Which one of the following is classified as a living fossil?

Ginkgo biloba is classified as a living fossil because it is the only surviving member of a group of trees known as Ginkgoales, which were abundant during the Mesozoic era, particularly the Jurassic period. These trees have remained relatively unchanged for millions of years, providing a direct link to ancient ecosystems. Ginkgo biloba has distinct characteristics, such as fan-shaped leaves and unique reproductive structures, that have persisted over time, highlighting its ancient lineage.

In contrast, while Sequoiadendron giganteum, Cycas revoluta, and Welwitschia mirabilis also have long histories and represent ancient lineages, they do not have the same level of continuity or direct lineage to their prehistoric forms as Ginkgo biloba. For example, Sequoiadendron giganteum represents a group of conifers that have evolved and diversified, Cycas revoluta is part of the cycads that have shown more variation over time, and Welwitschia mirabilis, though unique, is not the sole survivor of its lineage like Ginkgo. Thus, Ginkgo biloba stands out as a clear representative of ancient plant life that has survived largely unchanged, marking it as a quintessential living fossil.