I made this gumpaste bear 2 days ago and it has cracked! Can anyone tell my why? Did I put too much tylose in the fondant?

It's likely that it wasn't completely smooth to begin with and just became more noticeable as it dried.

I also use tylose, and even when I think I've put in too much I can still get it to dry crack-free by doing 2 things that never fail me...

1. I ALWAYS microwave the piece I'm working on...usually it's not more than 10 seconds since I literally warm each piece separately (leg, other leg, arm, other arm, etc.)

2. After warming, I ALWAYS firmly roll the fondant (no matter how small) into a very smooth ball...only then do I proceed with trying to shape it into something.

When I'm using templates (converse sneakers) and the fondant/tylose has to be rolled out instead of modeled, I still start from a smooth ball.