Lesson 16

16

The Era of Fishes: The Devonian

How did life make the leap from water to land?

The Devonian Period brought a wide variety of fishes, early forests, and changes that helped some vertebrates move into shallow water and onto land. Fossils such as Tiktaalik provide evidence of the transition from fins to limbs.

Click here to hear the lesson video

Key Ideas

• The Devonian is called the 'Age of Fishes': fish diversified into hundreds of forms, including the first sharks.
• Plants grew tall for the first time, creating Earth's first forests.
• Some fish began developing sturdy, limb-like fins to crawl in shallow water: the tetrapod transition.
• Tiktaalik is a famous 'fishapod' fossil showing the transition between fish and four-limbed land animals.
• The first forests absorbed huge amounts of CO2, changing the atmosphere and climate.

Spines

• DK's Science as You've Never Seen it Before:
• Mammoth Science: Plants pg. 42, Seeds pg. 46
• Visual Timelines: Life on Earth pg. 32-39
• Alternative: Kiddle: Devonian
• Alternative: Kiddle: Evolution of Fish

Vocabulary

• Devonian: A period (~419–359 million years ago) known as the 'Age of Fishes' and marked by the first forests.
• Tetrapod: A four-limbed vertebrate; the first tetrapods evolved from lobe-finned fish and were ancestors of all land vertebrates.
• Lobe-Finned Fish: Fish with strong, fleshy fins supported by bones similar to limb bones; ancestors of the first land animals.
• Tiktaalik: A fossil 'fishapod,' a transitional species between fish and four-limbed land animals, about 375 million years old.
• Amphibian: A vertebrate that can live both in water and on land; the first amphibians evolved from lobe-finned fish.
• Vascular Plant: A plant with internal tubes that transport water and nutrients; their evolution allowed the first forests.

Discussion Questions

1. What changed on the land during the Devonian?
   Sample Answer: It went from being rocky and bare to being covered in green plants and the first big trees.
2. What did some fish start doing with their fins?
   Sample Answer: They used them like little legs to crawl through shallow water and mud.
3. Why is the Devonian called the 'Age of Fishes'?
   Sample Answer: Fish went through a huge explosion of diversity, including the rise of sharks and the lobe-finned fish that led to land animals.
4. How did the evolution of tall trees affect Earth's atmosphere?
   Sample Answer: The first forests absorbed huge amounts of CO2, which changed the atmosphere and the climate.

Digging Deeper

1. What makes Tiktaalik such an important fossil?
   Sample Answer: It is a transitional fossil that shows the change between fish and four-limbed land animals. Scientists predicted they would find it in Arctic Canada based on the age and type of rock, and they found it in 2004.