EvolutionLesson 2 of 3 in the course Macroevolution and mass extinctions

Cambrian Diversification: Fossil Evidence, Dating, and Proposed Causes

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

The Cambrian explosion, also called the Cambrian radiation or diversification, was an interval of rapid evolutionary diversification beginning about 538.8 million years ago, near the start of the Cambrian Period. It lasted roughly 13 to 25 million years. During this interval, many animal groups diversified, and the fossil record shows the first appearances of representatives of nearly all major animal phyla.

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Phylum
A high-level animal classification based on broad features of body plan and development.
Crown group
A group containing living members and their last common ancestor and descendants.
Stem group
Extinct relatives branching off before a crown group’s last common ancestor.
Radiometric dating
Estimating rock ages by measuring radioactive elements and their decay products.
Convergent evolution
The independent evolution of similar features in different groups.

Quiz questions

  1. About how long did the Cambrian explosion last?Answer: Roughly 13 to 25 million years.
  2. How does cladistics infer evolutionary relationships among organisms?Answer: By comparing characteristics to infer groups that share common ancestors.
  3. What makes lagerstätten especially informative about Cambrian animals?Answer: They can preserve abundant fossils and details of soft tissues.
  4. What do molecular clocks use to estimate when lineages diverged?Answer: The accumulation of genetic changes over time.
  5. What is one proposed role of rising oxygen levels in Cambrian diversification?Answer: They may have supported larger bodies and energy-demanding activities.

Based on the Wikipedia article Cambrian explosion, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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