It's difficult to say definitively which animal was the dominant animal of the Cretaceous period because "dominant" can be interpreted in different ways. It could mean:

* Most abundant: In this case, it would likely be dinosaurs, which were incredibly diverse and widespread during the Cretaceous.

* Most successful: This is a more subjective term, but you could argue that mosasaurs, large marine reptiles that dominated the oceans, were the most successful due to their evolutionary dominance in their environment.

* Largest: This would likely be Titanosaur sauropods, which were some of the largest land animals ever to exist.

Therefore, it depends on how you define "dominant"!

Here are some of the most prominent animals of the Cretaceous:

* Dinosaurs: Tyrannosaurus rex, Triceratops, Ankylosaurus, Velociraptor, and many more.

* Marine Reptiles: Mosasaurs, Plesiosaurs, Ichthyosaurs.

* Pterosaurs: Pterodactyl, Quetzalcoatlus

* Mammals: Early mammals were still relatively small and primitive.

* Birds: Birds began to diversify during this period.

Instead of focusing on one "dominant" animal, it's more accurate to say that the Cretaceous period was a time of great diversity and evolutionary success for a wide range of animal groups.