Phylogenetic relationships, higher classification, and historical biogeography of the microhyloid frogs (Lissamphibia: Anura: Brevicipitidae and Microhylidae).

One-hundred and five microhylid species, which represent 56 genera in all ten subfamilies, were examined for external morphology, myology, and osteology in order to determine the phylogenetic relationships among these species and between microhylids and other frog families. Phylogenetic relationships were analyzed using cladistic methodology, and 28 outgroup taxa, which represent ten frog families, were used to root the hypothesis. Variation is reported in many morphological characters that had been considered constant among microhyloid frogs. New morphological characters that are useful in microhylid systematics are described and discussed. One-hundred-twenty equally parsimonious cladograms, each with a consistency index of 0.089, are found using 133 taxa and 188 characters. The low consistency index of the phylogenetic hypothesis proposed in this study reflects the high levels of convergences and reversals of morphological characters in microhylid evolution. More than two thirds of the characters show character state reversals. This suggests that reversal is more important in microhylid evolution than convergence. Such plasticity of morphological character evolution in microhylids can probably be attributed to heterochrony, as indicated by the short or absent larval stage found in many microhylids. The microhyloid phylogeny proposed in this study also offers an explanation for the origin of scoptanuran tadpoles through neoteny. The monophyletic Microhyloidea delimited in this study includes two monophyletic taxa: Brevicipitidae and Microhylidae. Hemisus and Rhinophrynus form a clade that is the sister taxon of brevicipitines in Brevicipitidae. Within Microhylidae, only two subfamilies are now recognized: Cophylinae and Microhylinae. The most parsimonious explanation for the distribution of monophyletic microhylid lineages in South America, Madagascar, and Southeast Asia is through vicariance. Microhyloids are hypothesized to have existed in Gondwanaland before its breakup prior to or during the early Jurassic. This study shows that the topology of the cladogram and the nature of the synapomorphies of microhyloid taxa can be affected by the choice of outgroup as well as ingroup taxa employed. In order to minimize the assumptions that are associated with cladistic analyses, selection of outgroup taxa should not be bounded by the present classification, because doing so emphasizes stability rather than phylogenetic precision.Ph.D.Biological SciencesMorphologyZoologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/129503/2/9513512.pd