This is an FYI. It appears that the arena battle rewards are exclusives Dinosaurs and based on a pattern.
The possible pattern for the season rewards can be found by clicking your battle button.
Next click on your arena name. Scroll to the bottom and you will see above the training grounds.
the Fallen Kingdom exclusives which are Miragaia Proceratosaurus and Alanqa
So far we have had
Proceratosaurus wake up
Next up should be
Arambourgiania… wake up December
Stygimoloch zzzzz unless second worst unique in game gets buffed enjoy your rest.
Purussaurus Wake up February
Irritator April Drink some coffee and play combat music in the background.
Stygimoloch gen 2 zzzzz unless worst unique in game gets buffed enjoy your rest.
Baryonyx gen 2 Wake up June drink coffee queue that battle music.
Gallimus zzzzz by now, you might have a level 30 gallimus and 250,000 gallimus DNA enjoy your rest.
Pachycephalosaurus Wake up August
Other exclusives or repeat.
Possibly expect to be added to the pattern
Allosaurus Gen 2