English: Fossils of Megamastax amblyodus. (A–E) Holotype mandible (IVPP V18499.1) in (A) lateral, (B) lingular, and (C) dorsal views; close-up of prearticular bone, showing surface ridges (D), and close-up of the marginal dentition in lingual view (E). (F–H) Partial mandible (V18499.2) in (F) lateral, (G) lingular, and (H) dorsal views. (I) Right maxilla (V18499.3) in lateral view. (J) Reconstruction of (J1) Guiyu oneiros alongside hypothetical silhouettes of (J2–3) Megamastax with superimposed fossil outlines (drawn by B.C.). The (J2) smaller fish is based on the V18499.1 and V18499.3, the (J3) larger on V.18499.2. ar.psym, knob-like parasymphysial structure; Co 1–4, coronoids 1–4; coT 1–8, coronoid teeth 1–8; De, dentary; fo.add, adductor fossa; fo.gl, glenoid fossa; fo.Mk, Meckelian foramen; Id, infradentary; mpl, mandibular pit line; maT, marginal teeth; oaMx, overlap area for maxilla and quadratojugal; Pat, prearticular; sym, area for parasymphysial plate; tr, indented track bordering splenial.