1 Introduction.
The Paederinae is one of the hyper-diverse subfamilies of the Staphylinidae with 225 (1 extinct) genera, and approximately 7 584 (35 extinct) species (Bogri et al. 2020). This subfamily remains largely unexplored, both phylogenetically and taxonomically (Schomann and Solodovnikov 2017), and is known as one of the most challenging subfamilies to study (Żyła et al. 2021). This is due to the shortage of phylogenies undertaken. In addition, its phylogeny-based tribal and sub-tribal classification schemes still need an extensive revision, while many genera await proper delimitation (Bogri et al. 2020). The challenge is exacerbated by its high species richness, diversity and abundance, and having few experts studying this group (Żyła et al. 2021). Recently, more researchers are studying the subfamilies of the Staphylinidae.
The Paederinae was divided into four tribes, namely: Pinophilini, Paederini, Cylindroxystini and Lathrobiini (Schomann and Solodovnikov 2017). Recently, Żyła et al. (2021) conducted the most comprehensive phylogenetic analysis of the Paederinae, based on multiple genetic loci, incorporating the broadest sampling of the taxa. The study reduced the Paederinae into three monophyletic tribes, namely the Pinophilini and Paederini which are sister groups of one another, and which together are the sister group of the Lathrobiini. In the study, the Cylindroxystini were subsequently demoted to a group within the Lathrobiini (Żyła et al. 2021). Furthermore, according to Żyła et al. (2021), the sister clades of the Paederinae are either the Euasthetinae or Staphylininae. However, most phylogenetic studies (e.g., Grebennikov and Newton 2009; Solodovnikov et al. 2013; and McKenna et al. 2015) found that the Paederinae and Staphylininae are sister groups. Surprisingly, the relationship between Paederinae and Staphylininae only found weak support in a recent study by Lü et al. (2020).
The split between Paederinae and Staphylininae is estimated to have occurred during the Late Jurassic (156.6 Ma), using mitogenomic sequencing (Hernando and Andujar 2021). More recently, this notion has been supported by Lü et al. (2020), who analysed four nuclear and two mitochondrial gene sequences, and estimated that the two subfamilies originated between 147.58 and 160.41 million years ago, respectively.
The Mesozoic fossil record of the Paederinae is restricted to the Cretaceous (Table 1). So far, none have been recorded between the Triassic and Jurassic ages. Schomann and Solodovnikov (2012) assigned the genus Apticax and A. solidus from the Nova Olinda Member of the Crato/Santana Formation in north-eastern Brazil to the Staphylininae + Paederinae lineage, but disclosed that the small number of diagnostic features do not allow for a definite placement in any of the 33 subfamilies of the Staphylinidae.
Solodovnikov et al. (2013) described Mesostaphylinus elongatus ,M. yixianus , and M. antiquus from the Early Cretaceous deposit, Yixian Formation of China, based on phylogenetic analysis of both extinct and extant taxa. These were placed “incertae sedis ” within the Paederinae, due to lack of diagnostic features. Żyła et al. (2019) described two inclusions from the Cretaceous Burmese amber of Myanmar, Diminudon schomannae and D. kachinensis(Lathrobiini), by a combination of morphological and molecular datasets. Shaw et al. (2020) described the earliest record of the Pinophilini,Cretoprocirrus trichotos from Burmese amber of Myanmar. Bogri et al. (2018) described Dysanabatium kechrimparense , D. aenaum , D. damgaardi , and D. johannesi from the Baltic amber of Russia, to address a connection between co-occurrence of thermophilic and temperate insect taxa and Eocene climate change. In addition, Bogri et al. (2020) described Micrillus electrus andScymbalium phaethoni from the Baltic amber of Russia, based on diagnostic morphological character matrices of both genera.
In total, the fossil record of the Paederinae encompasses 40 species from 12 genera: Achenium Curtis 1826, Apticax Schomann and Solodovnikov 2012, Cretoprocirrus Shaw et al. 2020,Diminudon Żyła et al. 2019, Dysanabatium Bernhauer 1915,Lathrobium Gravenhorst 1802, Lithocharis Dejean 1833,Miolithocharis Wickham 1913, Medon Stephens 1833,Mesostaphylinus Zhang 1988, Orsunius Assing 2011 andPaederus Lin et al. 2018; ranging from Cretaceous to Miocene. This summary is given by Żyła et al. (2019), with an addition ofCretoprocirrus (Shaw et al. 2020). Notably, all the Cenozoic fossils have been assigned to the tribe Lathrobiini (Żyła et al. 2019).
Table 1: Species list of the Paederinae (Coleoptera: Staphylinidae). Updated from Żyła et al. (2019).