Thelodonti

Thelodonti (from Greek: "nipple teeth") is a class of extinct Palaeozoic jawless fishes with distinctive scales instead of large plates of armor. These fish lived in both freshwater and marine environments, first appearing during the Late Ordovician, and perishing shortly after the Frasnian–Famennian extinction event in the Late Devonian.

There is much debate over whether the group represents a monophyletic grouping, or disparate stem groups to the major lines of jawless and jawed fish.