Alaskan Palaeogene insects: a challenge for a better knowledge of the Beringian 'route' (Odonata: Aeshnidae, Dysagrionidae)

摘要

Four 'routes', Beringian, De Geer, Thulean and Turgai Strait, are currently considered to explain Cenozoic continental interchanges between Eurasia and North America. These 'routes' had a crucial importance for vertebrates and insects. While vertebrates are not infrequent in these zones, there is very little direct evidence of insects to date the migrations and justify particular 'routes'. A 'route' is generally chosen on the basis of indirect evidence, such as molecular dating of clades. Alaska, on the Beringian 'route', is especially poor in fossil insects. Here we describe the first two Paleocene-Eocene insects from the Chickaloon Formation in Alaska, viz. Basiaeschna alaskaensis sp. nov., the first accurate fossil of this extant Nearctic aeshnid genus, and a representative of the extinct damselfly family Dysagrionidae, distributed in the Palaeogene of Eurasia and North America. These fossils provide direct evidence of the role of Beringia as a land bridge for insects during the Palaeogene. They are also evidence for a warm temperate climate in Alaska during this period of global warmth.