Coming onto Land

Describe the 4 phases of aquatic-terrestrial adaptation (vertebrate):

1: Aquatic

2: Some terrestrial activity, adult dependent on water

3: Adaptation for weight bearing, adult dependent on water

4: Loss of gills, adult largely independent of water

Why did early terrestrial vertebrates live near water still?

Eggs with amniotic fluids hadn’t evolved yet, so they had to be laid in the water.

When did the water-land transitional period occur?

It began ~385m years ago

How long before the vertebrate invasion had land invertebrates been around?

~60m years

Describe Rhynie Chert:

• A konservat lagerstatten

• A 3D terrestrial ecosystem preserved by silica build-up from a hot spring

• E.g. micro spiders

Describe the size of invertebrates in the Carboniferous:

Huge! Could reach nearly 3m in length inc. millipedes, dragonflies, and cockroaches.

When did the first land plants appear?

In the Ordovician, 460mya.

Give some pros of moving on land (as a plant):

• Much higher solar radiation + CO2

• Symbiosis with fungi increased nutrient uptake

Give some cons of moving on land (as a plant):

• Necessitates structural support against gravity

• More variable conditions

• Need to develop seed dispersal mechanisms

Describe the first land vascular plants:

• Arrived in the Silurian e.g. Cooksonia

• Only a few mm tall

• Dense, single species stands

What are 2 keys to success as a land plant?

• Waxy cuticle to prevent desiccation

• Protection of gametes + embryos

Describe the early forests:

• Appeared in the early mid-Devonian

• 3-4m tall single species stands

• Plants didn’t have traditional trunks e.g. Cladoxylopsid, fern-like, and Archaeopteris, deep-rooted

Describe the shift in tree evolution in the mid-late Devonian:

• Root systems are bigger

• Trees get taller

• Increased Mg and Ca release (due to roots) increases reef development + eutrophication

How does the evolution of land plants correlate with atmospheric CO2?

They correlate pretty closely.