SCIENCE

Researchers do not know why trees from more than 300 million years ago have more complex structures than trees today. (Independent)

How else have trees adapted?

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• Scientists are surprised at the growth pattern of ancient trees. What 300-million-year-old tree species was studied?
  • The new study examined Cladoxylopsida, extinct species of trees that may be the ancestors of modern ferns and horsetails. Learn more about cladoxylopsids here.
    • The study compares cladoxylopsid growth patterns to modern trees such as palms.
    • Cladoxylopsids thrived between the middle Devonian and early Carboniferous periods, from about 393 million years ago to 360 million years ago.

• The new research analyzed mineralized Cladoxylopsida fossils. What is the difference between mineralized fossils and petrified fossils? They’re both rocks! Take a look at this article for some help.
  • Petrification occurs when organic matter is completely replaced by minerals and the entire fossil is turned to stone. Petrification reproduces the original tissue in every detail.
  • Mineralization, also called permineralization, is the process in which the pores of organic matter are replaced by minerals. In this way, mineralization “fills in the spaces” of organic tissue to form a cast of the original. Mineralization is sometimes the first step in petrification, before structures such as plant cell walls are replaced by minerals.

• How is the growth pattern of ancient cladoxylopsids more complex than modern tree growth?
  • The Independent explains it beautifully:
    • “All trees have straw-like woody strands called xylem that conduct water from the roots to the leaves. New layers of xylem in most trees produce the familiar growth rings in trunks and branches.
      “But the new fossil discovery showed that the earliest trees had their xylem confined to the outer 5 centimeters (2 inches) of the trunk while the middle was completely hollow. [One researcher compared the dying, hollowing center to lettuce.]
      “The strands were interconnected like a finely tuned network of water pipes. And rather than the tree laying down a growth ring under its bark each year, each xylem strand generated its own growth ring. In effect, the xylem strands behaved like individual mini-trees. As the strands expanded, connections between them split apart and the diameter of the tree trunk widened.”

TEACHERS TOOLKIT

The Independent: Scientists baffled over prehistoric tree mystery

Newsweek: First Trees on Earth Ripped Themselves Apart to Grow Larger

University of California Museum of Paleontology: Introduction to the Cladoxylopsida

(extra credit!) Proceedings of the National Academy of Sciences: Unique growth strategy in the Earth’s first trees revealed in silicified fossil trunks from China