Tiktaalik roseae, nicknamed the fishapod (short for fish tetrapod) lived approximately 375 million years ago. Tiktaalik roseae is a sarcopterygiian fish (lobe-finned fish, the same class as coelacanths!). The fishapod was discovered in 2006, since then, research has shown that this fossil provides a "missing link" in the evolution of tetrapods--the fishapod fits neatly in the fossil record between fish and terrestrial vertebrates.
What makes the fishapod distinct is its flat head and neck that is more characteristic of tetrapods. Its cranial features suggest that the cranial features associated with land animals first evolved from animals that lived in shallow water environments.
The fishapod has a more flexible neck than fishes--its hyomandibula, a bone that is near the mandible, is smaller than the hymandibula of true fishes. The smaller hyomandibula could indicate that the fishapod relied less on gill respiration than true fishes. The paper discusses in depth the implications that the morphology of the braincase, gill arches and palate have in relation to the evolution of tetrapods. I'd be curious to know about any genetic work done since this paper....
|Artistic reconstruction of a fishapod|
Jason P. Downs, Edward B. Daeschler, Farish A. Jenkins, Neil H. Shubin (2008). The cranial endoskeleton of Tiktaalik roseae Nature, 455 (7215), 925-929 DOI: 10.1038/nature07189.
The fishapod has its own fun, interactive website!
3D scans of the pelvis and skull: http://tiktaalik.uchicago.edu/3DTik.html