Temnospondyls ' vertebrae are divided into several segments . In living tetrapods , the main body of the vertebra is a single piece of bone called the centrum , but in temnospondyls , this region was divided into a pleurocentrum and intercentrum . Two types of vertebrae are recognized in temnospondyls : stereospondylous and rhachitomous vertebrae . In rhachitomous vertebrae , the intercentra are large and wedge @-@ shaped , and the pleurocentra are relatively small blocks that fit between them . Both elements support a spine @-@ like neural arch , and well @-@ developed interlocking projections called zygapophyses strengthen the connections between vertebrae . The strong backbone and strong limbs of many ratchitomous temnospondyls allowed them to be partially , and in some cases fully , terrestrial . In stereospondylous vertebrae , the pleurocentra have been lost entirely , with the intercentra enlarged as the main body of the vertebrae . This weaker type of backbone indicates the stereospondylous temnospondyls spent more time in water .