such as Seymouria, it may possibly have held a tympanic membrane (eardrum). Complex vertebrae made of multiple components: an intercentrum (wedge-shaped front lower piece), two pleurocentra (upper rear piece), and a vertebral arch/spine (upper projection). The relative development and shape of the elements is highly variable. The labyrinthodonts in life General build Labyrinthodonts were generally amphibian-like in build. They were short-legged and mostly large headed, with moderately short to long tails. Many groups, and all the early forms, were large animals. Primitive members of all labyrinthodont groups were probably true water predators, and various degrees of amphibious, semi-aquatic and semi terrestrial modes of living arose independently in different groups. Some lineages remained waterbound or became secondarily fully aquatic with reduced limbs and elongated, eel-like bodies. Skull With the exception of the snake-like aïstopods, the skulls of labyrinthodonts were massive. The broad head and short neck may have been a result of respiratory constraints. Their jaws were lined with small, sharp, conical teeth and the roof of the mouth bore larger tusk-like teeth. The teeth were replaced in waves that traveled from the front of the jaw to the back in such a way that every other tooth was mature, and the ones in between were young. All teeth were labyrinthodont. The sole exception were the chisel-like teeth of some of the advanced herbivorous diadectomorphs. The skull had prominent otic notches behind each eye and a parietal eye. Post-cranial skeleton The vertebrae were complex and not particularly strong, consisting of numerous, often poorly ossified elements. The long bones of the limbs were short and broad and the ankle had limited mobility and the toes lacked claws, limiting the amount of traction the feet could produce. This would have made most labyrinthodonts slow and clumsy on land. In adulthood, most of the larger species were likely confined to water. Some late Paleozoic groups, particularly microsaurs and seymouriamorphs, were small to medium-sized and appear to have been competent terrestrial animals. The advanced diadectomorphs from the Late Carboniferous and Early Permian were fully terrestrial with stout skeletons, and were the heaviest land animals of their time. The Mesozoic labyrinthodonts were primarily aquatic with increasingly cartilaginous skeleton. Sensory apparatus The eyes of most labyrinthodonts were situated at the top of the skull, offering good vision upwards, but very little lateral vision. The parietal eye was prominent, although there is uncertainty as to whether it was