Ginkgoes, Dinos, and Seed Cones

230–145 million years ago (Late TriassicEarly Cretaceous)

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?

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?

Cycads

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?

What was the Earth like before this time?

J. Boyer, Ph.D.