The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on an occasional schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Sunday, November 9, 2014

November 9. Sequoia





By the end of the Cretaceous, flowering plants were reaching into most of the ecological niches across the globe, and were dominant in many . But obviously, the more primitive gymnosperms such as ferns and conifers survived, as they are with us today. While some of them, such as ginkgoes, have declined in diversity, they haven’t changed much in more than 100 million years.

The genus Sequoia appears in the fossil record during the Jurassic in China, but it seems to have expanded across at least the northern continents of North America, Europe, and Asia during the Cretaceous. The species known from the Cretaceous, including Sequoia dakotensis, found in South Dakota and others found in Greenland, are extinct, and the surviving coast redwoods, Sequoia sempervirens, are the only surviving members of the genus. The giant sequoias of the Sierra Nevada are technically members of the genus Sequoiadendron, closely related but distinct from Sequoia sempervirens, the coast redwood.

Sequoias were apparently not well adapted to the polar regions, even though the climate was mild enough for plants to grow there. The closely related Metasequoia, or dawn redwood, was deciduous and lost its leaves in winter, so it had a more extended range. There may have been some hybridization between early Sequoias and Metasequoia, resulting in the modern coast redwood.

Redwoods seem to have thrived in the greenhouse conditions of the Cretaceous, but during the Cenozoic and up to the present, their range became restricted, presumably because of overall cooling that led to the glacial period of the past two million years or so. Sequoias have high water content in their tissues which makes them more susceptible to freezing than some other trees.

Sequoia cones were and are tiny compared to the massive sizes of the trees, but they are some of the most common fossils of sequoia. The name sequoia honors Sequoyah, the Cherokee who invented a system for writing the Cherokee language in the 1820s. 
—Richard I. Gibson

No comments:

Post a Comment