Insect Fossils from the Yukon

Abstract

Many Quaternary geological exposures in the Yukon have yielded identifiable insect fossils. All groups occurring in the Yukon today except Apterygota and the pterygote orders Ephemeroptera, Mecoptera, Orthoptera, Mallophaga, Anoplura, Thysanoptera and Siphonaptera have been recorded as fossils. Coleoptera dominate, with most beetle fossils being from the Carabidae, Staphylinidae, Curculionidae and sometimes Byrrhidae. For purposes of discussion the fossils from various sites are grouped according to age. One group includes Holocene and modern assemblages. Study of modern assemblages of insect fragments provides baseline informa- tion on taphonomy (the history of postmortal transportation and other events) and preservation. Some of the early Holocene faunas represent an intense warm period that occurred at high latitudes about 10 thousand years ago. A second group of fossil assemblages consists of those deposited during the coldest episode of the last glaciation when large areas of the Yukon were ice free and were part of East Beringia. Some of these samples support the conclusion drawn from plant and mammal fossils that the environment at the time was steppe-like, with no modern analogue. A third group is made up of fossils deposited between about 60 and 30 thousand years ago, an interval commonly called the mid-Wisconsinan. Some of the assemblages from this time period are very diverse; some contain unusual fossils, such as heads of noctuid moths and genital fragments of anthomyiid flies or other fossils that are exceptionally well preserved. The fourth group—interglacial faunas—includes only 2 sites. The one most accurately referred to the last interglacial (about 125 thousand years ago) contains a few taxa that do not occur as far north as the site today, including one beetle that now lives no farther north than Alberta. Such marked range extensions are more common in the fifth group of assemblages—those representing late Tertiary time. There are few assemblages of this age from the Yukon, but some are so close to the Yukon border that they represent the Tertiary fauna of the Yukon. Plant and insect fossils show that 3 million years ago rich coniferous forests covered at least all of central and northern Yukon and that the climate was less continental than at present. The insect fauna contained extinct species as well as some taxa now confined to the Palaearctic. The rich coniferous zone extended from eastern Siberia to Ellesmere Island and Greenland and was the last such forest connection across the Bering Straits. Subsequent intervals of dry land between Siberia and Alaska were charac- terized by severe arctic conditions and no forests. Resume. Insectes fossiles du Yukon. Plusieurs fouilles geologiques a des sites du Quaternaire au Yukon ont revele la presence d'insectes fossiles identifiables. Des fossiles de tous les groupes actuels d'insectes du Yukon ont ete trouves, a l'exception des Apterygotes et de quelques ordres pterygotes, Ephemeroptera, Mecoptera, Orthoptera, Mallophaga, Anoplura, Thysanoptera et Siphonaptera. Les coleopteres dominent et la plupart des fossiles de cet ordre appartiennent aux familles Carabidae, Staphylinidae, Curculionidae et parfois Byrrhidae. Pour des raisons d'ordre logistique, les fossiles des differents sites sont regroupes en fonction de l'epoque. Un