I want to introduce a new paper by Paweł Jałoszyński. This March in Systematic Entomology, Paweł described a new extinct genus and species of clidicine Ant-like stone beetle, ✝Euroleptochromus sabathi together with a phylogenetic analysis of the supertribe Mastigitae. This species is interesting because unlike the previously described fossil clidicine ✝Palaeoleptochromus, ✝Euroleptochromus has an elongate maxillary palpus with a setose process and a genal setose process similar to the extant sister genus Leptochromus.
Hopefully you can see the genal and palpal setoses processes in the photo above of Leptochromus agilis.
Paweł, in his phylogenetic analysis also sheds light on the enigmatic position of Papusus, a highly unusually staphylinid that has apparently adapted to living in the deserts of Western North America.
Papusus has been thought to be a member of the tribe Clidicini, but according this new study, Papusus is either the earliest diverging Clidicini or sister to Leptomastacini + remaining Clidicini. Once staphylinids abbreviated their elytra, biologically, it appears that ability to adapt to arid environments were lost. Presumably the rate of water loss increased with the exposure of the abdominal dorsal surface. Given this, the arid environmental preference of Papusus is intriguing and divergent adaptive regimes may be responsible for poor resolution in phylogenetic placement of the genus – based on morphology.
I think that this is an impressive beginning to elucidating the evolutionary history of the Masitigiate – so so exciting, I love scydmaenines, and their congruent morphology with pselaphines is spectacular. But, I do believe that several pertinent questions persist:
- What, if any, are the adaptive adaptive advantages of the setose maxillary and genal processes? Prey capture?
- Is the phylogenetic placement of Papusus based on morphological evidence accurate? Could the adaptive evolutionary changes, induced by the unique environmental pressures on Papusus, have complicated the inference into the proper phylogenetic placement of the genus within the Mastigitae?
- Are the branch length estimates based on morphological data precise? If we were to include molecular data for the extant taxa, would we get a different view on evolutionary history of the Mastigitae?
- Finally, would divergence time estimates of the Mastigitae represent a congruent portrayal of biogeographical history?
Oh, and here’s the reference to the paper:
Jałoszyński, P. 2012. Description of Euroleptochromus gen.n. (Coleoptera, Staphylinidae, Scydmaeninae) from Baltic amber, with discussion of biogeography and mouthpart evolution within Clidicini. Systematic entomology, 37(2): 346-359.