How did the duck-billed dinosaur tooth fossil lead scientists to believe that the plants existed in Antarctica.

Alright my friend let's put it this way if the duck billed dinosaurs were classified under herbivores and it's fossil was found in Antarctica then there would have to have been plants for them to eat.

Because hadrosaurs could not have survived without plants, their presence in Antarctica proves that plants existed there. Additionally, fossil plants have been found in Antarctica.