The Evidence for Evolution - How Science Works: Evolution - page 71

Fig. 4.19
The older fossils at the bottom show gill covers, fins and fish tails but no neck,
while at the top, the gill covers have gone, the fins are now limbs with digits, there
is a neck, but the fish tail is still present. In the middle is a fossil called Tiktaalik, an
Inuit name reflecting that it was found recently in the Canadian Arctic. This find was
reported in the journal Nature in 2006. Tiktaalik has fish scales, but no gill covers
and the pectoral fins are almost, but not quite, tetrapod limbs - they still have fin
rays. These fins would have allowed paddling, but they also have substantial bones
that would have enabled Tiktallik to prop itself up in shallow water but not to walk.
A remarkable feature of the discovery of Tiktaalik is that it was not entirely
accidental - the fossil hunters who found it were looking for it! By comparing
the known fossils shown in Fig. 4.19 that link fish with tetrapods, they formed the
hypothesis that the invasion of the land by vertebrate animals took place in a river
environment some 375 million years ago. So they looked for fossils in rocks of this
age whose geology suggested they had formed in a river delta. Looking for fossils
requires unusual amounts of patience and it took five expeditions to Canada before
they were successful. This remarkable story is related by Neil Shubin, one of these
fossil hunters, in his topic Your Inner Fish (see Further Reading). This is a good
example of science in action - you identify a problem with existing knowledge,
form a hypothesis about a possible solution and then seek observations or perform
experiments to test that hypothesis.