Cretaceous Period: The Apex of Prehistoric Diversity

The age of dinosaurs reached its apex during the Cretaceous period, which occurred 145 to 65 million years ago. Dinosaur and other animal diversity characterized this time, as more different types of dinosaurs emerged during the Cretaceous than in any other period. Nevertheless, ominous signs began to surface, hinting at the non-avian dinosaur downfall that would mark the end of this final phase of the Mesozoic era.

Cretaceous Geology, Climate and Plant Life

Laurasia, a portion of the former Pangea supercontinent, consisted of the present-day continents of North America, Europe and much of Asia. Another section of former Pangea was referred to as Gondwana, which included Africa, Antarctica, Arabia, Australia, India and South America. Both Laurasia and Gondwana broke into pieces during the Cretaceous, leading to the separate continents. North America, however, was substantially different than it is today. A shallow sea split it in half, turning the western portion into an island.

Although wet and dry periods existed before this time, the seasons became more distinct during the Cretaceous. Flowering plants emerged, providing another food source for dinosaurs. The first flowers were mostly like small weeds but, like weeds today, they grew and spread well, quickly moving from tropical to cooler regions. Oak, maple, walnut and other trees also emerged.

The Largest Flying Animals

Cretaceous skies were full of creatures big and small. Minuscule moths and small bees shared airspace with enormous pterosaurs, which were warm-blooded flying reptiles related to dinosaurs. The pterosaur Pteranodon, which had a wingspan of up to 33 feet, was one of the biggest of the bunch. It spent much of its time soaring over water, looking for fish, crabs, insects and mollusks to eat.

Dinosaur Diversity

Big, small, spiked, fat and more, dinosaurs of all shapes and sizes appeared during the Cretaceous. Since the landmasses were now separated, animals on the distinct continents went their separate evolutionary ways. Beaked, plant-eating dinosaurs known as ceratopsians first appeared at this time. One of the most well-known members of this group was Triceratops, which had three facial horns and a large, bony frill. The so-called "bone-headed" dinosaurs also emerged during the Cretaceous. One of the biggest was Pachycephalosaurus, which had front teeth and might have even enjoyed meat with its plant-based diet.

Numerous carnivorous dinosaurs preyed upon the other dino bounty. There was Pelicanimimus, which had more teeth — around 220 — than any other known dinosaur. Afrovenator used its own bladelike teeth to tear at the flesh of prey. Carnotaurus had such short arms that its hands appeared to form out of its elbows, but its clawed feet and sharp teeth could still take down sauropods. Tyrannosaurus rex, however, stood out from the carnivorous dinosaur pack. This 40-foot-long beast was so strong that researchers believe it could shake victims to death, once it had sunk its teeth into their bodies.

Hints of Extinction

Not all dinosaurs thrived during the Cretaceous. Stegosaurs, which lacked the protective armor of other plant eaters, like ankylosaurs, went into a population decline. In northern areas, long-necked sauropods began to disappear. While minor, these changes might have foreshadowed the mass extinction that marked the end of both the Cretaceous period and the dinosaur age.