Abstract:

Here the posterior cranial portion of the tetrapodomorph Tungsenia from the Lower Devonian (Pragian, ~409 million years ago) of Yunnan, southwest China, is reported for the first time. The pattern of posterior skull roof and the morphology of the otoccipital region of the neurocranium are described in detail, providing precious insight into the combination of cranial characters of the earliest known tetrapodomorph to date. The posterior cranium of Tungsenia displays a mosaic of features previously linked either to basal dipnomorphs such as Youngolepis (e.g., the well-developed subjugular ridge, the strong adotic process, and the poorly developed fossa bridgei) or to typical tetrapodomorphs (e.g., the lateral dorsal aortae commenced from the median dorsal aorta postcranially). The independent ventral arcual plate is also found in the advanced tetrapodomorph Eusthenopteron. The new endocranial material of Tungsenia further fills in the morphological gap between Tetrapodomorpha (tetrapod lineage) and Dipnomorpha (lungfish lineage) and unveils the sequence of character acquisition during the initial diversification of the tetrapod lineage. The new phylogenetic analysis strongly supports the basalmost position of Tungsenia amongst the tetrapod lineage.

Key words: Yunnan, Early Devonian, Sarcopterygii, Tetrapodomorpha, endocranial character transition

摘要：

首次报道了产于云南昭通早泥盆世布拉格期(约4.09亿年前)最古老的四足形类——奇异东生鱼(Tungsenia paradoxa)头后半部耳枕区的化石材料。东生鱼的耳枕区特征与早期的肺鱼形类,如杨氏鱼非常相似(如具发育的颈下脊,向耳突,以及不发育的桥窝等), 同时也展示出与之后更为进步的四足形类相似的特征(如背侧动脉汇合于颅后,具分离的腹中板等)。这些特征的镶嵌为厘清早期四足形类脑颅特征的获得序列提供了重要的数据。将新获得的东生鱼形态数据加入包含主要早期四足形类分类单元及形态特征的矩阵中进行系统发育分析,结果仍支持东生鱼位于四足动物支系最基干位置。东生鱼耳枕区新材料的发现填补了对早期四足形类脑颅耳枕区结构认识的空白,为认识四足形类后顶甲膜质骨型式及脑颅耳枕区的特征演化提供了新的证据。

关键词: 云南, 早泥盆世, 肉鳍鱼类, 四足形类, 脑颅演化