What Caused the Ammonites’ Extinction?

This article is an excerpt from the Shortform book guide to "The Sixth Extinction" by Elizabeth Kolbert. Shortform has the world's best summaries and analyses of books you should be reading.

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What are ammonites? When did they become extinct? What are the suggested causes behind ammonites’ extinction?

Ammonites are a group of coil-shelled mollusk animals that went extinct 66 million years ago. Scientists don’t know the exact cause of ammonites’ extinction, but it is theorized that they died as a result of ocean changes due to the asteroid strike.

Keep reading to learn about ammonites’ extinction causes.

The Extinction of Ammonites

Scientists don’t know what specific effect—for instance, whether heat, cold or a change in ocean chemistry—caused ammonites’ extinction but not their cousins’, the nautiluses. 

Ammonites lived in the world’s oceans for more than 300 million years—their fossilized shells have been found worldwide. They built spiral shells with multiple chambers that ranged from palm-size to wagon-wheel size. 

No one is sure what the soft-bodied animals looked like because only their shells were fossilized, but they may have looked something like octopuses.

It’s theorized that ammonites may have died from ocean changes due to the asteroid strike, because their hatchlings floated near the surface of the water. In contrast, nautilus hatchlings may have survived because they hatch in deep water and stay there as they develop for at least a year.

Everything that’s alive today descended from an organism that survived the asteroid’s impact. But it was luck, including distance from impact, heat, tsunamis, and so on—not adaptation—that allowed some species to survive. 

In a sudden mass extinction, there’s no time to adapt and pass on survival traits to offspring. Also, traits that have been beneficial for millions of years—like floating near the surface of the ocean as ammonites did—can suddenly become deadly.

What Caused the Ammonites’ Extinction?

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  • How humans have set in motion a sixth mass extinction
  • The 5 mass extinction events that occurred over the last 500 million years
  • Why human ingenuity might be able to save the human species from extinction

Darya Sinusoid

Darya’s love for reading started with fantasy novels (The LOTR trilogy is still her all-time-favorite). Growing up, however, she found herself transitioning to non-fiction, psychological, and self-help books. She has a degree in Psychology and a deep passion for the subject. She likes reading research-informed books that distill the workings of the human brain/mind/consciousness and thinking of ways to apply the insights to her own life. Some of her favorites include Thinking, Fast and Slow, How We Decide, and The Wisdom of the Enneagram.

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