Osteichthyans, comprising sarcopterygians and actinopterygians, dominate modern vertebrate biodiversity1–3, yet their pre-Devonian fossil record remains scarce and fragmentary4,5. The oldest articulated sarcopterygian6 and stem osteichthyan7 date to the late Silurian, whereas undisputed actinopterygian fossils in articulation appear only in the Middle Devonian8. Here we report an articulated, near-complete osteichthyan from the early Silurian Chongqing Lagerstätte (approximately 436 million years ago)9–11, representing the oldest osteichthyan occurrence including microfossils. This tiny fish exhibits a fusiform, generalized osteichthyan body outline, with plesiomorphic osteichthyan characters, including the lack of lepidotrichia and the presence of serial median dorsal plates, pectoral and dorsal fin spines and an anal fin spine reported previously exclusively in stem chondrichthyans12 and one placoderm13. It also displays features, such as a single dorsal fin and caudal fulcra, seen commonly in actinopterygians. Bayesian inference and the 50% majority rule consensus of the maximum-parsimony analysis place the new fish on the osteichthyan stem, whereas the strict consensus leaves its position unresolved within osteichthyans. This discovery increases Silurian osteichthyan diversity and further populates the osteichthyan stem group. The morphological disparity among early osteichthyans implies a more extensive Silurian to Early Devonian radiation of bony fishes than previous lines of evidence suggested.
