Mammals, birds, reptiles, and amphibians all have two pairs of _________________. They are all tetrapods, or _____________________________________________ animals. In the fossil record, tetrapods first appeared about ______________ million years ago (Ma). Where did they come from?
The closest relatives of tetrapods are ____________. Fish and tetrapods are both vertebrates that have a backbone with a spinal cord. Fish predate (come before) tetrapods, because their _______________ appear in rocks that are more than ________ million years old. This observation leads to the hypothesis that tetrapods evolved from ____________.
If tetrapods evolved from fish, as Darwin predicted, you would expect to find ______________________________ fossils with features of both fish and tetrapods. In Darwin’s day, such fossils had not yet been found, but today, there are many such examples.
Fill in the blanks please.