So far, the first three episodes of Phineas & Ferb in Primeval have been submitted. The fourth one I'm working on right now. Just to let both Primeval fans & Phineas & Ferb fans know.
Now that you mentioned it, there was a prehistoric platypus named Obdurodon that lived in Australia during the Miocene epoch. It was about the size of a modern platypus.
I don't know about that. Although if I do decide to feature Obdurodon in any future series I can also feature creatures that lived around the same time. There's the powerful thylacine, Thylacinus potens, Dromornis and Bullockornis, two large birds that are nicknamed the demon ducks of doom, or there's Quinkana, a fairly large crocodilian that hunted on land. Personally I would like to pick Quinkana.