The remains of organisms from past geological ages preserved in sedimentary rocks either as actual structures or as impressions, casts, or moulds. Plant fossils are rarely as well preserved as animal fossils because their tissues do not normally contain calcified structures. They are usually therefore completely decomposed before the processes of fossilization, including carbonization and petrification, act to preserve them. The remains of macroscopic structures, such as branches, leaves, fruits, and seeds, are termed megafossils while those of pollen and spores are called microfossils. If a fossil cannot be assigned to any genera containing extant species then its genus is termed an organ genus. Similarly if it cannot be assigned to a family it is Placed in a form genus. The study of fossils has helped in the construction of phylogenetic classification schemes and has also thrown light on how some of the complex structures of extant plants have evolved. See also palaeontology. |
