promammalian
/ˌprəʊməˈmeɪlɪən/ /ˌprəʊmaˈmeɪlɪən/Palaeontology and Zoology. Now chiefly historical
adjective
Relating to or designating a group of (actual or hypothetical) animals representing the ancestors of mammals, or the most primitive form of mammal.
Origin
Late 19th century. From pro- + mammalian, after scientific Latin Promammalia, plural.