The first land animals colonised the earth about 350 million years ago. They were fish, marine amphibians that had evolved on land and became partially terrestrial. Their bodies changed to better cope with life on land, including a larger brain and spine to support their new way of life.
Over the next 160 million years, amniote (a group that includes mammals and reptiles) evolved from marine amphibians into terrestrial creatures. Amniote skulls became more streamlined, featuring flattened sides that let them move through trees more easily. Their spinal cord lengthened so they could reach higher up on tree trunks, and their limbs evolved into hands with fingers that could grip objects securely.