Lissamphibia
Abstract
Lissamphibians, in the current usage, as well as in phylogenetic nomenclature, is the crown-group of Amphibia. Extant lissamphibians belong to three large clades, Gymnophiona, Caudata and Anura, whose interrelationships remain unclear. The limbless gymnophionans inhabit the tropics and are either aquatic or fossorial; the latter live in superficial, loose soil layers. At a microanatomical level, long bones are most terrestrial and amphibious urodeles, with a tubular diaphysis presenting an open medullary cavity and well-differentiated metaphyses and epiphyses. In longitudinal sections, osteocyte lacunae appear flat and parallel to the sagittal axis of the bones, an aspect confirming that long bone cortices are made of well characterized parallel-fibered bone tissue. In endoskeletal elements, especially the appendicular skeleton and the spine, skeletal neoteny is characteristically related to a delay in endosteoendochondral ossification, and the life-long preservation of calcified cartilages as described in detail by G. S. Terry.