We redescribe the type material of Phyllodactylus siamensis Boulenger, 1899, type species of the Southeast Asian gekkonid genus Dixonius Bauer, Good & Branch, 1997, using external morphology and cranial osteology (by Micro-Computed Tomography, µ-CT). There is some evidence that the type series contains more than one species; we hence designate a lectotype in order to stabilize nomenclature and provide more precision on the geographical location of the type locality. Because the current concept of Dixonius siamensis auctorum is incomplete and composite, we provide a revised diagnosis based on the presently designated lectotype and a paralectotype from the same locality, as well as observations on new material from the type locality and the first photographs of live topotypical individuals. We regard Dixonius siamensis as probably geographically restricted to the Dong Phaya Yen mountain range in central Thailand, and the numerous published mentions of this species from outside this range likely refer to other or undescribed taxa. We treat Phyllodactylus burmanicus Annandale, 1905 from Tavoy, southern Myanmar, as a valid species, as Dixonius burmanicus comb. nov.
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RBINS Staff Publications 2024
Abstract Caecilians are elongate, limbless and annulated amphibians that, as far as is known, all have an at least partly fossorial lifestyle. It has been suggested that elongate limbless vertebrates show little morphological differentiation throughout the postcranial skeleton. However, relatively few studies have explored the axial skeleton in limbless tetrapods. In this study, we used ?CT data and three-dimensional geometric morphometrics to explore regional differences in vertebral shape across a broad range of caecilian species. Our results highlight substantial differences in vertebral shape along the axial skeleton, with anterior vertebrae being short and bulky, whereas posterior vertebrae are more elongated. This study shows that despite being limbless, elongate tetrapods such as caecilians still show regional heterogeneity in the shape of individual vertebrae along the vertebral column. Further studies are needed, however, to understand the possible causes and functional consequences of the observed variation in vertebral shape in caecilians.
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RBINS Staff Publications 2022
