Abstract:

The recent finding of a fossil entombed in a Late Cretaceous amber - Oculudentavis khaungraae - was claimed to represent a humming bird-sized dinosaur. Regardless of the intriguing evolutionary hypotheses about the bauplan of Mesozoic dinosaurs (including birds) posited therein, this enigmatic animal demonstrates various morphologies resembling lizards. If Oculudentavis was a bird, it challenges several fundamental morphological differences between Lepidosauria and Archosauria. Here we reanalyze the original computed tomography scan data of the holotype of Oculudentavis khaungraae (HPG-15-3). Morphological evidences demonstrated here highly contradict the avian or even archosaurian phylogenetic placement of the species. In contrast, our analysis revealed multiple skull morphologies of HPG-15-3 resembling those of squamates, including pleurodont marginal teeth, an open infratemporal fenestra, and the presence of palatal dentition. Based on these new morphological information, the phylogenetic position of Oculudentavis was analyzed in a data matrix sampling across the Diapsida. Taxon sampling of the data matrix included multiple species of lizards, birds, and major clades in Lepidosauromorpha and Archosauromorpha. In the strict consensus tree, Oculudentavis is nested within Squamata. These results show that morphology of the Oculudentavis khaungraae holotype supports a squamate rather than avian or dinosaurian affinity of the species.

Key words: Burma, Cretaceous, bird, lizard, Diapsida, Squamata, Oculudentavis

摘要：

最近在白垩纪晚期缅甸琥珀中报道了一件小型头骨化石,原论文作者将其鉴定为一蜂鸟大小的鸟翼类(Avialae)恐龙,并命名为宽娅眼齿鸟(Oculudentavis khaungraae)。基于这件标本,原论文提出了中生代恐龙(包括鸟翼类)体型演化和生态类型的种种假设。但原论文的插图和描述均显示这件头骨呈现出多个鳞龙类的典型形态学特征,这些特征很少在主龙类中出现。原论文先验地将标本鉴定为鸟翼类,继而进行仅包括鸟翼类作为内类群的系统发育分析。该分析的取样过于局限,不能对其系统位置归属提供有价值的参考。本文对宽娅眼齿鸟正型标本的计算机断层扫描原始数据重新进行了重建、渲染和分析,结果揭示了多个新的头骨形态学特征,包括侧生齿、开放的下颞孔以及头骨腭面着生有腭齿等,这些均为典型的鳞龙类/有鳞类特征,不支持其主龙类,遑论鸟翼类的系统位置归属。基于上述新的形态学发现,使用一双孔类(Diapsida)形态特征矩阵重新分析了眼齿鸟的系统演化位置。数据矩阵的分类单元涵盖了蜥蜴、鸟类和鳞龙形类与主龙形类中的主要支系。分析所得的严格合意树明确了眼齿鸟属于鳞龙形类中的有鳞类。因此,宽娅眼齿鸟的正型标本显示了足够丰富的形态学信息,完全能够指示眼齿鸟的系统分类位置应为有鳞类,而不是鸟翼类或非鸟恐龙。

关键词: 缅甸, 白垩纪, 鸟类, 蜥蜴, 双孔类, 有鳞类, 眼齿鸟