Question

Originally, there must have been just one type of ______________ on the Galapagos islands, but over time it diversified into many kinds, with different beak shapes. The same for tortoises. One type of ______________ must have turned into many kinds, with different shells depending on which island they lived on.

Answer 1

Answer:

bird

tortoise

Explanation:

"different beak shapes".  Beaks are often associated with birds.

"with different shells". From the phrase and the one before (The same for tortoises.), it is clear tortoises are the main topic.