The possible evolution of the anatomical relationship between fish and mammals is examined in this 2008 bestseller, Your Inner Fish by Neil Shubin . I'm curious about evolution, so it's good the author mostly uses popular language even I can understand.
Dr. Neil Shubin starts by telling of the hardships of doing paleontology in the arctic. He found a fossil fish 387 million years old and hints this may be a piece of the missing link puzzle. Recently discovered animal footprints in Poland have been dated back 395 million years—but I wasn't interested in that part of his story anyway.
The winner for me was the part comparing fish anatomy to mammals. That was absolutely fascinating and worth the wait. I can recommend Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body to any layperson interested in evolution, paleontology, or genetics. The book inspired a PBS episode in 2014: watch it on Hoopla today.