A well-preserved fossil beetle assemblage of 70 taxa is described from a 10,000-yr-old sequence of lacustrine sediments on the Missouri Coteau, North Dakota. All of the 31 specifically determined taxa have been assigned to extant species, of which only 15 have been currently reported living in North Dakota. Many of the species are tree dwellers, some confined to spruce, thus indicating a woodland environment in contrast to the virtually treeless prairie of today.
There is apparently no region in North America where the species comprising the fossil assemblage are living together at present. Two-thirds of the species have been reported from woodland areas of southern Manitoba. Others, however, live mainly in eastern North America; one species is found in western North America.
Development of prairie about 9,000 to 8,500 yrs ago was probably responsible for the migration of the species within the fossil assemblage, although it is not clear why this should result in the widely separated distributions of many of the species at the present day.