Osseous skull development of Ambystoma macrodactylum krausei from post-hatching through metamorphosis

Abstract

Salamander developmental morphological data contribute to deciphering evolutionary relationships of modern/fossil amphibians. This study examines the osseous skull morphology of Ambystoma macrodactylum krausei, from post-hatching through metamorphosis using μCT and synchrotron scanning methods. Skull elements and overall skull shape were described through ontogeny (including one adult). Landmark-based principal components analyses examined shape trends across collection years, premetamorphosis (PM) and metamorphosis (M), and scanning methods. Covariance matrices were compared across collection years. Modularity hypotheses were tested. A. m. krausei forms a prefrontolacrimal. Procrustes-transformed coordinates were significantly different for both collection years and PM/M, but were not significantly different for scanning methods. All shape trends had a significant allometric component. Generally, covariance matrices were more similar during PM than during M across collection years. No support for modularity hypotheses was found; however, the strength of cranial integration was different in the lower jaw and cranium, and through PM/M.