Sauropods dominated the southern continents but became rare in the north. Herd-dwelling ornithischians like Iguanodon spread everywhere but Antarctica. Toward the close of the Cretaceous, vast herds of horned beasts such as Triceratops munched cycads and other low-lying plants on the northern continents. The carnivore Tyrannosaurus rex dominated the late Cretaceous in the north while monstrous meat-eaters like Spinosaurus , which had a huge sail-like fin on its back, thrived in the south.
Smaller carnivores likely battled for the scraps. Other creatures, such as frogs, salamanders, turtles, crocodiles, and snakes, proliferated on the expanded coasts. Shrewlike mammals scurried about the forests. The largest pterosaur known soared overhead though the group as a whole faced ever stiffening competition from fast diversifying birds: Ancestors to modern grebes, cormorants, pelicans, and sandpipers all show up in the Cretaceous.
In the warm, shallow seas that spilled onto the continents, the long-necked plesiosaurs gave way to the giant, snakelike mosasaurs. Rays and modern sharks became common. Sea urchins and sea stars starfish thrived; coral reefs continued to grow.
Diatoms, a type of shelled plankton, made their first radiation into the ocean. But it was the rapid dispersal of flowering plants that stole the show—a spread enhanced with the help of insects from bees and wasps to ants and beetles.
Magnolia, ficus, and sassafras quickly outnumbered ferns, conifers, gingkoes, and cycads. Much of this rich life—including all dinosaurs, pterosaurs, pliosaurs, and ammonites—perished in the extinction event at the end of the period 65 million years ago. In fact, the land, seas, and skies would never be the same in the new era that dawned after the close of the Mesozoic era. All rights reserved. Tyrannosaurus Rex Tyrannosaurus rex arose during the Cretaceous period about 85 million years ago, and thrived as a top land predator until the dinosaurs went extinct 20 million years later.
Extinct Species Whether or not the asteroid or comet that carved the Chicxulub crater caused the extinction of more than half the planet's species at the end of the Cretaceous remains a matter of scientific debate.
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Animals Whales eat three times more than previously thought. While the oldest bee fossil was trapped in its amber prison only about 80 million years ago, evidence has been found that bee- or wasp-like insects built hive-like nests in what is now called the Petrified Forest in Arizona.
These nests, found by Stephen Hasiotis and his team from the University of Colorado, are at least million years old. It is now thought that competition for insect attention probably facilitated the relatively rapid success and diversification of the flowering plants. As diverse flower forms lured insects to pollinate them, insects adapted to differing ways of gathering nectar and moving pollen thus setting up the intricate co-evolutionary systems we are familiar with today.
There is limited evidence that dinosaurs ate angiosperms. Two dinosaur coprolites fossilized excrements discovered in Utah contain fragments of angiosperm wood , according to an unpublished study presented at the Society of Vertebrate Paleontology annual meeting.
This finding, as well as others, including an Early Cretaceous ankylosaur that had fossilized angiosperm fruit in its gut, suggests that some paleo-beasts ate flowering plants. Moreover, the shape of some teeth from Cretaceous animals suggests that the herbivores grazed on leaves and twigs, said Betsy Kruk, a volunteer researcher at the Field Museum of Natural History in Chicago.
During the Cretaceous Period, more ancient birds took flight, joining the pterosaurs in the air. The origin of flight is debated by many experts. Feathers probably evolved from early body coverings whose primary function, at least at first, was thermoregulation. At any rate it is clear that avians were highly successful and became widely diversified during the Cretaceous. Confuciusornis million to million years ago was a crow-size bird with a modern beak, but enormous claws at the tips of the wings.
Iberomesornis , a contemporary, only the size of a sparrow, was capable of flight and was probably an insectivore. By the end of the Jurassic, some of the large sauropods, such as Apatosaurus and Diplodocus , went extinct. But other giant sauropods, including the titanosaurs, flourished, especially toward the end of the Cretaceous, Kruk said.
Large herds of herbivorous ornithischians also thrived during the Cretaceous, such as Iguanodon a genus that includes duck-billed dinosaurs, also known as hadrosaurs , Ankylosaurus and the ceratopsians. Theropods, including Tyrannosaurus rex , continued as apex predators until the end of the Cretaceous. About 66 million years ago, nearly all large vertebrates and many tropical invertebrates became extinct in what was clearly a geological, climatic and biological event with worldwide consequences.
Geologists call it the K-Pg extinction event because it marks the boundary between the Cretaceous and Paleogene periods.
The event was formally known as the Cretaceous-Tertiary K-T event, but the International Commission on Stratigraphy, which sets standards and boundaries for the geologic time scale, now discourages the use of the term Tertiary. The "K" is from the German word for Cretaceous, Kreide. In , a geologist who was studying rock layers between the Cretaceous and Paleogene periods spotted a thin layer of grey clay separating the two eras.
Other scientists found this grey layer all over the world, and tests showed that it contained high concentrations of iridium, an element that is rare on Earth, but common in most meteorites, Kruk said in a class she co-taught on Coursera. The crater site is more than miles kilometers in diameter and chemical analysis shows that the sedimentary rock of the area was melted and mixed together by temperatures consistent with the blast impact of an asteroid about 6 miles 10 km across striking the Earth at this point.
When the asteroid collided with Earth, its impact triggered shockwaves, massive tsunamis and sent a large cloud of hot rock and dust into the atmosphere, Kruk said. As the super-heated debris fell back to Earth, they started forest fires and increased temperatures.
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