Complex animals first evolved during the Ediacaran period, between 635 and 542 million years ago, when the oceans were just becoming fully oxygenated. In situ fossils of the mobile forms of these animals are associated with microbial sedimentary structures1, 2, 3, and the animal’s trace fossils generally were formed parallel to the surface of the seabed, at or below the sediment–water interface4, 5. This evidence suggests the earliest mobile animals inhabited settings with high microbial populations, and may have mined microbially bound sediments for food resources6, 7, 8. Here we report the association of mobile animals—insect larvae, oligochaetes and burrowing shore crabs—with microbial mats in a modern hypersaline lagoon in Venezuela. The lagoon is characterized by low concentrations of dissolved O2 and pervasive biomats dominated by oxygen-producing cyanobacteria, both analogous to conditions during the Ediacaran. We find that, during the day, O2 levels in the biomats are four times higher than in the overlying water column. We therefore conclude that the animals harvest both food and O2 from the biomats. In doing so, the animals produce horizontal burrows similar to those found in Ediacaran-aged rocks. We suggest that early mobile animals may have evolved in similar environments during the Ediacaran, effectively exploiting oases rich in O2 that formed within low oxygen settings.
At a glance
- Assemblage palaeoecology of the Ediacara biota: The unabridged edition?. Palaeogeogr. Palaeoclimatol. Palaeoecol. 232, 131–147 (2006). , &
- 157–179 (Special Publications Vol. 286, Geological Society, 2007). , & in The Rise and Fall of the Ediacaran Biota
- Textured organic surfaces associated with the Ediacara biota in South Australia. Earth Sci. Rev. 96, 196–206 (2009). &
- Trace fossil preservation and the early evolution of animals. Palaeogeogr. Palaeoclimatol. Palaeoecol. 220, 19–29 (2005). , &
- A critical look at the Ediacaran trace fossil record. Top. Geobiol. 27, 115–157 (2006). , &
- 97–105 (Bibliotheks und Informationssystem der Universität Oldenburg, 1994). & in Biostabilization of Sediments (eds Krumbein, W., Paterson, D. M. & Stal, L. J.)
- Microbial mats in terminal Proterozoic siliciclastics; Ediacaran death masks. Palaios 14, 40–57 (1999).
- Trace fossils in the Ediacaran–Cambrian transition: Behavioural diversification, ecological turnover and environmental shift. Palaeogeogr. Palaeoclimatol. Palaeoecol. 227, 323–356 (2005). , &
- Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies. Nature 382, 127–132 (1996). &
- Late-Neoproterozoic deep-ocean oxygenation and the rise of animal life. Science 315, 92–95 (2007). , &
- Biogeochemical cycles of carbon, sulfur, and free oxygen in a microbial mat. Geochim. Cosmochim. Acta 57, 3971–3984 (1993). &
- Age of Neoproterozoic bilatarian body and trace fossils, White Sea, Russia: implications for metazoan evolution. Science 288, 841–845 (2000). et al.
- First evidence for locomotion in the Ediacara biota from the 565 ma Mistaken Point Formation, Newfoundland. Geology 38, 123–126 (2010). , &
- Taphonomy of the Terminal Proterozoic Ediacara Biota, South Australia. Doctoral, Univ. of California at Los Angeles, Univ. Microfilms (1996).
- The origin of the Metazoa in the light of the Proterozoic fossil record. Paleontol. Res. 7, 9–41 (2003). &
- Early molluscan evolution: evidence from the trace fossil record. Palaios 25, 565–575 (2010). &
- Biomat-related lifestyles in the Precambrian. Palaios 14, 86–93 (1999).
- Complex trace fossils from the terminal Proterozoic of Namibia. Geology 28, 143–146 (2000). , , &
- Background to the Cambrian explosion. J. Geol. Soc. 149, 585–587 (1992).
- The impact of bioturbation on infaunal ecology and evolution during the Proterozoic–Cambrian transition. Palaios 14, 58–72 (1999). &
- Resistance to anoxia of Chironomus plumosus and Chironomus anthracinus (Diptera) larvae. Ecography 1, 333–336 (1978). &
- Chemoreception, odor landscapes, and foraging in ancient marine landscapes. Palaeontol. Electron. 10, 11 (2007).
- Concentration and transport of nitrate by the mat-forming sulphur bacterium Thioploca. Nature 374, 713–715 (2002). et al.
- The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records. Phil. Trans. R. Soc. B 363, 1435–1443 (2008). , , &
- Matground structures and redox facies. Palaios 14, 25–39 (1999).
- Kinneyia-type wrinkle structures—critical review and model of formation. Palaios 23, 65–77 (2008). , &
- Supplementary Information (800KB)