In the Cretaceous period, we could have fished in the Prairies and caught the same kinds of fish we’d catch today: cartilaginous fish, primitive bony fish and modern bony fish. These kinds of fish all appeared before the Cretaceous period.

Cartilaginous fish were the first fish to appear and the first vertebrates to develop a jaw. They included rays, chimaeras and sharks. Because of their cartilaginous skeleton, complete fossilized specimens are extremely rare. Shark teeth, however, are often discovered in sedimentary rock.
In the Cretaceous period, we could have fished in the Prairies and caught the same kinds of fish we’d catch today: cartilaginous fish, primitive bony fish and modern bony fish. These kinds of fish all appeared before the Cretaceous period.

Cartilaginous fish were the first fish to appear and the first vertebrates to develop a jaw. They included rays, chimaeras and sharks. Because of their cartilaginous skeleton, complete fossilized specimens are extremely rare. Shark teeth, however, are often discovered in sedimentary rock.

© 2001, CHIN. All Rights Reserved.

Shark Tooth

Shark Tooth

Musée du Séminaire de Sherbrooke

© Musée du Séminaire de Sherbrooke. All Rights Reserved.


Longnose Gar

The longnose gar has a heavy skeleton.

CHIN

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Modern fish appeared 220 million years ago. They underwent significant evolutionary changes in the Cretaceous period. They had a skeleton composed partly of bone, a pair of gills, and often a swim bladder that allowed them to float and dive as required. The first types of salmon and trout appeared near the end of the Cretaceous period.

The phenomenal development of bony fish (teleosts) led to the most striking changes in marine life in the Cretaceous period. Stronger skeletons and protective scales afforded bony fish certain advantages. As a result, their populations grew and quickly spread. A new source of food had just been born.

Modern fish appeared 220 million years ago. They underwent significant evolutionary changes in the Cretaceous period. They had a skeleton composed partly of bone, a pair of gills, and often a swim bladder that allowed them to float and dive as required. The first types of salmon and trout appeared near the end of the Cretaceous period.

The phenomenal development of bony fish (teleosts) led to the most striking changes in marine life in the Cretaceous period. Stronger skeletons and protective scales afforded bony fish certain advantages. As a result, their populations grew and quickly spread. A new source of food had just been born.


© 2001, CHIN. All Rights Reserved.

Brook Trout

Modern-day bony fishes, like this Brook trout, are more mobile.

Musée du Séminaire de Sherbrooke

© Musée du Séminaire de Sherbrooke. All Rights Reserved.


Reptiles, which evolved from amphibians, crawled onto land 340 million years ago. They proliferated and diversified at an astounding rate. About 250 million years ago, some land reptiles returned to the sea. These are the ancestors of marine reptiles.
Reptiles, which evolved from amphibians, crawled onto land 340 million years ago. They proliferated and diversified at an astounding rate. About 250 million years ago, some land reptiles returned to the sea. These are the ancestors of marine reptiles.

© 2001, CHIN. All Rights Reserved.

In the Cretaceous seas, the success of bony fish led to the development of predatory reptiles. One fine example of the strangeness of evolution is the Elasmosaurus, a kind of plesiosaur. This 12-metre giant had an exceptionally flexible neck twice as long as its body. The creature could move in every direction and surprise its prey by thrusting its tiny head like a harpoon. It had to be on the watch for attacks by pliosaurs (a reptile with a short neck and a massive head) and by mosasaurs (newcomers in the history of evolution). These large snake-like lizards were at the top of the food chain. Other species, such as dolphin-like ichthyosaurs and geosaurs, became extinct before the end of the Cretaceous period.
In the Cretaceous seas, the success of bony fish led to the development of predatory reptiles. One fine example of the strangeness of evolution is the Elasmosaurus, a kind of plesiosaur. This 12-metre giant had an exceptionally flexible neck twice as long as its body. The creature could move in every direction and surprise its prey by thrusting its tiny head like a harpoon. It had to be on the watch for attacks by pliosaurs (a reptile with a short neck and a massive head) and by mosasaurs (newcomers in the history of evolution). These large snake-like lizards were at the top of the food chain. Other species, such as dolphin-like ichthyosaurs and geosaurs, became extinct before the end of the Cretaceous period.

© 2001, CHIN. All Rights Reserved.

Marine Reptiles

Several marine reptiles becam extinct at the end of the Cretaceous.

Musée du Séminaire de Sherbrooke

© Musée du Séminaire de Sherbrooke. All Rights Reserved.


Turtles and crocodilians (two orders of reptiles that appeared probably over 250 million years ago) have survived to this day without undergoing major changes. The Cretaceous period saw the development of a group of turtles that could adapt to all environments and systems. This adaptation favoured their survival. Cases of gigantism weren’t uncommon. For example, the sea turtle Archelon grew over 3 metres long. As for crocodilians, they could reach a length of 15 metres. They were more abundant and widely dispersed than today.
Turtles and crocodilians (two orders of reptiles that appeared probably over 250 million years ago) have survived to this day without undergoing major changes. The Cretaceous period saw the development of a group of turtles that could adapt to all environments and systems. This adaptation favoured their survival. Cases of gigantism weren’t uncommon. For example, the sea turtle Archelon grew over 3 metres long. As for crocodilians, they could reach a length of 15 metres. They were more abundant and widely dispersed than today.

© 2001, CHIN. All Rights Reserved.

Turtle

Turtle

Musée du Séminaire de Sherbrooke

© 2008, 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 vertebrate marine animals of the Cretaceous and their ecology
  • Describe how evolution shaped the invertebrate communities of the Cretaceous, with examples

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