A diplodocid sauropod dinosaur from the Late Jurassic Cañadón Calcáreo Formation of Chubut, Argentina

ABSTRACTLate Jurassic dinosaur faunas from the Southern Hemisphere are still poorly known, and it thus remains unclear whether or not the famous Tendaguru fauna (Kimmeridgian–Tithonian, Tanzania) represents a typical Gondwanan dinosaur assemblage of that time. In South America, only the Oxfordian–Kimmeridgian Cañadón Calcáreo Formation of Chubut Province, Argentina, has yielded more than isolated Late Jurassic dinosaur remains so far. Here we report fragmentary remains of a dipolodocid sauropod from this unit, representing the first record of this family from the Late Jurassic of South America. Incorporating the basal macronarian <i>Tehuelchesaurus</i>, an unidentified brachiosaurid, the dicraeosaurid <i>Brachytrachelopan</i>, and the diplodocid described here, the taxonomic composition of the sauropod fauna from the Cañadón Calcáreo Formation is remarkably similar to that of the Tendaguru Formation, but also to roughly contemporaneous faunas in North America and Europe. The diverse non-neosauropodan sauropod fauna known from the early Middle Jurassic (Aalenian–Bajocian) of the same depositional basin within Chubut Province is congruent with the dominance of non-neosauropodan sauropods in continental faunas globally to at least the Bathonian. These assemblages suggest a rapid faunal turnover within sauropod faunas in the late Middle Jurassic-earliest Late Jurassic at least in western Pangea, through which basal eusauropods were replaced by diplodocoid and macronarian neosauropods. Taking paleogeographical reconstructions into account, this faunal replacement might have taken place in a surprisingly short time interval of maximally five million years close to the end of the Middle Jurassic.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

摘要：南半球晚侏罗世（Late Jurassic）恐龙动物群至今仍所知甚少，因此著名的坦达古鲁动物群（坦桑尼亚，基默里奇阶（Kimmeridgian）-提通阶（Tithonian））是否代表当时典型的冈瓦纳（Gondwanan）恐龙组合，目前仍不明确。迄今为止，南美洲仅阿根廷丘布特省的牛津阶（Oxfordian）-基默里奇阶卡尼亚东·卡尔卡雷组（Cañadón Calcáreo Formation）产出了不止零散的晚侏罗世恐龙化石遗存。本次研究报道了该地层中一件双腔龙科（dipolodocid）蜥脚类的零碎化石，这是该科在南美洲晚侏罗世的首个化石记录。结合基干大鼻龙类（macronarian）特维尔切龙（<i>Tehuelchesaurus</i>）、一件未确定分类的腕龙科（brachiosaurid）标本、双棘龙科（dicraeosaurid）短颈龙（<i>Brachytrachelopan</i>）以及本次描述的双腔龙科类群，卡尼亚东·卡尔卡雷组的蜥脚类动物群分类组成不仅与坦达古鲁组极为相似，也与北美和欧洲的同期动物群大致相仿。产自丘布特省同一沉积盆地的中侏罗世早期（阿连阶（Aalenian）-巴柔阶（Bajocian））的多样非新蜥脚类（non-neosauropodan）蜥脚类动物群，与全球至少至巴通阶（Bathonian）的陆相动物群中非新蜥脚类占据主导地位的格局相一致。这些化石组合表明，至少在盘古大陆（Pangea）西部，中侏罗世晚期至最早晚侏罗世期间，蜥脚类动物群内部发生了快速的类群更替：基干真蜥脚类（basal eusauropods）被梁龙超科（diplodocoid）与大鼻龙类新蜥脚类（neosauropods）所取代。结合古地理重建结果来看，此次动物群更替可能发生在中侏罗世末期前后的极短时间窗口内，最长跨度仅约500万年。

补充数据——本文的补充材料可通过www.tandfonline.com/UJVP免费获取