Pelycosaur

The pelycosaurs are an informal grouping composed of basal or primitive Late Paleozoic synapsids, sometimes erroneously referred to as "mammal-like reptiles". They consist of all synapsids except for the therapsids and their descendants. Some species were quite large, growing to a length of 3 metres 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. The supplied etymology presents a problem, as follows: pelycosaur has the basically supplied meaning 'basin lizard', but there is an original etymological mismatch in that Greek pélix is 'wooden bowl' and pelíkē 'basin', whereas pélyx is 'ax' like pélekys 'double-edged ax'. This imperfect term pelycosaur has been fairly well abandoned by paleontologists because it no longer matches cladistic features.