Middle-Upper Ordovician to Late Devonian |regnum = Animalia |phylum = Chordata |subphylum = Vertebrata |unranked_subphylum = Agnatha |classis = Thelodonti |subdivision_ranks = Subgroupings(unranked, see Turner 1991) |subdivision = Theleodontina Loganiida Katoporida }} There's much debate over whether the group of Palaeozoic fish known as the Thelodonti (formerly coelolepids) represent a monophyletic grouping, or disparate stem groups to the major lines of jawless and jawed fish. Thelodonts (f… (More on Thelodonti)