The osteichthyans, or bony fishes and their terrestrial descendants, have been highly successful both on land (tetrapods), and in water (actinopterygians) from at least mid-Devonian until today. However, the origin and the earliest diversification of osteichthyans remain obscure due to a lack of well-understood stem-group, before the split of the two major groups. Previously, the earliest osteichthyan fossils in the Silurian were primarily composed of micro-remains, and articulated osteichthyan fossils were only discovered in the late Silurian (Ludfordian, Ludlow, ~425 Ma) of Yunnan, South China. The early Silurian Chongqing Lagerstätte (late Telychian, Llandovery, ~436 Ma) and the slightly older micro-remain findings from Guizhou offer a unique opportunity to examine the morphology and diversity of early Silurian gnathostomes. A previous report on the Lagerstätte revealed a large number of placoderm fossils and a bizzare, armoured chondrichthyan. Here, we report a completely-preserved osteichthyan from the Chongqing Lagerstätte. The fish is tiny, with a total body length of approximately 3 cm, and is represented by two articulated specimens, including a completely one that reveals the morphology from head to tail. The skull roof is longitudinally divided into two parts, similar to that of the sarcopterygians and the late Silurian Guiyu oneiros. The roofing median dorsal plates or scutes are much more extensively developed than those in Guiyu. The cheek complex and the single, posteriorly placed dorsal fin are actinopterygian-like. Strikingly, the new fish exhibits an anal fin spine, previously thought to be exclusive to “acanthodians”. Phylogenetic analyses resolved the new osteichthyan into the stem-group, suggesting that the character combination displayed by the new taxa may be ancestral in osteichthyan lineage, before the split of two major groups.
Complete bony fish from the early Silurian of China reveals mosaic character combination of stem-group osteichthyan