Phylogenetic implications of the morphology of the braincase of caecilian amphibians (Gymnophiona)

Abstract

Caecilian morphology is strongly modified in association with their fossorial mode of life. Currently phylogenetic analyses of characters drawn from the morphology of caecilians lack resolution, as well as complementarity, with results of phylogenetic analyses that employ molecular data. Stemming from the hypothesis derived from the mammal literature that the braincase has the greatest potential (in comparison to other cranial units) to yield phylogenetic information, the braincase and intimately associated stapes of 27 species (23 genera) of extant caecilians were examined using images assembled via microcomputed tomography. Thirty-four new morphological characters pertaining to the braincase and stapes were identified and tested for congruence with previously recognized morphological characters. The results reveal that when added to previous character matrices, characters of the braincase and stapes resolve generic-level relationships in a way that is largely congruent with the results of molecular analyses. Analysis of a combined data set of molecular and morphological data provides a framework for conducting ancestral character state reconstructions, which resulted in the identification of 95 new synapomorphies for various clades and taxa, 27 of which appear to be unique for the taxa that possess them. Together these data demonstrate the utility of the application of characters of the braincase and stapes for resolving phylogenetic relationships for a group whose morphology is largely confounded by functional modifications. In addition this study provides evidence of the utility of the braincase in resolving problematic morphologybased phylogeny outside of Amniota, in an amphibian group.

The Braincase of Eocaecilia micropodia (Lissamphibia, Gymnophiona) and the Origin of Caecilians

“…The character-taxon matrices of Anderson et al [18] and Maddin et al [28] were utilized in the current study, providing broad coverage of both fossil and extant taxa. The matrix of Anderson et al [18] was modified as per Maddin and Anderson [16], with additional amendments made here (see Table S1 in supporting information ).…”

“…As such, the braincase is morphologically constrained by these intrinsic factors and may be less prone to extrinsic influences such as environment and biomechanical adaptations. The braincase of caecilians, although somewhat modified in response to their burrowing habits, retains significant phylogenetic information capable of resolving genus-level relationships [28]. However, how deep within the caecilian lineage this potential of the braincase persists remains unknown.…”

Evolution of Cranial Shape in Caecilians (Amphibia: Gymnophiona)

“…Kupfer et al 2005;Kupfer et al 2006b;Wilkinson et al 2008;Kuehnel and Kupfer 2012;Gomes et al 2013), phylogeny (e.g. Gower et al 2002;San Mauro et al 2004;Roelants et al 2007;Loader et al 2011;Maddin et al 2012b) and ecology (e.g. Oommen et al 2000;Gower et al 2004;Measey et al 2004;Kupfer et al 2006a).…”

A new species of striped Ichthyophis Fitzinger, 1826 <br />(Amphibia: Gymnophiona: Ichthyophiidae) from Myanmar

“…There is a long and continuing tradition of osteological data being used for inferring phylogeny and in higher-level caecilian classification (e.g., Nussbaum 1979;Wilkinson & Nussbaum 1999;Maddin 2012;Wilkinson et al 2011). However, osteology has been little used in lower-level taxonomy, not least because of the limited availability of material that could be prepared.…”