Gregory John Retallack (born 8 November 1951) is an Australian paleontologist, geologist, and author who specializes in the study of fossil soils (paleopedology).

His research has examined the fossil record of soils though major events in Earth history, extending back some 4.6 billion years.

He was a professor in the Department of Geological Sciences since 1992, and Director of the Condon Collection of the University of Oregon Museum of Natural and Cultural History since 2009.

[citation needed] A fossil collector since the age of 6, Retallack was outspoken concerning federal seizure in 1993 of Sue (dinosaur) the skeleton of Tyrannosaurus rex excavated by Pete Larson.

[7] Later construction of Cenozoic paleoclimate time series led to the idea that grassland-grazer coevolution was responsible for climatic cooling over the past 50 million years,[8] which has implications for biosequestration of carbon.

Fieldwork in Kenya on paleosols associated with apes (Proconsulidae) ancestral to humans revealed that the evolutionary transition to upright stance occurred in woodlands rather than savannas.

[9] Paleosols of the Cretaceous-Paleogene boundary in Montana implicated abrupt paleoclimatic change and acid rain from extraterrestrial impact in the extinction of dinosaurs[10] Work on the Permian-Triassic boundary in Antarctica lead to formulation of an hypothesis of greenhouse crisis due to methane outburst associated with flood basalt in this greatest of all mass extinctions[11] Devonian fossil soils at sites for tetrapods suggest a woodland hypothesis for the evolutionary transition from fish to amphibian.

[18] Retallack's work on Late Permian mass extinction[11] was featured on several television documentaries, including the BBC's The Day The Earth Nearly Died[20] and Science Channel USA's Miracle Planet episode "Death and Rebirth".

[34] Retallack also developed new techniques in cuticle analysis for using stomatal index of fossil Ginkgo leaves to obtain past atmospheric carbon dioxide.

[35] This work led Retallack to propose the concept of paleoenvironmental regulation by the Proserpina Principle: plants cool the planet, whereas animals warm it.