Extant Plants

Extant Plants

The term “living fossil” was coined by Charles Darwin to describe plants still surviving today that were known to be thriving millions of years ago. Primitive spore and seed-bearing plants which flourished in the ages of the dinosaurs are still found on earth today. When dinosaurs roamed the planet, 65-225 million years ago,  was a very different place; climate, vegetation, even continental spacial positioning and topography all vastly differed from what we know now. The forest understory was dominated by pteridophytes, spore-bearing plants, such as ferns, horsetails and club mosses. The majority of plants identified from this period exist as fossilized imprints of leaves in sedimentary rock or petrified plant tissue, the sporangia and strobili can be matched with currently living representatives. Although only a few genera remain, they are very recognizable, and successful.

 

Equisetum, horsetails, is one of the few remaining genera termed a living fossil. Members of this genus can be directly linked to their ancient ancestors.

Equisetum, horsetails, is one of the few remaining genera termed a living fossil. Members of this genus can be directly linked to their ancient ancestors.

Seed-bearing plants, spermatophytes, developed during the 150 million year period when dinosaurs ruled the planet. They quickly became the dominant vegetation on earth, most conspicuously seed ferns, cycads and conifers, which are gymnosperm, “naked sperm”. These plants, so-called for their seeds not being enclosed in fruits like those of flowering plants, are deserving of the title living fossils, none so much as the Gingko biloba (featured above). The fossil record is littered with examples of this plant’s ancestors imprinted into sedimentary rock dating back to the Jurassic and Triassic periods, 135-210 million years ago. The leaf shape strongly resembles individual leaflets on the maidenhair fern. Earlier in the century petrified Gingko beckii logs were discovered trapped in sediments formed by lava flows near the Columbia River in Washington. While Gingko trees are still planted in the landscape all living specimens are descended from a variety developed in Asia, though there was a time, 30 million years ago, when they formed dense, vast forests across the continent.

Another example of a living fossil which remains in our landscapes today is the dawn redwood, Metasequoia glyptostroboides. First described from fossil material by Japanese paleobotanist Shigeru Miki in 1941, the dawn redwood was thought to be extinct but was then found growing in a remote valley in central China. Fossils, leaf imprints and petrified wood, of ancestral Metasequoia species have been found in North America in deposits from the Cretaceous period. Some of these fossils have been dated back to 90 million years ago, when the climate was much warmer and more humid. The dawn redwood superficially resembles the California coastal redwood, Sequoia sempervirens, hence the name Metasequoia.

The leaves and cones if the dawn redwood strongly resemble those of the California coastal redwood.

The leaves and cones if the dawn redwood strongly resemble those of the California coastal redwood.

Cycads were so successful during the Mesozoic era it is often called the “Age of Cycads and Dinosaurs”.  Cycads resemble palms and grow a columnar stem which can be 3 to 50 feet tall dependent on the specie. Dissimilar to palm plants, cycads produce  xylem rings surrounding a pithy core, palms do not produce concentric ringed wood. Approximately 150 species in 10 genera of cycads exist today, mainly inhabiting tropical and subtropical regions.

Many other species of extant plants are descended from specimens found in fossil records which thrived in ancient times. For more in-depth information on living fossils of the plant kingdom, visit http://nzetc.victoria.ac.nz/tm/scholarly/tei-Bio04Tuat02-t1-body-d2.html.