A transitional fossil sheds light on the early evolution of the Staphylinine group of rove beetles (Coleoptera: Staphylinidae)

Rove beetles of the Staphylinine group of subfamilies represent the most species-rich clade of Staphylinidae, which in turn is the most speciose beetle family. While several relationships within the Staphylinine group are well supported by morphological and molecular data alike, the basal relationships within the clade remain unresolved. In particular, understanding the largest radiation on the beetle tree of life is complicated by the absence of early-diverging transitional fossils. Here we describe a new genus and species of the Staphylinine group of subfamilies from the Lower Cretaceous Yixian Formation in eastern China (<i>c</i>. 125 Ma). <i>Paroxyporus fossilis</i> Cai gen. et sp. nov. shares a number of characters with the monogeneric subfamily Oxyporinae, namely its prognathous head with prominent apically curved mandibles, contiguous procoxae, moderately separated mesocoxae and abdominal intersegmental membranes with a ‘brick-wall’ pattern. It, however, shares oval procoxae and ‘U’-shaped abdominal impressions with the monogeneric subfamily Megalopsidiinae. A parsimony analysis of 211 morphological characters recovered <i>Paroxyporus</i> gen. nov. as sister to the whole Staphylinine group except Oxyporinae, linking Oxyporinae and other clades of the Staphylinine group, and it seems to be a stem member of the Staphylinine group. As such, <i>Paroxyporus</i> gen. nov. may represent an early-diverging isolated lineage within the Staphylinine group, a lineage that has been recognized on the basis of morphological data but challenged by some recent molecular studies, or alternatively a stem member of the Staphylinine group. Together with described fossil members of the subfamily Oxyporinae, Paederine and Staphylinine from the Yixian Formation, <i>Paroxyporus fossilis</i> gen. et sp. nov. is one of the earliest representatives of the Staphylinine group in the fossil record, providing an important calibration point for understanding the timing of the early diversification of rove beetles in the Mesozoic. http://zoobank.org/urn:lsid:zoobank.org:pub:40F8F256-7E9F-478E-AC96-1EB1BCE5A02B

隐翅虫科（Staphylinidae）是全球物种最为丰富的甲虫类群，而其中的隐翅虫亚科群（Staphylinine group of subfamilies）则是该科中物种多样性最高的演化支。尽管隐翅虫亚科群内部的多个系统发育关系已得到形态学与分子生物学数据的共同支持，但该演化支的基部亲缘关系仍未得到解决。尤为关键的是，由于缺乏早期分化的过渡性化石，人们难以解析甲虫生命之树上这一规模最大的物种辐射演化事件。本研究描述了采自中国东部下白垩统义县组（约1.25亿年）的隐翅虫亚科群一新属新种：*Paroxyporus fossilis* Cai gen. et sp. nov.。该新类群与仅含单属的隐翅甲亚科（Oxyporinae）具有诸多共有形态特征：其头部为前口式，具显著且顶端弯曲的上颚；前足基节相接，中足基节间距适中；腹部节间膜呈“砖墙状”纹理。但该新属同时与仅含单属的大隐翅甲亚科（Megalopsidiinae）共有卵形前足基节以及“U”形腹部压迹这两处特征。基于211个形态特征的最大简约法分析结果显示，新属*Paroxyporus* gen. nov. 为除隐翅甲亚科外的整个隐翅虫亚科群的姊妹群，连接了隐翅甲亚科与隐翅虫亚科群的其他演化支，且其大概率属于隐翅虫亚科群的基干类群。据此，*Paroxyporus* gen. nov. 可能是隐翅虫亚科群内一个早期分化的孤立演化支——该类群曾基于形态学数据被确立，但近期的部分分子生物学研究对其提出了质疑——亦或是隐翅虫亚科群的基干类群。结合义县组中已发表的隐翅甲亚科、伪隐翅虫亚科（Paederinae）及隐翅虫亚科群化石类群，*Paroxyporus fossilis* gen. et sp. nov. 是隐翅虫亚科群化石记录中最早的代表类群之一，为解析中生代隐翅虫早期多样化的时间节点提供了重要的校准依据。http://zoobank.org/urn:lsid:zoobank.org:pub:40F8F256-7E9F-478E-AC96-1EB1BCE5A02B