title: The Oldest Actinopterygian Highlights the Cryptic Early History of the Hyperdiverse Ray-Finned Fishes.
abstract: Osteichthyans comprise two divisions, each containing over 32,000 living species [1]: Sarcopterygii (lobe-finned fishes and tetrapods) and Actinopterygii (ray-finned fishes). Recent discoveries from China highlight the morphological disparity of early sarcopterygians and extend their origin into the late Silurian [2-4]. By contrast, the oldest unambiguous actinopterygians are roughly 30 million years younger, leaving a long temporal gap populated by fragments and rare body fossils of controversial phylogenetic placement [5-10]. Here we reinvestigate the enigmatic osteichthyan Meemannia from the Early Devonian (∼415 million years ago) of China, previously identified as an exceptionally primitive lobe-finned fish [3, 7, 11, 12]. Meemannia combines "cosmine"-like tissues taken as evidence of sarcopterygian affinity with actinopterygian-like skull roof and braincase geometry, including endoskeletal enclosure of the spiracle and a lateral cranial canal. We report comparable histological structures in undoubted ray-finned fishes and conclude that they are general osteichthyan features. Phylogenetic analysis places Meemannia as an early-diverging ray-finned fish, resolving it as the sister lineage of Cheirolepis [13] plus all younger actinopterygians. This brings the first appearance of ray-fins more in line with that of lobe-fins and fills a conspicuous faunal gap in the otherwise diverse late Silurian-earliest Devonian vertebrate faunas of the South China Block [4].
authors.affiliation: Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 100044 Beijing, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Lu
authors.affiliation: Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK.
authors.forename: Sam
authors.initials: S
authors.lastname: Giles
authors.affiliation: Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK.
authors.forename: Matt
authors.initials: M
authors.lastname: Friedman
authors.affiliation: University of Amsterdam, Science Park 904, 1098 XH Amsterdam, the Netherlands.
authors.forename: Jan L
authors.initials: JL
authors.lastname: den Blaauwen
authors.affiliation: Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 100044 Beijing, China. Electronic address: zhumin@ivpp.ac.cn.
authors.forename: Min
authors.initials: M
authors.lastname: Zhu
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005399:Fishes / Q000033:anatomy & histology*; D005580:Fossils / Q000033:anatomy & histology*; D012886:Skull / Q000033:anatomy & histology