Department of Geological Sciences, University of Cape Town, Cape Town, South Africa.
Dinosaur Tracks Museum, University of Colorado Denver, Denver, Colorado, United States of America.
PLoS One. 2020 Jan 29;15(1):e0226847. doi: 10.1371/journal.pone.0226847. eCollection 2020.
The Karoo igneous rocks represent one of the largest continental flood basalt events (by volume) on Earth, and are not normally associated with fossils remains. However, these Pliensbachian-Toarcian lava flows contain sandstone interbeds that are particularly common in the lower part of the volcanic succession and are occasionally fossiliferous. On a sandstone interbed in the northern main Karoo Basin, we discovered twenty-five tridactyl and tetradactyl vertebrate tracks comprising five trackways. The tracks are preserved among desiccation cracks and low-amplitude, asymmetrical ripple marks, implying deposition in low energy, shallow, ephemeral water currents. Based on footprint lengths of 2-14 cm and trackway patterns, the trackmakers were both bipedal and quadrupedal animals of assorted sizes with walking and running gaits. We describe the larger tridactyl tracks as "grallatorid" and attribute them to bipedal theropod dinosaurs, like Coelophysis, a genus common in the Early Jurassic of southern Africa. The smallest tracks are tentatively interpreted as Brasilichnium-like tracks, which are linked to synapsid trackmakers, a common attribution of similar tracks from the Lower to Middle Jurassic record of southern and southwestern Gondwana. The trackway of an intermediate-sized quadruped reveals strong similarities in morphometric parameters to a post-Karoo Zimbabwean trackway from Chewore. These trackways are classified here as a new ichnogenus attributable to small ornithischian dinosaurs as yet without a body fossil record in southern Africa. These tracks not only suggest that dinosaurs and therapsids survived the onset of the Drakensberg volcanism, but also that theropods, ornithischians and synapsids were among the last vertebrates that inhabited the main Karoo Basin some 183 Ma ago. Although these vertebrates survived the first Karoo volcanic eruptions, their rapidly dwindling habitat was turned into a land of fire as it was covered by the outpouring lavas during one of the most dramatic geological episodes in southern Africa.
卡拉哈里火成岩代表了地球上最大的大陆溢流玄武岩事件之一（按体积计算），通常与化石遗迹无关。然而，这些上普林尼安-托阿尔阶熔岩流含有砂岩夹层，在火山序列的下部特别常见，偶尔也含有化石。在北部主要卡拉哈里盆地的一个砂岩夹层中，我们发现了二十五只三趾和四趾脊椎动物足迹，包括五条足迹。这些足迹保存在干裂和低振幅、不对称的波纹痕迹中，表明是在低能量、浅、短暂的水流中沉积的。基于足迹长度为 2-14 厘米和足迹模式，足迹制造者是各种大小的两足和四足动物，具有行走和奔跑步态。我们将较大的三趾足迹描述为“grallatorid”，并将其归因于两足兽脚亚目恐龙，如腔骨龙，这是南非早侏罗世常见的一个属。最小的足迹被暂时解释为类似于巴西利斯奇尼的足迹，这些足迹与合弓类足迹制造者有关，这是南冈瓦纳和西南冈瓦纳下至中侏罗纪记录中类似足迹的常见归因。一种中等大小的四足动物的足迹揭示了形态计量参数与卡拉哈里后津巴布韦足迹的强烈相似性，该足迹来自 Chewore。这些足迹在这里被归类为一个新的足迹属，可归因于尚未在南非发现身体化石记录的小型鸟臀目恐龙。这些足迹不仅表明恐龙和兽头亚目在德拉肯斯堡火山活动开始时幸存下来，而且兽脚亚目、鸟臀目和合弓类动物也是大约 1.83 亿年前居住在主要卡拉哈里盆地的最后一批脊椎动物之一。尽管这些脊椎动物在第一次卡拉哈里火山喷发中幸存下来，但当它们的栖息地迅速减少并被喷发的熔岩覆盖时，它们的栖息地变成了一片火海，这是南非最戏剧性的地质事件之一。
