Translation:Fortunately we reached the Serengeti and saw animals
The ka- tense is not one I'm really familiar with in practice. But I believe it could work as it would be "then saw." However infinitives like 'kuona' can be translated in a few different ways rather than just 'to see' for example it can also be a gerund 'seeing.' Obviously there is no way to make an infinitive past tense. So I just assumed to leave it as 'kuona'. I don't have a very technical explanation other than that through practice I just knew the infinitive is acceptable. Sorry if that is no help!