Guiyu oneiros

Guiyu oneiros is an extinct species of early bony fish, one of the earliest articulated bony fish yet discovered, placed within the clade Osteichthyes and named by Zhu and colleagues in 2009. Its fossils date to the Late Silurian period, specifically the Ludlow epoch, roughly 425.6 million years ago, with the age established using conodont index fossils. They were recovered from the Kuanti Formation, in late Silurian marine strata near what is now Qujing in Yunnan Province, China, part of the fossil rich Xiaoxiang fauna. The holotype specimen measures about 26 centimeters in length, with an estimated living length of around 30 centimeters. The fish combines several primitive features characteristic of placoderms with anatomical traits found in both ray finned and lobe finned fishes, and its discovery indicates that the split between the ray finned and lobe finned fish lineages had already occurred by the late Silurian.