Tiktaalik is not merely here for your viewing pleasure, it is a transitional fossil. It meets every plausible criteria for being a transitionary stage between fish and tetrapods by being in the right sequence between these two forms, being in the right aged strata, and showing characteristics of both groups in a number of features.
“Tiktaalik is a transitional fossil; it is to tetrapods what Archaeopteryx is to birds. While it may be that neither is ancestor to any living animal, they serve as proof that intermediates between very different types of vertebrates did once exist. The mixture of both fish and tetrapod characteristics found in Tiktaalik include these traits:
* Fish
o fish gills
o fish scales
* “Fishapod”
o half-fish, half-tetrapod limb bones and joints, including a functional wrist joint and radiating, fish-like fins instead of toes
o half-fish, half-tetrapod ear region
* Tetrapod
o tetrapod rib bones
o tetrapod mobile neck
o tetrapod lungs
“Tiktaalik generally had the characteristics of a lobe-finned fish, but with front fins featuring arm-like skeletal structures more akin to a crocodile, including a shoulder, elbow, and wrist. The rear fins and tail have not yet been found. It had rows[6] of sharp teeth of a predator fish, and its neck was able to move independently of its body, which is not possible in other fish. The animal also had a flat skull resembling a crocodile’s; eyes on top of its head, suggesting it spent a lot of time looking up; a neck and ribs similar to those of tetrapods, with the latter being used to support its body and aid in breathing via lungs; well developed jaws suitable for catching prey; and a small gill slit called a spiracle that, in more derived animals, became an ear.”
Not only do we find Tiktaalik with features of both fish and tetrapods, but we find Tiktaalik in a sequence of progressively more tetrapod-like creatures exactly where the theory of evolution predicts he should be. Let’s take a little trip through time paying especial attention to the sequence these fossils are found in. Starting at Tiktaalik and working backwards into time we should start finding similar “fishapods” with more and more fish-like traits which is precisely what we see with Panderichthys, then Eusthenopteron, and then Osteolepis. Now, let’s jump back to Tiktaalik and move forward in time looking for its descendants with less and less fish traits and more and more tetrapod traits which brings us to Elginerpeton, then Acanthostega, and Ichthyostega. It’s also relevant to note not only the sequence in which these transitional forms occur but also their environments which shows a progression from the sea to shallow swamps to land that looks like this, as well as the fossil evidence for the adaptation of limps from fins corresponding to this evolutionary timeline found here and here and the fossil evidence for the adaptation of skull forms corresponding to this evolutionary time line found here.
So, to recap, not only does Tiktaalik meet the criteria as “transitional” by sharing numerous features of both fish and tetrapods, but he is part of a lineage of creatures that appears in an evolutionary sequence. If you have another theory that explains not only why Tiktaalik shares these common traits but also why he appears in the fossil record in sequence of both time and environment I would love to hear it.
Itinerant Lurker 