[1][2][3] Through his research studying terrestrial vertebrate fossils he identified intervals of extinction in the Permian[4] and Triassic.
[5] He developed the concept of chronofauna, which he defined as "a geographically restricted, natural assemblage of interacting animal populations that has maintained its basic structure over a geologically significant period of time".
[6] He also proposed stratigraphic correlations between North American (especially the Chickasha and San Angelo Formations) and Russian vertebrate-bearing strata[4] for which additional support was found much later.
[7][8][9] The drop in terrestrial vertebrate diversity he proposed in at the end of the Kungurian stage of the Permian period that occurred 270 million years ago now carries his name - Olson's Extinction.
[2] University of California said that Olson "was an internationally recognized pioneer in studies of the origin and evolution of vertebrate animals".