The pelycosaurs (from Greek πέλυξ pelyx "bowl" or "axe" and σαῦρος sauros "lizard") are an informal grouping (previously considered an order) composed of basal or primitive Late Paleozoic synapsids, also known as mammal like reptiles. They consist of all synapsids except for the therapsids and their descendants. Some species were quite large and could grow up to 3 metres (10 ft) or more, although most species were much smaller. Because more advanced groups of synapsids evolved directly from 'pelycosaurs', the term had fallen out of favor among scientists by the 21st century, and is only used informally, if at all, in the modern scientific literature.