RECONSTRUCTING VEGETATION COVER IN DEEP TIME: PLANT MACROFOSSILS, POLLEN AND SPORES, OR BOTH?

Plant macrofossils and pollen and spores (sporomorphs) provide a record of ancient vegetation that is an important source of information about climate and biodiversity in the geological past. In many cases however, vegetation reconstructions are based on either plant macrofossils or sporomorphs alone. In such instances, interpretations may be limited by a lack of understanding of how accurately the fossil record of a particular plant, or group of plants, reflects the original standing vegetation. In an attempt to explore this issue, the relative representation of three botanical groups has been compared in the macrofossil and sporomorph fossil records. These groups are as follows: (1) Ferns, comprising all representatives of the Class Filicopsida; (2) Conifers and seed-ferns, comprising all representatives of the Class Coniferopsida and the Order Corystospermales; (3) Monosulcate producers, comprising all representatives of the Classes Cycadopsida, Ginkgopsida, Bennettitopsida and the Order Peltaspermales. Data are presented from a succession of fluvial–lacustrine rocks from a Triassic–Jurassic (c.200Ma) boundary section in east Greenland. Ferns appear relatively over-represented in the sporomorph record, whereas monosulcate producers appear relatively under-represented in the sporomorph record. Conifers and seed-ferns appear slightly over-represented in the sporomorph record, although mass occurrences of Stachyotaxus and Podozamites leaves result in considerable relative over-representation of conifers and seed-ferns in the macrofossil record at certain horizons. The results of this study indicate that vegetation reconstructions based on a single fossil group may be misleading, and should be interpreted with caution.