Biota - Lifeforms

Dinosaurs were the dominant land animals, especially duck-billed dinosaurs like Shantongosaurus and horned dinosaurs like Triceratops. Giant marine reptiles such as ichthyosaurs, mosasaurs and plesiosaurs lived in the oceans, and flying reptiles lived in the skies. Flowering plants appeared in the early Cretaceous and became more common as the Cretaceous progressed.

Although larger dinosaurs such as the carnivorous Tyrannosaurus and the herbivorous Iguanodon are well known, the Cretaceous period was also home to many smaller dinosaurs. During the Cretaceous, the large three-horned dinosaur Triceratops lived in western North America. Titanosaurus, which appeared in the late Cretaceous, was the largest land animal ever recorded, along with Argentinosaurus, Dreadnoughtus and other theropods.

The Triassic and Jurassic periods witnessed the evolution of several species of small mammals that are now extinct, but two important groups of modern mammals evolved during the Cretaceous. Embryonic mammals, including most of today's mammals, evolved during the Late Cretaceous. Cretaceous embryonic mammals were ready to dominate the terrestrial environment as soon as the dinosaurs disappeared. Another group of mammals, marsupials, also evolved during the Cretaceous. These include Australian species such as the kangaroo and koala, and the North American opossum.

In the sky, flying reptiles called pterosaurs dominated. Birds evolved from their reptilian ancestors during the Jurassic and Cretaceous periods. Hesperornis was a Cretaceous genus of flightless diving birds with large feet and sharp rear-facing teeth suitable for fishing.