Gregory Retallack

Gregory John Retallack (born 8 November 1951) is an Australian paleontologist, geologist, and author who specializes in the study of fossil soils (paleopedology). He is a professor emeritus at University of Oregon and his research is primarily concerned with the fossil record of soils though Earth history.^[1] His research has included investigations into climate change, the extinction of dinosaurs, the origins of upright walking humans. One aspect of his career that has been controversial is the supposed terrestrial nature of Ediacaran fossils. He has written two well-received textbooks on paleopedology, and has appeared in numerous media shows.^[2]

Gregory Retallack
Greg Retallack, near Suplee, central Oregon, 1982
Born	(1951-11-08) 8 November 1951 (age 74) Hobart, Tasmania
Citizenship	American and Australian
Alma mater	Macquarie University, University of New England (Australia)
Known for	Paleopedology
Spouse(s)	Diane Retallack, Director Eugene Concert Choir
Scientific career
Thesis	A biostratigraphy for terrestrial Triassic rocks of Gondwanaland  (1978)
Doctoral advisor	Rodney E. Gould
Website	https://blogs.uoregon.edu/gregr/

Biography

Retallack moved with his family from Hobart, Tasmania to suburban Sydney at age 4.^[3] He grew up in Hurstville and then Epping. He attended The King's School, Parramatta, then studied biology and paleontology at Macquarie University. He received a BSc Hons with University Medal in 1974 from the University of New England (Australia) and a PhD in 1978 in geology from the same university. After a postdoctoral fellowship at Indiana University Bloomington he joined the faculty at the University of Oregon in 1981. 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. Since retirement in 2022 he has been a professor emeritus.^{[citation needed]}

Retallack on Mount Cook, New Zealand, 1974

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.^[4]

Work

Evolution of life on land

Oligocene fossil soils of well-drained woodlands (red bands) and swamps (black spots) in the Painted Hills, Oregon^[5]

Retallack's research focuses on the study of paleosols (fossilized soils) to reconstruct ancient environments. In 1973, he proposed that paleosols preserved beneath fossil plant horizons could provide data on ancient plant communities that plant fossils alone could not reveal.^[6][7] He has applied this approach to various stages of evolutionary history, offering hypotheses that sometimes challenge established scientific understanding.^[8]

Research findings

Retallack has used paleosols to investigate several major extinction and evolutionary events. Regarding climate change, he argued that the coevolution of grasslands and grazers over the past 50 million years drove global cooling via carbon biosequestration.^[9][10] In the field of human evolution, Retallack's fieldwork in Kenya concerning Proconsulidae (primates ancestral to humans) led him to suggest that the evolutionary transition to an upright stance occurred in woodland environments rather than in open savannas.^[11]

He has also applied this methodology to mass extinction events. Studying the Cretaceous-Paleogene boundary in Montana, he hypothesized that acid rain resulting from an extraterrestrial impact contributed to the extinction of dinosaurs.^[12] Similarly, his work in Antarctica on the Permian-Triassic boundary led to the hypothesis that the mass extinction was driven by a greenhouse gas crisis caused by methane released from coal instructions during massive volcanic events (flood basalts).^[13] Furthermore, he has proposed a "woodland hypothesis" regarding the Devonian transition of vertebrates from fish to amphibians.^[14]

In 2013, Retallack identified problematic fossils in Paleoproterozoic paleosols from South Africa, which he named Diskagma. He identified the species as a fungus comparable to the living Geosiphon.^[15] Dated to 2.2 billion years old, these fossils would push back the record of life on land significantly from the previously accepted record of 1.2 billion years.^[16][17]

Media appearances

Retallack's work has been featured in several documentaries and science programs. His research on the Late Permian extinction appeared in the BBC's The Day the Earth Nearly Died^[18] and the Science Channel's Miracle Planet.^[19] Additionally, an episode of Prehistoric Predators on the National Geographic Channel covered his work on the Miocene of Panama.^[20][21] His findings regarding early life on land^[22] were also discussed on radio programs broadcast by National Public Radio,^[23] the Canadian Broadcast Corporation,^[24] and Oregon Public Broadcasting.^[25]

Paleosols (massive red bands) at horizons for Ediacaran fossils in Brachina Gorge, South Australia.^[22]

Scientific controversies

Retallack's work interpreting the Avalon and White Sea assemblages of the Ediacaran biota as lichens^[26] has been refuted.^[27] His proposal that Ediacaran fossils were preserved in subaerial paleosols, and thus not marine fossils,^[22][2] has been supported by a minority of researchers^[28] but dismissed by other paleontologists.^[29][30][31] Nature called it a "controversial claim" in a news report, in which paleontologist Guy Narbonne said "[I]t quickly became clear that there are simpler explanations for the features Retallack had validly noted, and most of us moved on to more promising explanations."^[32] Retallack continues to maintain his position.^[33][34]

In 2020, Retallack and other researchers claimed to have found Dickinsonia fossils from Bhimbetka rock shelters, India.^[35] However, in 2023 other researchers believed the material was actually the decayed remnants of a beehive.^[36]

Boards

Retallack has served as an associate or technical editor for such scientific journals as Geology, PALAIOS, and Journal of Sedimentary Research. His fellowships include the Geological Society of America, and the American Association for the Advancement of Science.

He served as the president and vice president of the Cordilleran Section of the Paleontological Society, of the Oregon Academy of Sciences,^[37] and of the University of Oregon Chapter of the Society of Sigma Xi.

Critical reception

Of Soils of the Past, David Fastovsky concludes "it is requisite for all persons trying to understand paleosols".^[38] Of A Colour Guide to Paleosols, Daniel Yaalon concludes "Highly recommended for students and researchers alike for an introductory insight to paleopedology and to whet and refine their skills in paleosol interpretation."^[39] Both reviews however baulked at the unfamiliarity of soil science terminology and classification in these texts.^[38][39]

Retallack's approach to the description and interpretation of paleosols has been widely adopted.^[40] Some controversy concerned use of modern soil taxonomies for paleosols,^[41] but Retallack's approach has since been validated by development of additional geochemical proxies for soil taxonomic criteria.^[42] Retallack's confirmation of abrupt paleoenvironmental change on land at the Cretaceous-Tertiary^[12] and Permian-Triassic boundaries,^[13] has been supported by later research on extinction.^{[citation needed]}

Awards and honors

Retallack has been honored for his research, including the Stillwell Award of the Geological Society of Australia, for best paper in the society journal in 1977, Ingerson Award of the Geochemical Society in 2015, and the Antarctica Service Medal of the U.S. National Science Foundation in 1999.^{[citation needed]} He has been an invited lecturer throughout the U.S., and also to Germany, England, China, Thailand and India.

Bibliography

Textbooks

• Soils of the past: an introduction to paleopedology, 3rd edition, Wiley, Chichester, 2019, ISBN 978-1-119-53040-4
• A colour guide to paleosols, John Wiley and Sons, Chichester, 1997, ISBN 0-471-96711-4
• Soil grown tall: the epic saga of life from earth, Springer Nature, Cham, Switzerland, 2022, ISBN 978-3-030-88738-4

Selected publications

• Retallack, G. J.; Feakes, C. R. (1987). "Trace fossil evidence for Late Ordovician animals on land". Science. 235 (4784): 61–63. Bibcode:1987Sci...235...61R. doi:10.1126/science.235.4784.61. PMID 17769314. S2CID 37351505.
• Retallack, G. J.; Dugas, D. P.; Bestland, A. E. (1990). "Fossil soils and grasses of the earliest East African grasslands". Science. 247 (4948): 1325–1328. doi:10.1126/science.247.4948.1325. PMID 17843796. S2CID 46233081.
• Retallack, G. J.; Germán-Heins, J. (1994). "Evidence from paleosols for the geological antiquity of rain forest". Science. 265 (5171): 499–502. Bibcode:1994Sci...265..499R. doi:10.1126/science.265.5171.499. PMID 17781308. S2CID 44497635.
• Retallack, G. J. (1995). "Permian-Triassic life crisis on land". Science. 267 (5194): 77–80. Bibcode:1995Sci...267...77R. doi:10.1126/science.267.5194.77. PMID 17840061. S2CID 42308183.
• Retallack, G. J. (1997). "Early forest soils and their role in Devonian global change". Science. 276 (5312): 583–585. doi:10.1126/science.276.5312.583. PMID 9110975.
• Retallack, G. J. (2001). "A 300 million year record of atmospheric carbon dioxide from fossil plant cuticles". Nature. 411 (6835): 287–290. Bibcode:2001Natur.411..287R. doi:10.1038/35077041. PMID 11357126. S2CID 4430851.
• Retallack, G. J. (2008). "Rocks, views, soils and plants at the temples of ancient Greece". Antiquity. 82 (317): 640–657. doi:10.1017/s0003598x00097283. S2CID 15115738.
• Retallack, G. J. (2013). "Ediacaran life on land". Nature. 493 (7430): 89–92. Bibcode:2013Natur.493...89R. doi:10.1038/nature11777. PMID 23235827. S2CID 205232092.