Dinosaurs are a type of species that live in the Lost Cities. The elves make sure that no species go extinct, and dinosaurs are not an exception. In Book 1: Keeper of the Lost Cities, it's shown that dinosaurs are still alive, unlike what humans believe. The elves prevented them from going extinct by keeping them in animal preserves, in order to hide them from humans. Contrary to human's ridiculous imagination of scaly monsters, dinosaurs actually are covered in bright, colorful feathers.
The Lambeosaurus was not encountered by Sophie in the lost cities but was in the museum where Fitz found her. Sophie recited the museum's information about this species after Mr. Sweeney accused her of not paying attention.
The Albertosaurus is a dinosaur covered in deep violet feathers. Sophie first met Fitz under a green, scaly model of one, and he commented that it seemed absurd that they would have looked like that. She also gave him a toy of one for midterms, thanking him for showing her what dinosaurs really looked like.
Stegosauruses were briefly mentioned when Elwin commented on Sophie holding Ella during her first appointment. He stated that he has a stuffed stegosaurus named Stinky that he can't sleep without. Also, it was later mentioned that a stegosaurus at Havenfield was stung by a manticore.
Also known as T-rex, there is a Tyrannosaurus Rex living at Havenfield named Verdi. Verdi has huge yellow eyes, sharp claws, and a pointed snout, as well as sharp fangs and neon green feathers. Verdi is also described as being "twice the size of an elephant." (Details on Verdi are in Book 1: Keeper of the Lost Cities, page 202, e-book version)
Eckodons are amphibious dinosaurs mentioned in Book 4: Neverseen. Six of them help to transport Sophie and her friends to Alluveterre for the first time. They have slightly pointed noses, long necks, and gills lining their cheeks.
Fintan is shown to be saving a family of these dinosaurs from a firestorm from a volcano in one of his memories from when Sophie was in his mind.
Pannoniasauruses are bluish-gray creatures, that look like the massive offspring of an alligator, eel, and a shark. It was mentioned that these creatures have beady eyes, and long snouts, that have a huge quantity (possibly millions) of malicious teeth. They’re a rare type of mosasaur, that thrives in freshwater. Like dolphins, when these animals are in a group, they are called a pod. Lady Cadence stated that she is very close to a specific pod of five Pannoniasaurus. After this statement, one of these mosasaurs jumped out of the water, whipping its massive tail at Lady Cadence, although she was claiming that they were just trying to get her to swim with her, stating, "that's how we usually spend our mornings." Riverdrift is moved upstream by these creatures.
There is also an undisclosed number of dinosaurs living in the mountain reserve.