Overview
- Two back-to-back Nature cover papers published March 4, 2026 report Eosteus chongqingensis (~436 million years old) and Megamastax amblyodus (~423 million years old) from South China.
- Eosteus from Xiushan, Chongqing, is a near-complete 3-centimeter osteichthyan preserving a full body with a single dorsal fin, caudal fulcra, absence of lepidotrichia, and an anal fin spine.
- High-resolution CT and 3D reconstructions detail the complete cranial anatomy of Megamastax from Yunnan, a fish exceeding one meter that ranks as the largest known Silurian vertebrate.
- Megamastax shows inner tooth cushions on blunt bases alongside an outer tooth row, resolving the long-debated affinities of isolated Silurian tooth cushions from the Baltic region.
- Phylogenetic analyses place both fossils on the bony-fish stem before the ray-finned and lobe-finned split, filling a key pre-Devonian gap and reinforcing South China as a cradle of early jawed-vertebrate evolution.