Abstract:

Tetrapodomorpha comprises all terrestrial vertebrates and their closest fish relatives. The oldest and most basal tetrapodomorphs are known from the Early Devonian of South China, suggesting that South China was a center for the origin of the tetrapod lineage. However, the phylogenetic relationships among early members of the lineage, particularly “osteolepids” (that is equivalent to Osteolepididae), remain poorly resolved. Here we describe a new tetrapodomorph specimen from the Middle Devonian Pearl River Source Scenic Area, Qujing, Yunnan, China. The material includes two anterior cranial portions and a lower jaw, which show overall similarity to Thursius wudingensis from the Middle Devonian of Wuding, Yunnan. High-resolution computed tomography (HRCT) reveals that the skull roof and dermal surface of the lower jaw of the material closely resemble those of T. wudingensis. In contrast, the neurocranial anatomy of the new material differs from those of other Thursius, especially in the morphology of the parasphenoid and the position of the buccohypophyseal foramen. Phylogenetic analysis recovers the new material as a possible sister taxon to T. wudingensis, while the interrelationships of “osteolepids” remain poorly resolved. To further assess the morphological variation and evolutionary relationship among the osteolepiforms, a principal component analysis (PCA) of parietal shield morphology for “osteolepiforms” was conducted, including representatives of Osteolepididae, Canowindridae, and Megalichthyidae. The PCA results are consistent with the phylogenetic analysis, placing the new material in close proximity to T. wudingensis. The new tetrapodomorph material from the Middle Devonian of the Pearl River Source Scenic Area provides new insights into the early evolution of the tetrapod lineage.

Key words: South China, Middle Devonian, Tetrapodomorpha, Osteolepiformes, phylogeny, morphometrics

摘要：

四足形类(Tetrapodomorpha)代表了所有的陆生脊椎动物及其最接近的共同祖先。已知最早的四足形类发现于中国华南早泥盆世地层。然而，有关四足动物支系较为原始类型的系统演化关系仍未完全厘清。报道了产自中国云南曲靖珠江源地区的中泥盆世四足形类化石，新化石材料的颅顶甲和下颌在许多方面与之前报道产自云南武定中泥盆世地层的武定瑟索鱼(Thursius wudingensis)相似。高精度CT扫描与计算机三维重建结果显示，新材料发育良好的鼻下角与武定瑟索鱼相似，但其副蝶骨形态、口垂体管位置与其他已知内颅信息的瑟索鱼类不同。为进一步探讨新材料的系统演化位置，我们对其进行了系统发育分析，分析结果显示，新材料与武定瑟索鱼构成姐妹群，“骨鳞鱼类” 为单系群，但各科的演化关系仍未完全厘清。此外，为了进一步探讨骨鳞鱼类间的系统演化关系，我们对四足形类新材料、武定瑟索鱼、骨鳞鱼科(Osteolepididae)、卡诺文达鱼科(Canowindridae)和巨鱼科(Megalichthyidae)的颅顶甲进行了主成分分析。主成分分析结果支持系统发育分析结果，新材料与武定瑟索鱼位置关系更近，而与其他瑟索鱼类区分开来。珠江源中泥盆世四足形类新材料为我们对四足动物支系的早期演化提供了新的认识。

关键词: 华南地区, 中泥盆世, 四足形类, “骨鳞鱼类”, 系统发育分析, 形态学测量