I'd suggest, on magical patroni, that a person can use an against the odds card if they want their character to have, say, a phoenix as a patronus form? (I believe Dumbledore's patronus was a phoenix) Or idk, trust that people won't give their average 16-year-old character a pegasus patronus. The earth has many interesting animals, you guys! xD

As for animagus forms, I now have a philosophical question and it is, if they can turn into extinct animals, does that mean that they can turn into animals that don't exist now, but will in 200 years because of evolution? xD Because magic doesn't follow the rules of linear time?

Idk, I'd personally say that the earth has many weird animals, why do we have to go with a dinosaur? Australia alone probably has a bunch of weird animals to pick from. You can be a special snowflake as a hummingbird bat or a thorny devil