Insects from the Upper Miocene Grubstake Formation of Alaska

摘要

Well-preserved insect wings are reported in weakly consolidated lacustrine shale from the Grubstake Formation, Upper Miocene of Suntrana Creek, central Alaska. 40Ar/39Ar dating of an immediately overlying volcanic ash indicates an age of slightly more than 6.7 ± 0.1 Ma, or approximately one million years before the opening of the Bering land bridge. The insects include four genera and two subfamilies of ants (Hymenoptera: Formicidae: Myrmicinae and Dolichoderinae), a species of Ichneumonidae (Hymenoptera), three genera and families of flies (Diptera: Chironomidae [genus indet.], Bibionidae [Bibio] and Lonchaeidae [Dasiops]), and the elytra of curculionid and carabid beetles. Extant distributions of the flies and possibly the ichneumonid include northerly latitudes around Suntrana. The ants are attributable to the extant genera Dolichoderus or Tapinoma (Dolichoderinae), Solenopsis or Erebomyrma (Myrmicinae), as well as Veromessor and Novomessor (Myrmicinae), indicating extensive biogeographic contraction to more southern latitudes of North America today. These finds are consistent with evidence from a slightly younger deposit from the uppermost Miocene (5.7 Ma) of the Seward Peninsula, Alaska. mplications are discussed regarding the differential effects of climate change and land bridges on the dispersal of various insect taxa.