These are all obvious candidates, which of them have been done?
- Megalania/Varanus prisca, i.e. the giant komodo dragon (maybe already handled by giant lizards? 3 hex linear; ambush predator; tail whip like a dragon and realistically does quite a lot of damage; ST 30 to 40?)
- A big azhdarchid pterosaur, like Quetzalcoatlus northropicus (multi-hex jab attack, can fly but might also attack on ground, ST 20 to 25, 3-hex plus enormous wings?)
- Mylodon, the only known omnivorous ground sloth (might be in carnivore mode or herbivore mode, depending on reaction roll; ST 50 or so; not sure about speed; 4-hex; grab and crush?)