Skeletal development of the direct-developing caecilian Gegeneophis ramaswamii (Amphibia: Gymnophiona: Caeciliidae)

Abstract

A few previous studies of skeletal and especially skull development in Gymnophiona often provided contradictory results. We studied the development of the skull and vertebral column of Gegeneophis ramaswamii, a direct-developing Indian caeciliid, based on 13 specimens. The chondrocranium forms at (Brauer in Zool Jahrb Anat 12:477-508,1899) stage 38. First dermal and perichondral ossifications occur at stage 40. The first dermal bones to form are the mentomeckelian, dentary, angular, vomer, and premaxillary. These are followed by the coronoid, palatine, pterygoid, maxillary, and the skull-roofing bones. The last occurring dermal ossifications are the parasphenoid and the squamosal. We present evidence for the occurrence of a lacrimal bone. No ectopterygoid, basioccipital, supraoccipital, pleurosphenoid, postorbital, or supratemporal elements were found. We assess the homology of the bones constituting the caecilian skull and discuss the above-mentioned terminologies. The phylogenetic implications of our findings are briefly discussed and we conclude that the evidence from developmental morphology is at present consistent with a monophyletic Lissamphibia of temnospondyl origin.

Focal Review: The Origin(s) of Modern Amphibians

“…However, Müller and colleagues have shown that in several instances these statements prove unfounded. For example, earlier statements that the caecilian stapes is a composite bone, the footplate being derived from the otic capsule wall and thus homologized with the operculum of frogs and salamanders, are unfounded in their developmental series, which shows the stapes to form from a single ossification only, and begins with a suspensorial support role as in some salamanders (Müller et al 2005). On the other hand, they found support for the presence of a lacrimal bone, based in part on corresponding articulations with the highly modified nasolacrimal duct portion of the tentacular organ.…”

“…Such work is now underway. Müller and colleagues (Müller et al 2005;Müller 2006) have been publishing a number of careful descriptions of the pattern of ossification of caecilian skulls that have been very insightful. Because of the highly coossified skulls of caecilians, a lot of previous work (i.e., Marcus et al 1935) focused on finding early centers of ossification, and then making homology statements for those centers, and thus potential comparisons with archaic amphibians with multiple cranial bones.…”

Cranial musculature in the larva of the caecilian, Ichthyophis kohtaoensis (Lissamphibia: Gymnophiona)

“…Wake and Hanken (1982) studied the development of the cranium in fetuses of the viviparous Dermophis mexicanus. Details of the larval hyobranchial apparatus are known for Hypogeophis rostratus (Gehwolf, 1923;Mü ller, 2006), Grandisonia alternans (Gehwolf, 1923), Gegeneophis ramaswamii (Mü ller et al, 2005), Ichthyophis glutinosus and I. monochrous (Visser, 1963), Epicrionops bicolor and E. petersi (Wake, 1989) and for fetal stages of the viviparous species Dermophis mexicanus (Wake, 2003).…”

“…The larval skull morphology was described for Ichthyophis glutinosus (Peter, 1898;Visser, 1963), I. monochrous (Visser, 1963), Gegeneophis carnosus (Ramaswami, 1948), G. ramaswamii (Mü ller et al, 2005), Hypogeophis rostratus (Marcus et al, 1935;Mü ller, 2006), and Grandisonia alternans (Marcus et al, 1935). Early stages of the viviparous Typhlonectes compressicauda were described by Wake et al (1985).…”

Embryonic Staging Table for a Direct‐Developing Salamander, Plethodon cinereus (Plethodontidae)

“…This life history strategy has evolved independently in several amphibian lineages (Hanken, 1999), providing an opportunity to compare embryological features that correlate with direct-development between multiple clades of living amphibians (e.g., Blackburn, 2004;Mü ller et al, 2005;Kerney et al, 2007). Plethodontids are the only salamander family known to contain direct-developing species.…”