1. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, PO Box 643, Beijing 100044, China
2. Department of Biological Sciences, Kean University, Union, New Jersey 07083, USA

Correspondence to: Min Zhu¹ Correspondence and requests for materials should be addressed to M.Z. (e-mail: Email: zhumin@ht.rol.cn.net).

Abstract

The relationship of the three living groups of sarcopterygians or lobe-finned fish (tetrapods, lungfish and coelacanths) has been a matter of debate^{1, 2, 3, 4, 5}. Although opinions still differ, most recent phylogenies suggest that tetrapods are more closely related to lungfish than to coelacanths^{6, 7, 8, 9, 10}. However, no previously known fossil taxon exhibits a concrete character combination approximating the condition expected in the last common ancestor of tetrapods and lungfish—and it is still poorly understood how early sarcopterygians diverged into the tetrapod lineage (Tetrapodomorpha)⁷ and the lungfish lineage (Dipnomorpha)⁷. Here we describe a fossil sarcopterygian fish, Styloichthys changae gen. et sp. nov., that possesses an eyestalk and which exhibits the character combination expected in a stem group close to the last common ancestor of tetrapods and lungfish. Styloichthys from the Lower Devonian of China bridges the morphological gap between stem-group sarcopterygians (Psarolepis and Achoania)¹⁰ and basal tetrapodomorphs/basal dipnomorphs. It provides information that will help in the study of the relationship of early sarcopterygians, and which will also help to resolve the tetrapod–lungfish divergence into a documented sequence of character acquisition.