Internal cranial anatomy of Early Triassic species of †Saurichthys (Actinopterygii: †Saurichthyiformes): implications for the phylogenetic placement of †saurichthyiforms

Background: †Saurichthyiformes was a successful group of latest Permian-Middle Jurassic predatory actinopterygian fishes and constituted important and widely-distributed components of Triassic marine and freshwater faunas. Their systematic affinities have long been debated, with †saurichthyiforms often being aligned with chondrosteans, a group today comprising sturgeons and paddlefishes. However, their character-rich endocranial anatomy has not been investigated in detail since the first half of the 20th century. Since that time, major advances have occurred in terms of our understanding of early actinopterygian anatomy, as well as techniques for extracting morphological data from fossils.
Results: We used µCT to study the internal cranial anatomy of two of the stratigraphically oldest representatives of †Saurichthys, from the Early Triassic of East Greenland and Nepal. Our work revealed numerous previously unknown characters (e.g., cryptic oticooccipital fissure; intramural diverticul...

研究背景：†锯颌鱼形目（Saurichthyiformes）是一类繁盛于晚二叠世至中侏罗世的掠食性辐鳍鱼类，曾是三叠纪海洋与淡水动物群中重要且分布广泛的组成类群。其系统发育亲缘关系长期存在争议，以往常将锯颌鱼形类与软骨硬鳞类（Chondrostei）归为一类，现生软骨硬鳞类包含鲟形目鱼类与匙吻鲟科物种。然而，自20世纪上半叶以来，其富含特征的颅内部解剖结构尚未得到细致研究。在此之后，学界对早期辐鳍鱼类解剖结构的认知以及从化石中提取形态学数据的技术均取得了重大进展。
研究结果：本研究利用显微CT（µCT）对来自东格陵兰与尼泊尔早三叠世地层的两种地层学上最古老的锯颌鱼属（Saurichthys）类群的颅内部解剖结构开展了研究。本研究揭示了诸多此前未被发现的解剖学特征（例如：隐蔽的耳枕裂隙；壁内憩室……