Ontogeny of the skull, lower jaw, and hyobranchial skeleton of Hypogeophis rostratus (Amphibia: Gymnophiona: Caeciliidae) revisited.
Few detailed descriptions of the development of the head skeleton in caecilian amphibians are available. One of those is the work of Marcus and students (e.g., Gehwolf [1923] Z Anat Entwick 68:433-454; Marcus [1933] Anat Anz 80:142-146; Marcus et al. [1935] Gegenbaurs Morphol Jb 76:375-420) on the morphology and development of the skull, lower jaw, and hyobranchial skeleton in the Seychellean caeciliids Hypogeophis rostratus and Grandisonia alternans. These workers described a high number of individual ossifications that fuse during ontogeny to form the adult skull. Although later studies have doubted the generality of those observations, the work of Marcus and his students has been hugely influential in subsequent studies of caecilian skull morphology and amphibian evolution. Based on new observations on an ontogenetic series of 32 sectioned and cleared and stained specimens, ranging from the beginning of chondrification to the adult, the development of the skull, lower jaw, and hyobranchial skeleton of H. rostratus are described. The new results are largely incompatible with those of Marcus and students and no evidence for several of the reported ossifications, including supra-, infra-, and basioccipital, epiotic, pleurosphenoid, preethmoid, posterior vomer, prepalatine, quadratojugal, postparietal, second coronoid, supraangular, and complementare, is found. It is argued that most of Marcus et al.'s reports of nonexistent ossifications are based on false phylogenetic preconception, misinterpretation of the observed morphology, and technical error. Data on the ossification sequence of the skull and lower jaw in H. rostratus are provided and briefly compared to published information on Dermophis mexicanus and Gegeneophis ramaswamii.
Müller
Hendrik
H
Department of Zoology, The Natural History Museum, London, UK. henm@nhm.ac.uk
D000663:Amphibians / Q000033:anatomy & histology / Q000196:embryology*; D000818:Animals; D001934:Branchial Region / Q000033:anatomy & histology / Q000196:embryology* / Q000648:ultrastructure; D008334:Mandible / Q000033:anatomy & histology / Q000196:embryology* / Q000648:ultrastructure; D012886:Skull / Q000033:anatomy & histology / Q000196:embryology / Q000648:ultrastructure