Osteology of Calluella guttulata (Blyth 1855) and Associated Commentary on Evolution in the Family Microhylidae (Anura)

Abstract

Microhylid osteology is a morass of unusual structures and repetitive convergent evolution. The available phylogenetic information is limited, and the osteological information barely scratches the surface of the diversity present in the group, but even this much is enough to begin to identify certain patterns and areas of interest. Microhylinae, and to a lesser extent Gastrophryninae, in particular show high degrees of convergence both in pectoral and vomerine structure compared to Cophylinae and Asterophryinae. It remains to be seen whether other variable osteological structures, such as hyobranchial apparatuses or carpal arrangement, also show this level of convergence within these groups. Further taxonomic sampling is of utmost importance, both for osteology and phylogeny, as the few osteological descriptions available do not always correspond with the species used in existing phylogenies. Higher phylogenetic resolution could clarify many situations where the occurrence or number of occurrences of convergence is currently unclear. Further sampling, too, will inevitably shed light on the functional significance of many microhylid traits. The hyobranchial apparatus, for example, is clearly a uniquely modified feature of the Microhylidae, but almost nothing is known about corresponding changes in the morphology of the attached muscles, and only a few examples of hyobranchial diversity have even been described. There are several possible avenues of study here where unique microhylid osteology might indicate a particularly unique functionality, all wide open to possible future research.