ABSTRACT

Thunnosaurian ichthyosaurs were one of the most successful lineages of Mesozoic tetrapods in terms of adaptation to a pelagic lifestyle. Among them, the ophthalmosaurids are of particular interest. Their fossils document an early widespread distribution, including high northern and southern latitudes soon after they appear at the Aalenian–Bajocian boundary, becoming almost the only surviving lineage of ichthyosaurs for approximately 76 million years until their extinction at the end of the Cenomanian (Late Cretaceous). Evolutionary innovations that could have been involved in their remarkable evolutionary success are still poorly understood. Two regions of the skeleton, involved in two vital functions – breathing and swimming – depict notable variation among ophthalmosaurids: the narial region and the proximal forefin configuration (i.e., stylopodium-zeugopodium-mesopodium pattern). Here, we describe Catutosaurus gaspariniae gen. et sp. nov., a new Tithonian (Late Jurassic) ophthalmosaurid from the northwest of Patagonia, Argentina. The new taxon depicts a peculiar pattern of the narial opening and forefin. Catutosaurus has an ‘ophthalmosaurine-like’ skull with reduced cheek, triangular squamosal, slender and delicate snout and rounded tooth roots; and ‘platypterygiine-like’ forefin composed by the typical polygonal and tightly packed elements and a broad articulation between the stylopodium and zeugopodial row. Phylogenetic analysis retrieves Catutosaurus nested within basal ophthalmosaurids, at the base of a large clade named here as Panplatypterygiine. New information provided by Catutosaurus suggests that changes in the narial region and complexity of the stylopodium–zeugopodium articulation occurred independently among ophthalmosaurids and not in a stepwise manner along with the evolution of the clade.

http://zoobank.org/urn:lsid:zoobank.org:pub:FDB6C301-BAE5-4212-9310-BE09E24605F9

摘要

就适应远洋生活方式而言，雷龙鱼龙是中生代四足动物中最成功的谱系之一。其中，眼科龙类是特别令人感兴趣的。它们的化石记录了早期的广泛分布，包括在它们出现在 Aalenian-Bajocian 边界后不久就分布在高北纬和南纬，几乎成为鱼龙唯一幸存的谱系，大约 7600 万年，直到它们在 Cenomanian 末期（晚白垩世）灭绝）。可能与它们显着的进化成功有关的进化创新仍然知之甚少。骨骼的两个区域涉及两个重要功能——呼吸和游泳——描绘了眼科龙类之间的显着变化：鼻骨区域和近端前鳍构造（即，柱基-zeugopodium-mesopodium 模式）。在这里，我们描述Catutosaurus gaspariniae gen。等 sp. 11 月，来自阿根廷巴塔哥尼亚西北部的一种新的提通阶（晚侏罗纪）眼龙科。新的分类群描绘了鼻孔和前翅的特殊模式。Catutosaurus有一个“眼突龙类”的头骨，脸颊缩小，三角形鳞状，细长而精致的鼻子和圆形的牙根；和由典型的多边形和紧密排列的元素和花柱基和 zeugopodial 行之间的广泛关节组成的“类似鸭嘴兽”的前鳍。系统发育分析检索到猫头龙嵌套在眼底目龙科中，位于此处命名为 Panplatypterygiine 的大型进化枝的底部。Catutosaurus提供的新信息 表明在眼科龙科中，柱状足 - zeugopodium 关节的鼻部区域和复杂性的变化是独立发生的，而不是随着进化枝的进化而逐步发生的。

http://zoobank.org/urn:lsid:zoobank.org:pub:FDB6C301-BAE5-4212-9310-BE09E24605F9