LEPTOCHROMINI JAŁOSZYŃSKI & BRUNKE, 2018

Jałoszyński, Paweł, Brunke, Adam J., Yamamoto, Shûhei & Takahashi, Yui, 2018, Evolution of Mastigitae: Mesozoic and Cenozoic fossils crucial for reclassification of extant tribes (Coleoptera: Staphylinidae: Scydmaeninae), Zoological Journal of the Linnean Society 184, pp. 623-652 : 635-636

LEPTOCHROMINI JAŁOSZYŃSKI & BRUNKE TRIB. NOV.

urn:lsid:zoobank.org:act:C45F0203-7DB9-40D2-8B60-6929C30A0FC9

Type genus: Leptochromus Motschulsky, 1855 , here designated.

Diagnosis

Leptochromini differs from all remaining Mastigitae in a unique apomorphy: protrochanteral ventral comb of several (2–7) thick bristles; postgenal bristles are also most likely an autapomorphy of Leptochromini (see Remarks below); and a set of synapomorphies shared with members of other tribes (but in different combinations): scape longer than head, lacking bristles; pedicel unmodified; head capsule strongly transverse; maxillary palpomeres 2 and 3 strongly elongate, palpomere 4 shorter than 3, variable in shape, suboval, subtriangular or nearly rod-like; pronotum with distinct posterior collar; elytra with distinct rows of punctures; mesoventral intercoxal process narrow and elongate, subparallel or slightly narrowing posteriorly; abdominal sternite 8 in males emarginate at middle (this character state remains unstudied in fossils); aedeagus symmetrical or nearly symmetrical, with straight flagellum (also not known in fossils).

Remarks

Postgenal bristles in our analyses were coded assuming their homology in members of the newly defined tribe Leptochromini and Clidicus formicarius , † Palaeoleptochromus schaufussi , † Cretoleptochromus archaicus and † Cretoleptochromus burmiticus . The previous placement of all these genera (except † Cretoleptochromus treated as incertae sedis) in Clidicini suggested such a homology, with thick postgenal bristles of Leptochromus , † Euroleptochromus and † Rovnoleptochromus presumably developed from sparse and conspicuously long, erect setae present in the same area in some species of the Clidicus /† Cretoleptochromus /† Palaeoleptochromus lineage. However, the topology obtained in our parsimony analysis and reconstruction of ancestral character states falsified this hypothesis, in favour of a parallelism, i.e. an independent evolution of long setae and bristles in Clidicini sensu nov. and Leptochromini .

Whether Leptochromini represents the sister-group of † Baltostigini + Mastigini (resolved but unsupported in parsimony analysis) or Clidicini (as found in the Bayesian analysis, but without support, PP = 0.59) remains an unsettled issue. However, the genera placed in Leptochromini form a monophyletic morphological unit in topologies obtained in both analyses, and for this reason they are placed in a separate tribe. Defined as above, Leptochromini differs from Clidicini sensu nov. in the presence of a protrochanteral ventral comb of thick bristles; presence of postgenal bristles (conspicuously thicker than long setae in Clidicini ); maxillary palpomere 4 slightly broadening distad, at least in basal half; and abdominal sternite 8 in males emarginate at middle (but not known in fossils). Moreover, the strongly transverse head capsule in Leptochromini ( Fig. 1C, D) clearly differs from the subrectangular or subtrapezoidal and weakly transverse head of Clidicini ( Fig. 1A, B).