What is the name of Mario's pet dinosaur?

Mario's pet dinosaur is Yoshi.

Yoshi is a friendly dinosaur-like character who became one of Mario's most famous companions. He first appeared in Super Mario World for the Super Nintendo Entertainment System in 1990, where Mario could ride him through Dinosaur Land.

Yoshi helps Mario by eating enemies with his long tongue, swallowing certain objects, and laying eggs that can be thrown at foes. Depending on the game and color, Yoshis may also gain abilities such as flying, breathing fire, or spitting projectiles. The name also refers to an entire species, not only the familiar green individual.

Although fans commonly call Yoshi Mario's pet, Nintendo games more often present him as a friend, ally, or mount. Yoshi later became the star of the Yoshi series, beginning with Super Mario World 2: Yoshi's Island in 1995, and a playable character in Mario Kart, Mario Party, and Super Smash Bros. Bowser is Mario's enemy, while Luigi and Toad are allies rather than pets.