Evolution in the Ocean

Question 1

What marine organisms dominated the Cambrian seas?

Answer 1

Trilobites, sponges, brachiopods, early mollusks

Question 2

What are stromatolites and why are they important?

Answer 2

Layered bacterial mats, some of the oldest evidence of life

Question 3

What were the major reef builders in the Paleozoic?

Answer 3

Tabulate corals, rugose corals, stromatoporoids

Question 4

When did modern coral reefs (Scleractinians) emerge?

Answer 4

Triassic Period

Question 5

Which era is known as the “Age of Fishes”?

Answer 5

Devonian

Question 6

What marine vertebrates evolved in the Mesozoic?

Answer 6

Ichthyosaurs, plesiosaurs, early marine turtles

Question 7

What were the five major mass extinction events and how did they affect life in the ocean?

Answer 7

1. End-Ordovician (444 Ma) – Glaciation, marine invertebrate loss
2. Late Devonian (375 Ma) – Reef collapse, marine species decline
3. End-Permian (252 Ma) – “The Great Dying”, ~96% marine species lost
4. End-Triassic (201 Ma) – Reef decline, ammonoid loss
5. End-Cretaceous (66 Ma) – Asteroid impact, marine reptiles & ammonites extinct

Question 8

What was the Cambrian Explosion?

Answer 8

Rapid diversification of marine life around 541 Ma

Question 9

What geologic event led to widespread glaciation and marine regression?

Answer 9

Late Ordovician and Pleistocene glaciations

Question 10

How can genetic drift affect marine species?

Answer 10

• Coral bleaching can cause population bottlenecks
• Larval dispersal leading to isolated reef populations may cause founder effects
• Small or isolated populations (e.g., sea grasses, invertebrates on atolls) are more susceptible to drift