The relationship of the three living groups of sarcopterygians or lobe-finned fish (tetrapods, lungfish and coelacanths) has been a matter of debate1,2,3,4,5. Although opinions still differ, most recent phylogenies suggest that tetrapods are more closely related to lungfish than to coelacanths6,7,8,9,10. 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.
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We thank M. M. Chang and P. E. Ahlberg for advice and discussions, K. S. Thomson for comments and corrections, M. Yang for artwork, J. Zhang for photographic work, and X. Lu for specimen preparation. This work was supported by the Special Funds for Major State Basic Research Projects of China, the Chinese Foundation of Natural Sciences, and the US National Geographic Society. X.Y. thanks Kean University for faculty research and development support.
The authors declare that they have no competing financial interests.
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Zhu, M., Yu, X. A primitive fish close to the common ancestor of tetrapods and lungfish. Nature 418, 767–770 (2002). https://doi.org/10.1038/nature00871
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