Data from: The oldest actinopterygian highlights the cryptic early history of the hyperdiverse ray-finned fishes

Osteichthyans comprise two divisions, each containing over 32,000 living species: 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. 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. 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. 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 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.

硬骨鱼类（Osteichthyans）包含两个亚纲，各现存物种数量均超过32000种：肉鳍鱼亚纲（Sarcopterygii，涵盖肉鳍鱼类与四足类）以及辐鳍鱼亚纲（Actinopterygii，即辐鳍鱼类）。近年来自中国的研究发现揭示了早期肉鳍鱼类的形态分异度，并将其起源时限推至晚志留世。相较而言，目前已确认的最古老辐鳍鱼类化石记录要晚约3000万年，其间存在一段漫长的时间空白，仅存少量系统发育位置存疑的碎片化石与罕见躯体化石。本研究重新审视了产自中国早泥盆世（约4.15亿年前）、此前被认定为极度原始的肉鳍鱼类的神秘硬骨鱼——弥曼鱼（Meemannia）。弥曼鱼兼具被视作肉鳍鱼类亲缘关系证据的“齿鳞质（cosmine）”样组织，以及类似辐鳍鱼类的颅顶骨与脑颅结构，包括喷水孔的内骨骼包裹与颅侧管。我们在确凿归属的辐鳍鱼类中报道了同类组织学结构，并据此认为这些特征属于硬骨鱼类的通用性状。系统发育分析将弥曼鱼定位为早期分化的辐鳍鱼类，将其置于掌鳍鱼（Cheirolepis）与所有更晚期辐鳍鱼类的姊妹群位置。这一结果使辐鳍鱼类的首次出现时限与肉鳍鱼类更为匹配，并填补了华南地块晚志留世至早泥盆世原本物种多样的脊椎动物化石记录中一处显著的类群空白。