The first two fossil species of the canthyloscelid genus Synneuron are described based on compression wings. Synneuron eomontana sp. nov. is described from the Middle Eocene Coal Creek Member of the Kishenehn Formation, in the USA, and Synneuron jelli sp. nov. is described from the Lower Cretaceous Koonwarra Fossil Bed of the Korumburra Group, in Australia. The wings are illustrated and compared to the extant species of the genus, to species of the three other recent genera of Canthyloscelidae and to an anisopodid. A phylogenetic analysis of the relationships between the species of Synneuron was performed. The Eocene fossil S. eomontana appears as sister of the pair of recent Holarctic species of the genus, while the Australian Cretaceous species S. jelli is sister of the clade with the species of Synneuron of the northern hemisphere. The sister group of Synneuron is the canthyloscelid clade (Hyperoscelis + Canthyloscelis), for which a middle Jurassic fossil is known. At the early Cretaceous, Gondwana was already separated from Laurasia and the disjunction between the species of Synneuron in Australia and the northern hemisphere clade of the genus suggest a true pangeic origin for the genus. The biology of the canthyloscelid larvae is shaped by its trophic specialization—xylosaprophagous. This suggests that the transition from the Pangean Jurassic gymnosperm‐dominated forests to the late Cretaceous angiosperm‐dominated forests may be related to the low recent diversity of Synneuron or of the canthyloscelids in the world—and maybe to the extinction of the genus in the southern hemisphere. This major turnover of the vegetation type along the Cretaceous may be also somehow related to the complete extinction of other groups of flies strictly associated with gymnosperms, as may be the case of the lower brachyceran family Zhangsolvidae. This speculation needs additional corroboration from other groups, that will become available with the combination of systematics, paleontology and biogeographical information of different early Cretaceous clades.

中文翻译：

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现存稀有的 Synneuron Lundstrom 属（双翅目：Canthyloscledidae）的白垩纪和始新世化石：真正的泛大陆进化枝的证据

Canthyloscelid 属Synneuron的前两个化石物种是基于压缩翼描述的。Synneuron eomontana sp。十一月 描述于美国 Kishenehn 组的中始新世煤溪段和Synneuron jelli sp。十一月 描述于澳大利亚 Korumburra 群的下白垩统 Koonwarra 化石床。对翅膀进行了图示，并将其与该属的现存物种、角蛛科的其他三个最近属的物种以及异足类动物进行了比较。对Synneuron物种之间的关系进行了系统发育分析。始新世化石S. eomontana似乎是该属最近的一对 Holarctic 物种的姐妹，而澳大利亚白垩纪物种S. jelli是北半球Synneuron物种的进化枝的姐妹。Synneuron的姐妹群是Canthyloscelid进化枝（Hyperoscelis  +  Canthyloscelis），其中侏罗纪中期化石是已知的。在白垩纪早期，冈瓦纳已经与劳亚大陆分离，并且Synneuron物种之间的分离在澳大利亚和该属的北半球进化枝表明该属的真正起源。Canthyloscelid 幼虫的生物学是由其营养特化——xylosapropagous 形成的。这表明从盘古侏罗纪裸子植物为主的森林向白垩纪晚期被子植物为主的森林的转变可能与Synneuron最近的低多样性有关。或者世界上的角鳞类动物——也许是南半球该属的灭绝。白垩纪植被类型的这种主要更新也可能与与裸子植物严格相关的其他苍蝇群的完全灭绝有关，例如低端短角科Zhangsolvidae的情况。这种推测需要其他群体的额外证实，这将随着不同早白垩世进化枝的系统学、古生物学和生物地理信息的结合而变得可用。