Fossil plants: Araucaria cones, Lepidodendron bark and Carbonoferous ferns.
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Most of modern-day conifers like pine, fir, or spruce have needles to perform photosynthesis. However, Araucaria, the tree that produced this cone, had scale-like leaves. Approximately 160 million years ago, a Jurassic forest of large Araucaria trees was suddenly covered by volcanic ash. The volcano erupted at the time when the cones were reaching maturity. What you see is an Araucaria cone cut in half. The elongated structures of milky color on the surface of the cross section represent seeds. It should be noted that Araucaria forests still exist in Northern parts of Argentina and even in Patagonia, for instance, Conguillio National Park in Chile. Due to their abundance during the Jurassic period, Araucaria trees likely represented a staple food of plant-eating dinosaurs like long-necked sauropods, mostly quite large creatures that constantly munched young leaves, filling their bellies with enormous amount of low-calorie food. I wonder if the seeds were also included into the diet of other animals that took advantage of this resource.
The scientific name of the Araucaria trees that produced these well-preserved fossilized cones is Araucaria mirabilis. Mirabilis means “wonderful” or “marvelous” in Latin. By the way, the word Araucaria is derived from “Araucanos”, which refers to the Native people of Patagonia, also known as Moluche or more recently Mapuche.
Let's move from the Jurassic forest to the swamps of Carboniferous period. Approximately 300 million years ago, the territory of modern-day central United States had a warm and moist climate where primitive plants thrived in massive quantities. Here is an example of typical Carboniferous plants - ferns. I fact, it has imprints of 2 different types of ferns. This rock came from a coal mine in Alabama and is a curious byproduct of a once thriving industry. Back then, during Carboniferous times, plants grew fast, producing tons of organic matter that eventually become a source of coal deposits. The coal itself is almost pure carbon with no signs of plants left. However, the plants that got mixed with fine, sediment-like mud left plenty of imprints allowing the reconstruction of ancient ecosystem. It consisted of large tree-like plants called Lepidodendrons. When the scaly leaves of Lepidodendrons fell off, they left scars on the trunk, and this is what we see on this fossil. Each species had rather distinct pattern of the scars. This particular one is likely belongs to Lepidodendron aculeatum. The fronds, leaves and scales of Carboniferous plants relentlessly transformed sunlight into the energy of chemical bonds of organic molecules like sugars to be used in biochemical reactions. By doing that, plants were capturing carbon dioxide from and adding oxygen to the air. An enormous amount of carbon was accumulated as organic matter, which became coal. Humans appeared much later and found the way to dig out coal and utilize the energy of an ancient sun to fuel industrial revolution and power up production machines, steam trains and steam boats. Sadly, it also resulted in pumping back tons of CO2 into Earth atmosphere. Most Lepidodendrons had only straight stalks. The branching started at the end of the life cycle when plants reached maturity and were about to produce spores. By the way, plants that reproduce only once in their lifetime are called monocarpic.
Finally, a few words about false trunks of tree ferns. They have a complex anatomy but it can be simplified by saying that they consist of a bundle of roots and leaf petioles mixed together to support each other like threads in a rope. The roots are round and smaller in cross-section compared to petioles. Such a structure was not only strong and flexible but also allowed to absorb the moisture all the way along the false trunk. The closer to the top of the plants, the more frequent the petioles are, and the less frequent the roots are. Thanks for watching, liking and sharing our videos! Time to say goodbye.
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