What are disharmonious animal associations in late Pleistocene fossil sites?

In late Pleistocene fossil sites, disharmonious animal associations refer to the coexistence of species that are presently allopatric—meaning they are currently separated by hundreds to thousands of kilometers or significant differences in elevation—and are presumed to be ecologically incompatible.1

These assemblages often feature temperate and Arctic forms occurring together, a phenomenon that lacks a modern analogue. The presence of these associations suggests that the late Pleistocene climate was more equable than that of the present day, characterized by reduced seasonal extremes in temperature and moisture.21

During this period, the influence of ice sheets likely moderated winter temperatures by blocking Arctic air masses, while simultaneously keeping summers cooler. Consequently, plants and animals whose modern geographic ranges are restricted by extreme seasonal heat or cold were able to coexist. The transition to modern biotic communities appears to have resulted from complex biological and biophysical interactions as these equable conditions gave way to the more variable climates of the Holocene.21