Remodelling of the palate: an additional tool to classify larval salamandrids through metamorphosis

Schematic drawings as well as some cleared and stained preparations of the upper jaw and the palate (mouth roof) of larval (before and during metamorphosis) and transformed specimens of the larviparous Salamandra salamandra are presented to illustrate changes especially of the palate through metamorphosis. We distinguished seven stages ranging from early larvae until fully transformed specimens by using characters easily to see in preserved and anesthetized living specimens by means of a dissection microscope at various magnifications and reflected light. Distinctive characters for classification were growth of the maxillae, the anterolateral expansions and posterior outgrowths (vomerine bar) of the vomeres, complete degradation of both, the bony "bridge" connecting the pterygoid, and the palatine and the palatine itself. Larger specimens (length of ca. ≥ 3 cm) can be inspected non-invasively by fixing them in a simple holder. As we used elements that are always present in metamorphic salamanders either exclusively in their larvae (palatine) or in larvae as well as in transformed specimens (premaxillae, maxillae and vomeres), the classification proposed herein appears to be applicable not only to the type form of S. salamandra, but also to other Salamandridae and, appropriately modified, very probably even to urodele taxa that may considerably differ for instance in the shape of the vomeres and dentition. Obviously metamorphic Urodela appear to be constrained by a largely similar developmental sequence with regard of growth and remodelling of the palate, which may be categorized in a standard manner