Ginkgoes, Dinos, and Seed Cones
What was the Earth like during this period?
- The Earth was relatively warm and stable during this period of time with elevated oxygen levels.
What is a cone-bearing plant?
- There are many plants that have "cones", but we are specifically referring to plants that have cones with seeds, such as a pine tree.
- Traditionally this group of plants has been known as "gymnosperms", or naked-seeded plants.
- The seeds are considered "naked", because they are not protecting inside a fruit, as seen in the flowering plants.
- There have been many cone-bearing plants that have evolved and gone extinct in Earth's history.
- This period in Earth's history had an amazing diversification of different cone-bearing plants.
- Ginkgo, conifers, and cycads are example of groups that diversified during this time period, and are still alive today.
What is a ginkgo?
Fossil ginkgophyte leaf (from Wiki Commons)
- Ginkgo biloba is the only living species of a group of gymnosperms known as the ginkgophytes.
- This living temperate representative is called the Maidenhair Tree, since the leaf is thought to look like a ladies' hair, and is common on US streets, since it is resistant to pollution and most pests.
- Ginkgo is sometimes thought to be a "living fossil" (see below).
- Ginkgophytes were a very successful group during the Jurassic Period, an age of long-necked dinosaurs.
What is a living fossil?
- An organism that is found in the fossil record and appears strikingly similar to living representatives.
- These similarities make it appear as if the organism has not changed in many millions of years.
- In reality, natural selection would still be acting on species over these years.
- There are probable genetic changes over these generations, even though the external appearance may not look like it has changed.
What is a cycad?
Male cycad, with large cone, growing in the Haupt Conservatory at The New York Botanical Garden (C) J. Boyer
- Cycads are living, palm-like plants that inhabit tropical zones.
- In fact, palm and cycads are an example of convergent evolution in the plant kingdom.
- Today, there are 11 living genera, and nearly 300 species, with a greater diversity back in the Mesozoic Era.
- Cycads have separate male and female individual, which possess enormous cones, bearing pollen or seeds, respectively.
What other plants exist during this time?
- There is a great diversity of plants that are referred to as "seed ferns" during this time period.
- They received this name, because some members look like tree ferns, with large frond-like leaves.
- Instead of producing spores, these plants had seeds.
- One of these seed fern groups gave rise to the flowering plants at the end of the period.
When did flowering plants evolve?
- To answer this question, let's go to the next section: Rise of the Flowering Plants
What was the Earth like before this time?
- To answer this question, go back to the previous section: Extinction and Seed Plants
J. Boyer, Ph.D.