2011 Annual Science Report
Massachusetts Institute of Technology Reporting | SEP 2010 – AUG 2011
Protists of the Neoproterozoic
T. Bosak (MIT), S. Pruss (Smith College), F. Macdonald (Harvard U.) and D. Lahr (U. Sao Paolo) discovered fossils of microscopic eukaryotes in limestone and dolostone strata deposited between the two Neoproterozoic low-latitude glaciations (between ~ 716 and 635 million years ago). These fossils include amoeba-like organisms that incorporated mineral-rich particles from the environment into their shells, mineral-rich shells of the oldest putative foraminiferans, and thick flask-shaped organic envelopes of the first putative ciliates, representatives of a major group of modern eukaryotes. These fossils demonstrate a previously unrecognized record of body fossils during the ~ 70 million years between the two “Snowball Earth” episodes and document the increasing diversity of morphologically and compositionally modern eukaryotes before the rise of complex animals.
T. Bosak (MIT), S. Pruss (Smith College), F. Macdonald (Harvard U.), D. Lahr (U. Sao Paolo) and E. Matys (MIT) recently discovered eukaryotic tests in stratigraphically unambiguous ~715-635 Ma strata. The fossil tests from the Rasthof Formation (Pruss et al., 2010) share compositional and morphological similarities with modern agglutinated lobose testate amoebae (Bosak et al., 2011), and agglutinated single-chambered foraminifera (Bosak et al., in press a). At present, this is the first known occurrence of widespread agglutination in the fossil record and the first occurrence of putative foraminiferans. Examination of less thermally altered strata deposited between ~715 and 635 Ma from Mongolia lead to the discovery of organic tests of the first putative ciliates (Bosak et al., in press b) and other remnants of fossil eukaryotes that are currently being investigated. The presence of phagotrophic eukaryotes capable of building recalcitrant organic and/or mineral-rich tests before 635 Ma attests to the increasingly complex trophic structure of the oceans during this time. This may have fundamentally changed the cycling of particulate and dissolved organic carbon in oceans, driving an increase in atmospheric oxygen and the subsequent radiation of metazoans.
Bosak, T., Lahr D.J.G., Pruss, S.B., Macdonald, F.A., Gooday, A.J., Dalton, L., and E.D. Matys, Possible early foraminiferans in post-Sturtian cap carbonates, Geology, in press.
Bosak, T., Lahr, D., Macdonald, F.A, and E.D. Matys, Putative Cryogenian ciliates from Mongolia, Geology, in press.
Bosak, T., Lahr, D., Pruss, S. B., Macdonald, F. A., Dalton, L., and E.D. Matys (2011) Agglutinated tests in post-Sturtian cap carbonates from Namibia and Mongolia, Earth and Planetary Science Letters, 308: 29-40.
Pruss, S.B., Bosak, T., Macdonald, F.A., McLane, M., and P.F. Hoffman (2010) Microbial facies in a Sturtian cap carbonate, the Rasthof Formation, Otavi Group, northern Namibia, Precambrian Research, 181: 187-198.
PROJECT MEMBERS:Tanja Bosak
RELATED OBJECTIVES:Objective 4.1
Earth's early biosphere.
Production of complex life.
Co-evolution of microbial communities
Effects of environmental changes on microbial ecosystems