So we always hear about the Roman games having lions and other animals. Is this just a guess or is there proof?
What proof or records exist to show that animals were used in the games?
There are some sources that suggest animals were used for executing criminals eg: '...those who break into a temple at night in order to pillage or plunder it are thrown to wild animals' from Paulus, Opinions 5.19-19a, which may have taken place in an area event.
It does seem however that wild animal fighters were not usually trained, and there was the expectation that they would not survive/get to leave the arena.
There are also some letters preserved between Cicero and Caelius where they complain about trying to get panthers into Rome for games that Caelius is hosting (source: Cicero, Correspondence with Family and Friends, 8.9.3, 2.11.2)
Some advertisements for amphitheatre events have also survived, which say things like 'A gladiatorial troop hired by Aulus will fight in Pompeii on May 31. There will also be a wild animal hunt' (CIL 4.1190)