Here is the full list of all 23 Gigantosaurus: Dino Kart achievements.
Complete the Savannah Cup in Adventure
Come across Giganto
Find a shortcut
Win the first race in single player
Win The first race in adventure
Drift for 30 seconds in a race
Drift for 5 seconds in a row
Use a Skill for the first time
Win 10 Races
Unlock all characters
Unlock all tracks
Unlock all vehicle’s skins
Win a race in split-screen
Win a 4 player split-screen race
Step on a boost pad 30 time
Accumulate 10 minutes of total drift
Fly for 5 minutes totally
Finish The Tutorial
Use all skills
Win all the adventure races in third position or better
Win all the adventure races in first position
Complete the Jungle Cup in Adventure
Complete the Mount Oblivion Cup in Adventure