Other Life in the Cretaceous
Besides dinosaurs, what other animals were present during the Cretaceous period?
Similar to the Jurassic, there were many other animals that surrounded the dinosaurs, competing for space and food. Most of them are familiar from the Triassic and Jurassic periods; while others diversified and evolved. But not all creatures survived; many became extinct, probably because competition increased.
Frogs, salamanders, newts, toads and caecilians, all modern amphibians: They continue to evolve and diversify.
Turtles: Archelon, a large sea turtle, grows up to 12 feet (4 meters) in length. Snakes: Earliest known snakes appear.
Crocodiles: Many crocodiles become massive, including the Deinosuchus, a large terrestrial crocodile that reached 50 feet (15 meters) in length.
Lizards: True lizards continue to evolve and diversify.
Triconodonts: Late Triassic to Late Cretaceous mammals; one of the oldest fossil mammals; three cusps of teeth in a straight row give them their name.
Symmetrodonts: Late Jurassic to Early Cretaceous mammals; they had upper and lower cheek teeth with many cusps in a triangular pattern.
Multituberculates: Late Jurassic to Late Eocene mammals; they had cheek teeth with many cusps in more than one row; they probably filled a “rodent” niche that had once been filled by cynodont therasids, and was later filled by true rodents.
Monotremes: First appearance, Early Cretaceous to the present; these animals eventually led to the true mammals (especially with hair and mammary glands). Today, there are three species of monotremes, which are mammals that lay eggs: the Australian duck-billed platypus and two kinds of echidnas (spiny anteaters), which live in New Zealand and Australia.
Early marsupials: First appear during the Middle Cretaceous and survive to the present; these pouched animals had distinct lower and upper cheek teeth.
Early placentals: Middle Cretaceous to the present; the mother nourished her developing fetus through a placenta; the cheek teeth were even more elaborate; the Late Cretaceous placental mammals include insectivores, or mammals that ate insects.