<p>The Early Paleozoic, specifically the Middle Ordovician, marks a significant period in Earth's history due to the appearance and diversification of life on land. Plant megafossil records indicate vascular plants first appeared in the Early Silurian and by Devonian times had diversified rapidly (e.g. Wellman and Gray, 2000; Steemans et al., 2009; Kenrick et al., 2012; Strother, 2016). However non-vascular plants (bryophytes) predating vascular plants are rarely preserved as body fossils and the bryophyte microfossil record in the lowermost Palaeozoic is scarce. This lack of fossil data severely limits our understanding of life in the earliest non-marine environments and the origin of land plants.

<p>In comparison to microfossils, molecular fossils (biomarkers) are more ubiquitous in the sedimentary record and have a higher preservation potential, thus providing a powerful tool to track terrestrial signals when microfossils are either scarce or absent. Molecular proxies such as long chain n-alkanes have been used extensively in both modern and ancient environments to identify terrestrial contributions to the organic matter (e.g. Eglinton and Hamilton, 1967; Ficken et al., 2000; Hautevelle et al., 2006). Furthermore, the isotopic composition of these molecules can be used to further distinguish between sources (e.g. Bird et al., 1995; Sikes et al., 2009; Rouillard et al., 2016). That being said, only relatively few studies have combined palynological evidence with geochemical proxies to assess geochemical signatures of early land plants.

<p>This work presents biomarker and palynological data of the Middle Ordovicianupper Goldwyer Formation which records the earliest occurrence of land plant microfossils (cryptospores) in Australia. The higher-molecular-weight n-alkane distributions and their isotopic compositions recorded in the upper Goldwyer show high resemblances to modern day bryophytes and aquatic macrophytes. Retene, a biomarker conventionally used as a proxy for gymnosperms, was also identified in some extracts. The presence of retene in Middle Ordovician (this work) and Silurian (Romero-Sarmiento et al., 2010) rocks indicates conifers are not the sole source of this compound.

<p>Linking biomarkers and palynology has shown to beuseful in the study of early land plants where fossil records are sparse. Molecular and isotopic proxies distinctive of these plants can provide a more complete record of the geographical distribution of early land plants, providing useful information to understand their early evolution.

<p>Bird, M.I., Summons, R.E., Gagan, M.K., Roksandic, Z., Dowling, L., Head, J., Fifield, L.K., Cresswell, R.G., Johnson, D.P., 1995. Terrestrial vegetation change inferred from n-alkane δ13C analysis in the marine environment. Geochimica et Cosmochimica Acta 59, 2853-2857.

<p>Eglinton, G., Hamilton, R.J., 1967. Leaf epicuticular waxes. Science 156, 1322-1335.

<p>Ficken, K.J., Li, B., Swain, D.L., Eglinton, G., 2000. An n-alkane proxy for the sedimentary input of submerged/floating freshwater aquatic macrophytes. Organic Geochemistry 31, 745-749.

<p>Hautevelle, Y., Michels, R., Malartre, F., Trouiller, A., 2006. Vascular plant biomarkers as proxies for palaeoflora and palaeoclimatic changes at the Dogger/Malm transition of the Paris Basin (France). Organic Geochemistry 37, 610-625.

<p>Kenrick, P., Wellman, C.H., Schneider, H., Edgecombe, G.D., 2012. A timeline for terrestrialization : consequences for the carbon cycle in the Palaeozoic. Philosophical Transactions of the Royal Society B: Biological Sciences 367, 519-536.

<p>Romero-Sarmiento, M.F., Riboulleau, A., Vecoli, M., Versteegh, G.J.M., 2010. Occurrence of retene in upper Silurian-lower Devonian sediments from North Africa: origin and implications. Organic Geochemistry 41, 302-306.

<p>Rouillard, A., Greenwood, P.F., Grice, K., Skrzypek, G., Dogramaci, S., Turney, C., Grierson, P.F., 2016. Interpreting vegetation change in tropical arid ecosystems from sediment molecular fossils and their stable isotope compositions: a baseline study from the Pilbara region of northwest Australia. Palaeogeography, Palaeoclimatology, Palaeoecology 459, 495-507.

<p>Sikes, E.L., Uhle, M.E., Nodder, S.D., Howard, M.E., 2009. Sources of organic matter in a coastal marine environment: Evidence from n-alkanes and their delta13C distributions in the Hauraki Gulf, New Zealand. Marine Chemistry 113, 149-163.

<p>Steemans, P., Herisse, A. Le, Melvin, J., Miller, M. a, Paris, F., Verniers, J., Wellman, C.H., 2009. Origin and radiation of the earliest vascular land plants. Science (New York, N.Y.) 324, 353.

<p>Strother, P.K., 2016. Systematics and evolutionary significance of some new cryptospores from the Cambrian of eastern Tennessee, USA. Review of Palaeobotany and Palynology 227, 28-41.

<p>Wellman, C.H., Gray, J., 2000. The microfossil record of early land plants. Philosophical Transactions of the Royal Society B: Biological Sciences 355, 717-732.