It was during the Paleozoic Era that plants (first known from microfossils called cryptospores that appear in the mid-Ordovician, about 470 million years ago; Wellman and Gray 2000) and animals (known from Silurian fossils, at least 423 million years ago; Wilson and Anderson 2004) began to colonize the land
Nucleus; Prokaryotic Cells do not have a nucleus, whereas Eukaryotic cells do
Answer:
Migration
Explanation:
Birds have adapted to the changes in temperature (over generations) and know to migrate when necessary