This is based on research presented last year at a National Geographic-sponsored TEDx conference, where scientists met to discuss which animals would be good candidates for, as they called it "de-extinction."
They chose the animals using the following criteria: Are the species desirable - do they hold an important ecological function or are they beloved by humans? Are the species practical choices - do we have access to tissue that could give us good quality DNA samples or germ cells to reproduce the species? And are they able to be reintroduced to the wild - are the habitats in which they live available and do we know why they went extinct in the first place?
But, this still leaves plenty of other animals on the table. The list of candidates is actually pretty long, considering.