Palaeoproterozoic (2.2 Ga) life on land near Medicine Bow Peak, Wyoming, U.S.A.

Abstract

Tubular megafossils from the Palaeoproterozoic (ca. 2.3 Ga) Medicine Peak Quartzite of Wyoming have been regarded as possibly the earliest metazoan burrows. This interpretation has been controversial because these fossils are much older than accepted traces of metazoans. Additional similar specimens have now been found in palaeosols of the overlying Sugarloaf Quartzite (ca. 2.2 Ga), in the same area. These newly discovered fossils postdate fluvial deposition, predate metamorphic veining, and formed during oxidative, red, gypsic, soil formation. Oxidized tubular features lack regularity of width, backfills, scratches, or other complexities of metazoan trace fossils, and are more like cyanobacterial ropes, slime mold slugs, and fungal and lichen thalli of biological soil crusts. Because exact biological affinities are unknown, the fossils are assigned to palaeobotanical form taxa like many Precambrian fossils: Erythronema ramosum and E. robustum gen. et sp. nov. and Koilosolos pravus gen. et sp. nov. Such vertical, irregularly tubular fossils, which destroy prior bedding, are evidence of biological activity in Palaeoproterozoic palaeosols.