Well-Evolved Sloth should be able to solo Giganotosaurus, I guess.
Birdies could not kick Giga: You need to attack multiple times, and also you'll get shattered by Group Attack and Cleanse (though that's after-hand ability, RNG still sucks)


Tips:
1x Balanced Hitter + 1x Heavy Hitter + 1x Counter Attacker
*** Giga with All T5 Boosts, besides, FDC is able to remove 2 turns Debuff like Distraction and DoT
** Deinotherium with Ferocious Impact, can make 2871 damage as one attack
** Megalosaurus, with Distraction Immunity you cannot land that Debuff for emergency defense. Before getting Countered, try to do something else instead of attacking

Recommend:
Giganotosaurus - C-Class (1T), Heavy Attacks
Megalosaurus - Heavy Attack (DS), DoT (?)
Deinotherium - Slow Resist / Heavy Attack (DS), DoT (?)
...
https://www.youtube.com/watch?v=rH25StztCmk