1. Sillysaurus is a word very similar to the expression
silly goose. It only differs
in the sense that the said person is being so silly it's as if they were from the dinosaur era. It is used to describe someone acting very silly. In other words if someone is being funny but
ridiculous, they're being a sillysaurus.
2. Sillysaurus can also be used to refer to someone who often behaves in a very silly but funny way.