Insects and Plant Macrofossils from Two Quaternary Exposures in the Old Crow-Porcupine Region, Yukon Territory, Canada

Abstract

Insect fossils and plant macrofossils have been recovered at two exposures in the Old Crow-Porcupine region (northern Yukon Territory). One assemblage of fossils, from an exposure on the Porcupine River in the Bluefish Basin, is probably about 32,400 years old, while the other, from an exposure in the Old Crow Basin, is older than 44,000 years.

Both assemblages seem to have been deposited when the sites from which they come were within a region of forest-tundra. The Porcupine River assemblage indicates that tree line along the middle Porcupine drainage during mid-Wisconsin time was significantly lower than at present. At that time more northern areas such as the Old Crow Basin would have been totally treeless in contrast with the forest-tundra vegetation there today.

The Old Crow assemblage probably represents climatic conditions as warm as at present. It includes fossils of one insect species and two plant species that do not occur today in the Old Crow Basin. The insect, a beetle (Micralymma brevilingue Schiødt), is now found farther north in a special type of tundra habitat. One of the plants, Alnus incana, may be absent today simply because of paucity of suitable habitat. The other, Najas flexilis, has a contemporary northern limit far to the south of the Yukon Territory. Because Najas does not grow in the Yukon Territory today, it is possible that its fossils imply warmer climate. However, such a conclusion is tempered by the further possibility that Najas is absent today not because of present climatic conditions but because of the severity of late Wisconsin climate in eastern Beringia (the Alaska-Yukon unglaciated refugium).