Ammonite

Ammonites inexplicably disappeared during the late Cretaceous.

Musée du Séminaire de Sherbrooke

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Some things attract attention despite looking very ordinary. This is true for ammonites. This marine mollusc with a spiral shell has been studied in detail. Ammonites evolved very rapidly. Because we can date the different ammonite families in the Earth’s geological timeline, we can break down the history of our planet very precisely. Also, ammonites were swept by currents into all the oceans around the world, thereby linking very distant lands.

Ammonites no longer exist, but their cousin, the Nautilus, does. The Nautilus appeared 300 million years ago. It doesn’t seem any better adapted than ammonites were, just luckier!
Some things attract attention despite looking very ordinary. This is true for ammonites. This marine mollusc with a spiral shell has been studied in detail. Ammonites evolved very rapidly. Because we can date the different ammonite families in the Earth’s geological timeline, we can break down the history of our planet very precisely. Also, ammonites were swept by currents into all the oceans around the world, thereby linking very distant lands.

Ammonites no longer exist, but their cousin, the Nautilus, does. The Nautilus appeared 300 million years ago. It doesn’t seem any better adapted than ammonites were, just luckier!

© 2001, CHIN. All Rights Reserved.

Life in the seas appeared 380 billion years ago. In the Cretaceous period, many species of marine life emerged, and some organisms ceased to evolve. During this fascinating period, the seas were the battlefield of an evolutionary revolution.

Molluscs began the attack by developing tools to pierce through shells. Crabs, lobsters, crawfish and other modern crustaceans reached their full development and continued the assault. Sharks, which appeared over 400 million years ago, underwent their greatest evolution ever. Entire families of marine organisms were threatened with extinction as bony fish (teleosts) diversified and predatory reptiles emerged.
Life in the seas appeared 380 billion years ago. In the Cretaceous period, many species of marine life emerged, and some organisms ceased to evolve. During this fascinating period, the seas were the battlefield of an evolutionary revolution.

Molluscs began the attack by developing tools to pierce through shells. Crabs, lobsters, crawfish and other modern crustaceans reached their full development and continued the assault. Sharks, which appeared over 400 million years ago, underwent their greatest evolution ever. Entire families of marine organisms were threatened with extinction as bony fish (teleosts) diversified and predatory reptiles emerged.

© 2001, CHIN. All Rights Reserved.

Lobster

The lobster became fully evolved during the Cretaceous period.

Musée du Séminaire de Sherbrooke

© Musée du Séminaire de Sherbrooke. All Rights Reserved.


Bivalves

Predators took a bite out of less evolved populations. Some marine invertebrates began a sharp decline, and others burrowed ever deeper into the sediments.

Musée du Séminaire de Sherbrooke

© Musée du Séminaire de Sherbrooke. All Rights Reserved.


Some populations developed effective methods of defense. One type of bivalve, the Inoceramus, grew a shell up to two meters in size. The emergence of reefs also provided protection from predators. But it was the sea urchin that changed most remarkably at the end of this period. Most sea urchin families that appeared then still exist today. And their way of life has hardly changed.
Some populations developed effective methods of defense. One type of bivalve, the Inoceramus, grew a shell up to two meters in size. The emergence of reefs also provided protection from predators. But it was the sea urchin that changed most remarkably at the end of this period. Most sea urchin families that appeared then still exist today. And their way of life has hardly changed.

© 2001, CHIN. All Rights Reserved.

Sea Urchins

Sea urchins are covered with rigid plates that act as an external skeleton.

Musée du Séminaire de Sherbrooke

© Musée du Séminaire de Sherbrooke. All Rights Reserved.


Learning Objectives

The learner will:
  • Develop enthusiasm and continuing interest in the study of science
  • Describe some of the invertebrate marine animals of the Cretaceous and their ecology
  • Describe how evolution shaped the invertebrate communities of the Cretaceous, with examples

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