A new Unenlagiinae (Theropoda: Dromaeosauridae) from the Late Cretaceous of Brazil

The record of unenlagiines in Brazil, except for one dorsal vertebra, is still under debate based on isolated teeth. Here, we describe Ypupiara lopai gen. et sp. nov., the first undoubtful nominal unenlagiine dromaeosaurid species from Brazil, from the Marília Formation (Maastrichtian), Bauru Group, Paraná Basin. The specimen comprises a partial right maxilla (with three teeth in loci) and a right dentary. Ypupiara is characterized by the morphology of the maxilla, presenting restrict number of neurovascular foramina on lateral surface, rectangular and anteroposteriorly expanded interdental plate, teeth with labiolingual diameter more than 3/5 of the rostrocaudal diameter, teeth widely spaced and labiolingually compressed. Our phylogenetic analysis recovers Ypupiara as an unenlagiine based on fluted teeth, and places it as the sister taxon of Austroraptor cabazai due to the ratio between the labiolingual and mediodistal diameters of the teeth more than 3/5. We also erect the new group Unenlagiinia, which includes Unenlagiinae and Halszkaraptorinae clades. Ypupiara nests within this new group based on widely spaced teeth and the lack of mesial/distal carinae in maxillary teeth. The morphology of the teeth is similar to Buitreraptor gonzalezorum, although the proportions are markedly distinct. The teeth and comparisons with other Unenlagiinia also support that fish was part of the diet for Ypupiara. We also performed a Parsimony Analisys of Endemicity, which suggests that the presence of unenlagiines in Brazilian Upper Cretaceous outcrops is explained by dispersion or extinct events. The new species provides new information on the evolution of Gondwanan dromaeosaurids, and its preserved teeth provides new data to assign isolated dromaeosaurid teeth from Bauru Group.

巴西境内的半鸟亚科（Unenlagiinae）化石记录，除一枚背椎外，目前仍仅依靠孤立牙齿存在学术争议。本文记述了产自巴拉那盆地包鲁群马里利亚组（马斯特里赫特阶）的新属新种Ypupiara lopai gen. et sp. nov.，这是巴西境内首个确凿定名的驰龙科（Dromaeosauridae）半鸟亚科物种。该标本包含一件带有3枚原位牙齿的部分右上颌骨，以及一块右齿骨。Ypupiara的鉴定特征如下：上颌骨侧面神经血管孔数量有限，具矩形且前后向扩展的齿间板；牙齿唇舌径大于吻尾径的3/5，齿间距宽阔且唇舌侧压扁。基于牙齿具纵棱的特征，系统发育分析将Ypupiara归入半鸟亚科；且因其牙齿唇舌径与近远中径之比大于3/5，将其定为卡扎奥斯盗龙（Austroraptor cabazai）的姊妹群。本文同时建立新类群半鸟亚总类群（Unenlagiinia），包含半鸟亚科与哈兹卡盗龙亚科（Halszkaraptorinae）演化支。基于牙齿间距宽阔且上颌齿无近中/远中脊的特征，Ypupiara嵌套于该新类群之中。其牙齿形态与冈氏布鲁盗龙（Buitreraptor gonzalezorum）相似，但比例特征存在显著差异。通过牙齿形态及与其他半鸟亚总类群的对比研究，可推断鱼类曾为Ypupiara的食物组成之一。本文还开展了特有性简约分析，结果显示巴西上白垩统露头中的半鸟亚科化石分布，可通过扩散事件或灭绝事件得到解释。该新物种为冈瓦纳大陆驰龙科的演化研究提供了新的信息，其保存的牙齿也为包鲁群中孤立驰龙科牙齿的分类归属提供了新的数据支撑。