PhD: Filling the early Tonian gap in the fossil record of complex life

Overview
Take a look at the life around you and you’ll see a world full of complex eukaryotes (including ourselves). However, life on Earth didn’t always have this array of morphological complexity. Understanding when and why complex eukaryotes first diversified is a fundamental question in the history of life on our planet. Genetic and fossil data suggest that eukaryotes first evolved over 1,600 million years ago but didn’t diversify or become ecologically significant until just prior to the Cambrian Explosion, 700–600 million years ago. Why is there such a significant lag time between when complex life arose and diversified? Was the lag a consequence of the difficulty in acquiring biological machinery or a function of constraints based on the habitat into which these organisms evolved? This project will grapple with some of these most fundamental questions about life on our planet.

Methodology
Fossils placed in geological context provide a means to directly ask when eukaryotes diversified, and to test correlations to environmental changes which may have acted as evolutionary drivers. However, prior to the Phanerozoic adoption of biomineralisation, we are reliant on unusual sedimentary conditions that fossilised decay-prone organisms. Consequently, fossils that describe the rise of complex life are rare. In fact, the fossil record of early eukaryotes that can be allied to modern groups, with the exception of one fossil species, is younger than 800 million years old, much younger than genetic estimates for their ages.

The relatively unexplored ~900 million-year-old Veteranen Group of Svalbard, therefore, contains sedimentary rocks of the right age to fill a critical gap in our understanding of early eukaryotic evolution. Although preliminary studies showed its strata to be fossiliferous, much of the stratigraphy remains unexplored (Knoll 1982, Knoll and Swett 1985). Adjacent strata have proved some of the most fossiliferous in the Proterozoic Eon (Butterfield et al. 1994), emphasising the potential of the Veteranen Group for new discoveries.

This DPhil will focus on the palaeontology of the succession, revealing new fossils that will give an insight onto the nascent eukaryotic world. Existing collaborations with geologists at Dartmouth and Yale universities will provide a wealth of geological information on the contextual palaeoenvironment. This will allow hypotheses relating Tonian environmental changes and early eukaryotic evolution to be tested.

Timeline
Year 1: Training in geochemical methods such as XRD, and in fossil extraction and identification. Sample acquisition and mineralogical analyses to determine horizons best suited to fossil preservation.
Years 2 and 3: Sample analysis via fossil extraction and examination.
Year 4: Data integration, thesis completion, papers for international journals/conference presentation.

Training & Skills
This project will provide the student with an interdisciplinary skillset in sedimentary geology and palaeontology. A significant portion of the project will be lab-based, where the primary skills acquired will by those of microfossil extraction and examination. The student will also become familiar with the use of a raft of state-of-the-art geochemical techniques currently employed in geobiology (e.g., XRD, SEM-EDS). The supervisor has recently shown that sediments most conducive to the fossilisation of non-mineralised organisms have a mineralogical signature (Anderson et al. 2018). This mineralogical signature provides a vital new toolkit for identifying those sedimentary horizons most likely to preserve these rare early fossils. Fieldwork in Svalbard is also possible subject to funding, and the student would be encouraged to present their research at major international conferences (e.g., PalAss, GSA).

References & Further Reading
R.P. Anderson, N.J. Tosca, R.R. Gaines, N. Mongiardino-Koch, and D.E.G. Briggs, A mineralogical signature for Burgess Shale-type fossilisation. Geology 46 (2018) 347–350.
N.J. Butterfield, Early evolution of the Eukaryota. Palaeontology 58 (2015) 5–17.
N.J. Butterfield, K. Swett, and A.H. Knoll, Paleobiology of the Neoproterozoic Svanbergfjellet Formation, Spitsbergen. Fossils and Strata 34 (1994) 1–84.
P.A. Cohen and F.A. Macdonald, The Proterozoic record of eukaryotes. Paleobiology 41 (2015) 610– 632.
A.H. Knoll, Microfossil-based biostratigraphy of the Precambrian Hecla Hoek sequence, Nordauslandet, Svalbard. Geological Magazine 119 (1982) 269–279.
A.H. Knoll, Paleobiological perspectives on early eukaryotic evolution. Cold Spring Harbor Perspectives in Biology 6 (2014) a016121
A.H. Knoll and K. Swett, Micropalaeontology of the Late Proterozoic Veteranen Group, Spitsbergen. Palaeontology 28 (1985) 451–473.