Overview
- Two peer-reviewed studies published March 4 in Nature report Eosteus chongqingensis from early Silurian beds in Chongqing and Megamastax amblyodus from late Silurian strata in Yunnan.
- Parsimony and Bayesian phylogenetic analyses in both papers place the taxa on the osteichthyan stem, preceding the split of ray-finned and lobe-finned lineages.
- Eosteus, about 436 million years old and roughly 3 centimeters long, preserves a complete body with a single dorsal fin and caudal fulcra, lacks lepidotrichia, and bears an anal fin spine known in cartilaginous fishes and placoderms.
- Megamastax, exceeding 1 meter in length around 423 million years ago, is resolved with HRCT to have inner and outer dental arcades with tooth cushions on blunt bases, informing debates over isolated Silurian tooth-cushion fossils.
- Specimens are archived at the IVPP, nomenclature is registered with ZooBank, and phylogenetic datasets along with 3D meshes and supplementary files are available on Figshare for independent verification.