Every cloud has a silver lining: X-ray micro-CT reveals Orsunius rove beetle in Rovno amber from a specimen inaccessible to light microscopy

The exceptionally well-preserved and diverse insect fossil record of the Baltic amber group is a unique source for science. However, bubbles and thick layers of white gaseous froth cover numerous inclusions in this type of amber, rendering their examination with traditional light microscopy impossible. Here, we show that X-ray micro-computed tomography can be an efficient tool in such cases. We scanned a completely covered rove beetle (Staphylinidae) fossil in a piece of the relatively recently discovered Rovno amber. The resulting reconstruction was detailed enough to identify the fossil as the first extinct species of Orsunius Assing, an extant genus from the systematically very challenging subtribe Medonina (Lathrobiini, Paederinae). We summarize all previous studies on the origin of gaseous inclusions around fossil specimens in Baltic amber and discuss the technical challenges of using µ-CT where a mostly hollow specimen is surrounded by bubbles of the same density. Since recent Orsunius exclusively occur in the Oriental biogeographic region, we discuss the possible climate change driven speciation scenarios between Orsunius electronefelus sp. nov. and the former. urn:lsid:zoobank.org:pub:8ECD641E-629F-46DC-BC81-217C529ACA84波罗的海琥珀群产出的昆虫化石记录保存状态极佳、类群丰富，是科研领域独一无二的珍贵资源。然而该类琥珀中的诸多内含物常被气泡与厚层白色气态泡沫覆盖，导致传统光学显微镜无法开展观测研究。本研究证明，X射线显微计算机断层扫描（X-ray micro-computed tomography，简称µ-CT）可成为此类场景下的高效研究手段。我们对一块产自近年发现的罗夫诺琥珀（Rovno amber）中、完全被覆盖的隐翅虫科（Staphylinidae）化石完成了扫描，重建结果的细节分辨率足以将该化石鉴定为奥苏纽斯属（Orsunius Assing）的首个灭绝物种。该现生属隶属于分类学研究极具挑战性的麦敦尼纳亚族（Medonina），该亚族隶属于隐翅甲族（Lathrobiini）、隐翅虫亚科（Paederinae）。本研究汇总了此前所有关于波罗的海琥珀中化石标本周围气态内含物成因的研究，并探讨了当近乎中空的标本与密度一致的气泡共存时，使用显微CT开展研究的技术难点。鉴于现生奥苏纽斯属物种仅分布于东洋生物地理区，我们探讨了新种Orsunius electronefelus sp. nov.与该现生类群之间由气候变化驱动的潜在物种形成演化情景。urn:lsid:zoobank.org:pub:8ECD641E-629F-46DC-BC81-217C529ACA84