Osteichthyans, or bony vertebrates, include actinopterygians (teleosts and their relatives) and sarcopterygians (coelacanths, lungfishes and tetrapods). Despite features found in basal actinopterygians (for example, Dialipina and Ligulalepis)1,2,3 and basal sarcopterygians (for example, Psarolepis and Achoania)4,5, the morphological gap between the two lineages remains wide and how sarcopterygians developed a dermal surface covering known as cosmine (composed of a pore–canal network and a single layer of odontodes and enamel) is still poorly known6,7,8,9,10. Here we describe a primitive fossil fish, Meemannia eos gen. et sp. nov., that possesses an actinopterygian-like skull roof and a cosmine-like dermal surface combining a pore–canal network (found in various fossil sarcopterygians) with superimposed layers of odontodes and enamel (previously known in actinopterygians and some acanthodians11,12,13). This 405-million-year-old fish from the Lower Devonian of Yunnan (China) demonstrates that cosmine in many fossil sarcopterygians arose step by step through the acquisition of a pore–canal network followed by the subsequently developed ability to resorb previous generations of odontodes and enamel. Meemannia provides key characters for studying deep osteichthyan phylogeny and indicates a possible morphotype for the common ancestor of actinopterygians and sarcopterygians.
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We thank P. E. Ahlberg for advice and useful discussions, M. Yang for artwork, J. Zhang for photographic work, X. Lu for specimen preparation, and W. Zhang for making thin sections. This work was supported by the Chinese Foundation of Natural Sciences, the Special Funds for Major State Basic Research Projects of China, and the Chinese Academy of Sciences. X.Y. thanks Kean University for faculty research and development support.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
This file includes the character list (I), the data matrix (II), two most parsimonious trees (III), the characters and character states defining major clades (IV), and the references used for constructing the data matrix (V). The phylogenetic analysis shows Meemannia as the most basal sarcopterygian fish below the node of Psarolepis. (PDF 284 kb)
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Zhu, M., Yu, X., Wang, W. et al. A primitive fish provides key characters bearing on deep osteichthyan phylogeny. Nature 441, 77–80 (2006). https://doi.org/10.1038/nature04563
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