Macroevolution: Drift, Extinctions, & Radiations

What is macroevolution?

Evolutionary change above the species level, including the origin of new groups and major transitions.

What are examples of macroevolutionary events?

The appearance of terrestrial vertebrates, mass extinctions, and adaptive radiations.

What theory explains Earth’s shifting continents?

The theory of plate tectonics.

What are tectonic plates?

Large sections of Earth’s crust that move over the mantle.

What drives continental drift?

Convection currents in Earth’s mantle.

How often have Earth’s landmasses formed supercontinents?

Three times over the past 1.5 billion years.

What was the most recent supercontinent?

Pangaea, about 250 million years ago.

What are the biological effects of continental drift?

Alters habitats and climates, Promotes allopatric speciation, Explains biogeographic patterns (e.g., distribution of marsupials).

What is a mass extinction?

A sudden, global increase in extinction rates that eliminates many species.

How many major mass extinctions have occurred?

Five throughout Earth’s history.

What percentage of species typically go extinct in a mass extinction?

About 50% or more.

What was the Permian extinction?

The largest mass extinction, eliminating ~96% of marine species 252 MYA.

What caused the Permian extinction?

Volcanic eruptions in Siberia → global warming, ocean acidification, and oxygen depletion.

What was the Cretaceous extinction?

Occurred 66 MYA, wiping out dinosaurs and many marine species.

What caused the Cretaceous extinction?

A meteor impact near the Yucatán Peninsula (Chicxulub crater).

What evidence supports the meteor impact hypothesis?

A layer of iridium-rich clay found worldwide.

What are the consequences of mass extinctions?

They reshape ecological communities and open new niches for surviving lineages.

What is an adaptive radiation?

A rapid diversification of species from a common ancestor to fill different ecological niches.

What often follows mass extinctions?

Adaptive radiations of surviving groups.

Give an example of an adaptive radiation.

Mammals diversified rapidly after the extinction of dinosaurs.

What is another classic example of adaptive radiation?

Darwin’s finches evolving different beak shapes to exploit distinct food sources.

How can evolutionary innovations trigger radiations?

New traits (like flight or photosynthesis) open up new ecological opportunities.

Are evolutionary trends goal-directed?

No — they result from natural selection, chance, and environmental change.

What does the fossil record reveal about evolutionary tempo?

It shows both gradual change and periods of rapid diversification.

What is heterochrony?

Evolutionary change in the timing or rate of developmental events.

What is paedomorphosis?

When adult organisms retain juvenile features of ancestors.

What role does gene regulation play in evolution?

Small genetic changes in developmental genes can produce large morphological differences.