patterns observed. Description of the entire braincase and stapes permitted the identification of thirty-two new morphological characters. These characters are shown to be sufficient for resolving genus-level relationships in the context of previously developed matrices, in a way that is congruent with hypotheses based on molecular data. A combined phylogenetic analysis of morphological and molecular data provides a test of congruence between morphological characters in a total evidence context, permitting ancestral character state reconstructions to be conducted and the plesiomorphic condition of the braincase and stapes of Gymnophiona to be inferred. The ability for the braincase to reveal phylogenetic information in the broader context of lissamphibian phylogeny was explored by considering the auditory apparatus. New observations, combined with those made previously, are used to infer the presence of the lissamphibian-type ear in caecilians, suggesting the secondary loss of the tympanic and opercularis hearing pathways in caecilians. The evolution of the lissamphibian-type ear is most parsimoniously explained under the rnonophyletic ternnospondyl hypothesis of lissamphibian phylogeny. The data presented here, and the new phylogenetic framework incorporating morphology, provide a means to further explore evolution in a group with diverse factors influencing the evolution of morphology.
Description
Bibliography: p. 449-479
A few pages are in colour.
A few pages are in colour.
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Citation
Maddin, H. C. (2011). Phylogenetic implications of the morphology and development of the braincase of caecilian amphibians (gymnophiona) (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/4337