Guiyu oneiros

Guiyu Temporal range: Late Silurian, 425.6±0.9 Ma
Artist's concept of Guiyu oneiros
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Sarcopterygii
Genus:	†Guiyu Zhu et al., 2009
Species:	†G. oneiros
Binomial name
†Guiyu oneiros Zhu et al., 2009

Guiyu oneiros is the earliest articulated bony fish discovered. The generic name Guiyu is a transliteration of the Mandarin 鬼魚 guǐyú "ghost fish" and the specific name oneiros is from Greek ὄνειρος "dream". Fossils of Guiyu have been found in what is now Qujing, Yunnan, China, in a late Silurian marine strata, about 425 million years old. Guiyu remains have been found articulated, missing only the caudal fin. The living fish is estimated to have been around 30 cm long.

Guiyu was described by Chinese palaeontologist Zhu Min (朱敏) and others in 2009, based on a near-complete articulated specimen. It was described as a basal lobe-finned fish with anatomical features of both ray-finned and lobe-finned fishes, although, analysis of the totality of its features place it closer to the class Sarcopterygii (lobe-finned fishes). Guiyu sheds light on the early diversification of bony fishes. This clade, the osteichthyans, splits in two clades: the lobe-finned and the ray-finned (Actinopterygii) fishes. According to new data from Guiyu, this split occurred during the late Silurian period, no later than 419 million years ago (original estimate) or 425 Ma (recent estimate). Guiyu had spine-bearing pectoral girdle, a feature which can be found in primitive gnathostome vertebrates. Other early bony-fish with remarkable features include Andreolepis, Lophosteus, Psarolepis, Ligulalepis and Dialipina.

Guiyu is part of the Xiaoxiang fauna which is rich in fossils representing a marine ecosystem. Found in the late Ludlow-aged Kuanti Formation, the remains were dated using conodonts as index fossils. The Xiaoxiang fauna also includes galeaspids, placoderms and acanthodians.

Classification

Cladogram after the analysis of Yu et al. (2010):

Sarcopterygii	Rhipidistia →Lungfish and Tetrapoda      Styloichthys       Actinistia     Coelacanthiformes      Eoactinistia        Onychodontiformes              Achoania      Psarolepis        Guiyu          Meemannia        Ligulalepis

Description

Guiyu was covered by ganoine tissue, a texture that covers the scales and cranial bones as in early ray-finned fishes. The holotype specimen is about 26 cm in length and about 11 cm in depth. The head possesses about 23% of the body, and the body has a streamlined shape.