I have included a mix of primary and secondary sources for those interested in pursuing the topics in the book further. For accounts that use exploratory paleontological expeditions as a vehicle to discuss major questions in biology and geology, see Mike Novacek's Dinosaurs of the Flaming Cliffs (New York: Anchor, 1997), Andrew Knoll's Life on a Young Planet (Princeton: Princeton University Press, 2002), and John Long's Swimming in Stone (Melbourne: Freemantle Press, 2006). All balance scientific analysis with descriptions of discovery in the field.
The comparative methods that I discuss, including the methods used in our walk through the zoo, are the methods of cladistics. A superb overview is Henry Gee's In Search of Deep Time (New York: Free Press, 1999). Basically, I present a version of the three-taxon statement, the starting point for cladistic comparisons. A good treatment with background sources is found in Richard Forey et al., "The Lungfish, the Coelacanth and the Cow Revisited," in H.-P. Schultze and L. Trueb, eds., Origin of the Higher Groups of Tetrapods (Ithaca, N.Y.: Cornell University Press, 1991).
The correlation between the fossil record and our "walk through the zoo" is discussed in several papers. A sampling: Benton, M. J., and Hitchin, R. (1997) Congruence between phylogenetic and stratigraphic data in the history of life, Proceedings of the Royal Society of London, B 264:885-890; Norell, M. A., and Novacek, M. J. (1992) Congruence between superpositional and phylogenetic patterns: Comparing cladistic patterns with fossil records, Cladistics 8:319-337; Wagner, P. J., and Sidor, C. (2000) Age rank/clade rank metrics—sampling, taxonomy, and the meaning of "stratigraphic consistency," Systematic Biology 49:463-479.
The layers of the rock column and the fossils contained therein are beautifully and comprehensively discussed in Richard Fortey's Life: A Natural History of the First Four Billion Years of Life on Earth (New York: Knopf, 1998). Resources for vertebrate paleontology include R. Carroll, Vertebrate Paleontology and Evolution (San Francisco: W. H. Freeman, 1987), and M. J. Benton, Vertebrate Paleontology (London: Blackwell, 2004).
For the origin of tetrapods: Carl Zimmer reviewed the state of the art in the field in his highly readable and well-researched At the Water's Edge (New York: Free Press, 1998). Jenny Clack has written the definitive text on the whole transition, Gaining Ground (Bloomington: Indiana University Press, 2002). The bible of this transition, Clack's book will bring a novice to expert status quickly.
Our original papers describing Tiktaalik appeared in the April 6, 2006, issue of Nature. The references are: Daeschler et al. (2006) A Devonian tetrapod-like fish and the origin of the tetrapod body plan, Nature 757:757-763; Shubin et al. (2006) The pectoral fin of Tiktaalikroseae and the origin of the tetrapod limb, Nature 757:764-771. Jenny Clack and Per Ahlberg had a very readable and comprehensive commentary piece in the same issue (Nature 757:747-749).
Everything about our past is relative, even the structure of this book. I could have called this book "Our Inner Human" and written it from a fish's point of view. The structure of that book would have been strangely similar: a focus on the history humans and fish share in bodies, brains, and cells. As we've seen, all life shares a deep part of its history with other species, while another part of its history is unique.
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