Ginkgo, Ginkgo biloba
Ginkgoes are a very old line of plants, their earliest representatives being found in rocks of Permian age some 280 million years old. At times in the geologic past they have been widespread and abundant, and the dinosaurs surely fed upon them. The fossil species Ginkgo adiantoides, indistinguishable from the modern ginkgo, is found in rocks as old as Early Cretaceous (140 to 100 million years ago), which appears to have been the ginkgo's heyday.
Fossils of ginkgo species are found throughout the northern hemisphere in rocks dating from Jurassic to Miocene times. They disappear from North America by the Pliocene and vanish from Europe by the Pleistocene.
The ginkgo tree is well-known today as a street tree and ornamental tree, but for centuries it appears to have been extinct in the wild. Only cultivated trees survived, in Buddhist monasteries in China, until they were planted across Asia starting about a thousand years ago.
Dawn Redwood, Metasequoia glyptostroboides
The dawn redwood is a conifer that sheds its leaves every year, unlike its cousins the coast redwood and giant sequoia. Fossils of closely related species date from late in the Cretaceous and occur all over the northern hemisphere. Their most famous locality is probably on Axel Heiberg Island in the Canadian Arctic, where stumps and leaves of Metasequoia sit still unmineralized from the warm Eocene Epoch some 45 million years ago.
The fossil species Metasequoia glyptostroboides was first described in 1941. Its fossils were known before that, but they were confused with those of the true redwood genus Sequoia and the swamp cypress genus Taxodium for more than a century. M. glyptostroboides was thought to be long extinct. The latest fossils, from Japan, dated from the early Pleistocene (2 million years ago). But a living specimen in China was found a few years later, and now this critically endangered species is thriving in the horticultural trade. Only about 5000 wild trees remain.
Recently, Chinese researchers described a single isolated specimen in Hunan province whose leaf cuticle differs from all other dawn redwoods and exactly resembles the fossil species. They suggest that this tree is truly the living fossil and that the other dawn redwoods have evolved from it by mutation. The science, along with much human detail, is presented by Qin Leng in a recent issue of Arnoldia. Qin also reports vigorous conservation efforts in China's "Metasequoia Valley."
Wollemi Pine, Wollemia nobilis
The ancient conifers of the southern hemisphere are in the araucaria plant family, named for the Arauco region of Chile where the monkey-puzzle tree (Araucaria araucana) lives. It has 41 species today (including the Norfolk Island pine, kauri pine and bunya-bunya), all of them scattered among the continental fragments of Gondwana: South America, Australia, New Guinea, New Zealand and New Caledonia. But ancient araucarians forested the globe in Jurassic times.
In late 1994, a ranger in Australia's Wollemi National Park in the Blue Hills found a strange tree in a small, remote canyon. It was found to match fossil leaves going back 120 million years in Australia. Its pollen grains were an exact match to the fossil pollen species Dilwynites, found in Antarctica, Australia and New Zealand in rocks as old as Jurassic. The Wollemi pine is known in three small groves, and all specimens today are as genetically alike as twins.
Hard-core gardeners and plant fanciers are very interested in the Wollemi pine, not just for its rarity but because it has beautiful foliage. Look for it at your local progressive arboretum.
Why "Living Fossil" Is a Poor Term
The name "living fossil" is unfortunate in some ways. The dawn redwood and Wollemi pine present the best case for the term: recent fossils that appear identical, not just similar, to a living representative. And the survivors were so few that we may not have enough genetic information to explore their evolutionary history in depth. But most "living fossils" don't match that story.
The type of plant called the cycad is an example that used to be in the textbooks (and may still be). In yards and gardens, the typical cycad is the sago palm, and it had supposedly been unchanged since Paleozoic time. But today there are about 300 species of cycad, and genetic studies show that most are only a few million years old.
But beyond genetics, most "living fossil" species differ in small details from today's species: shell ornamentation, numbers of teeth, configuration of bones and joints. Although the line of organisms had a stable body plan that succeeded in a certain habitat and lifeway, its evolution never stopped. The idea that the species became evolutionarily "stuck" is the main thing wrong about the notion of "living fossils."
There is a similar term used by paleontologists for fossil types that disappear from the rock record, sometimes for millions of years, and then appear again: Lazarus taxa, named for the man that Jesus raised from the dead. A Lazarus taxon is not literally the same species, found in rocks millions of years apart. "Taxon" refers to any level of taxonomy, from the species through the genus and family up to the kingdom. The typical Lazarus taxon is a genusa group of speciesso that matches what we now understand about "living fossils."