Dinosaurs

Dinosaurs are ancient reptiles that are extinct in the real world. Dinosaurs and the related pterosaurs, have appeared in the various continuities of the Sonic the Hedgehog series in some form at least once.

Games
Dinosaurs appear in abundance in Dinosaur Jungle, the second World of Sonic and the Secret Rings. The dinosaur species featured include Triceratops, Parasaurolophus, Tyrannosaurus rex, Pteranodon, Stegosaurus, Apatosaurus and Allosaurus.

Additionally, one of the many decorations Sonic and Blaze can get for Southern Island in Sonic Rush Adventure is an Apatosaurus. While not technically a dinosaur, one of the bosses of the said game, Ghost Rex, is a mechanical dinosaur.

Archie Comics
Dinosaur-like creatures known as Mobosaurs were the first Mobian species to evolve after the Xorda's destructive attack on the planet. The Mobosaurs were wiped out during the Coming of the Chaos Emeralds, with only three surviving: the Ancient Walkers.

Adventures of Sonic the Hedgehog
Three famous dinosaur species called: Brontosaurus, T-Rex and Pterodactyl appeared in the Adventures of Sonic the Hedgehog episode "Prehistoric Sonic" there only two of them where roboticized by Robotnik's Robot-Transmogrifier Ray.

Sonic the Hedgehog (TV series)
A race of quadrupedal dinosaur-like creatures known as Terapods appear in the Sonic the Hedgehog television series episode "Sonic Past Cool".

Sonic the Comic
Sonic the Comic features the largest appearance of dinosaurs in the Sonic series so far.

The most often seen dinosaur species were the Kohenyu, who were unintentionally hunted to extinction by the Ancient Echidnas. The remains of the Kohenyu reside in the Kohenyu Graveyard, where the Spirit of the Herd is kept "alive" by the Soul Crystal.

In the present day, the inhabitants of the Great Mobian Prairie raised a herd of pterodactyls.

The lizard Society Max, partner of Mighty's father Blockhead Bill, can turn into a giant red dinosaur by eating a Mandrake Root.

Doctor Robotnik also modeled the designs of the Badniks Mekanik and Rexon after the dinosaurs.

During a series of time-and-dimensional travels with the Ring of Eternity, Amy Rose and Tekno the Canary discovered that life on several worlds, Mobius included, was created by a race of dinosaurs in spacesuits.