Paleontologists did not just stumble across Tiktaalik. Instead, they formed a hypothesis about where they would find a transitional form between fish and tetrapods. What might have been the logical first step in deciding where to look for a transitional form between fish and tetrapods?

Tiktaalik is the extinct sarcopterygian that lived around 375 million years ago. This is commonly known as lobe-finned fish. This fish is considered as the connecting link between tetrapods and fish.

The scientists needs proper evidence to declare the fish as the connecting link. They should study the fossils  and study the different sedimentary rocks. the rocks must be formed around 380 million years ago.  The specific chemical is used and compared its half life to confirm the study.

the answer is:

carbon dioxide

i believe the answer is snake.