The taxonomic status of the Late Cretaceous dromaeosaurid Linheraptor exquisitus and its implications for dromaeosaurid systematics

Abstract

The dromaeosaurid Linheraptor exquisitus was named in 2010 based on a nearly complete skeleton recovered from the Upper Cretaceous Wulansuhai Formation at the Gate Locality, in Bayan Mandahu, western Inner Mongolia, China. However, threewo recent studies regarded L. exquisitus as a subjective junior synonym of Tsaagan mangas, a dromaeosaurid from the Upper Cretaceous Djadokhta Formation of the Ukhaa Tolgod locality, Mongolia. Here we refute this synonymy based on about 60 morphological features that distinguish L. exquisitus from T. mangas. Many of these features are based on new observations from previously unprepared areas of the L. exquisitus holotype, most notably from the left lateral side of the skull. These observations underscore and strengthen our original taxonomic separation of L. exquisitus and T. mangas. Evidence from L. exquisitus points to an unexpectedly complex distribution of derived osteological features amongst dromaeosaurids, because this species possesses features that were previously identified as autapomorphies of T. mangas or indeed of various other dromaeosaurids. Our review demonstrates that the proposed synonymy between L. exquisitus and T. mangas ignores many subtle morphological variations. Increased taxonomic sampling breaks down seemingly obvious diagnostic differences into more subtle morphological variations, which are potentially of great importance for fine-scale phylogenetic analyses. Rigorous quantitative methods using continuous data represent a promising way to exploit this type of information in future systematic studies.

馳龍類的精美臨河盜龍(Linheraptor exquisitus)於2010年基於一件近完整骨架命名，化石採自內蒙古西部巴彥滿達呼大門地點上白堊統烏蘭蘇海組。然而，最近三項研究認為精美臨河盜龍是蒙古烏哈托喀地點上白堊統捷達克赫塔組發現的白魔龍(Tsaagan mangas)的晚出異名。本文依據61個形態學特徵區分精美臨河盜龍和白魔龍，否認了上述觀點。許多特徵來自對精美臨河盜龍正型標本先前未修理部分，特別是頭骨左側的觀察。這些新觀察支持和加強了我們先前認為的精美臨河盜龍和白魔龍屬於兩個不同屬種的觀點。精美臨河盜龍具有的一些特徵之前被認為是白魔龍或者其他馳龍類的自近裔特徵，這表明進步的骨骼特徵在馳龍類中的分佈異常複雜。認為精美臨河盜龍和白魔龍為同物異名的觀點實際上忽略了很多微小的形態變異。增加分類取樣可以將那些看似顯著的鑑定特徵轉化為更加細微的形態變異，而這些形態變異對於精細的系統發育分析具有潛在的重要意義。在未來的研究中，利用連續數據的嚴格定量方法，有助於處理類似信息。