Transition fossils - Part 2... Tiktaalik, the fish that could do a push up.

How did life move from water to land?

Amphibians were always considered key but there are big differences moving from fish to frogs:
-limbs
-lungs
-and often a neck

Limbs and lungs were easy enough, fossils with lobed fins with indications of developing into limbs were readily enough available, and rudimentary lungs are present in a number of fish species.

Ictheostega got us close but was decidedly amphibian, we still needed to find something decidedly fish but almost amphibian.

Enter Tiktaalik

By Eduard Solà , CC BY-SA 3.0, Link

There is a really interesting story about the prediction and hunt for Tiktaalik.

If you have an hour I highly recommend the watch, finding your inner fish by Dr. Neil Shubin, an Univeristy of Chicago Evolutionary Paleontologist who was instrumental in finding Tiktaalik:

Tiktaalik is definitely a fish but lived in shallow water, has eyes and nostrils on the top of the head (for use above the water) and it's fore-fins had all the equivalent bones we have in our forearms today. It could do a push-up and likely used these rudimentary limbs to get around on land when it was out of the water evading predators or foraging.

The case is not closed yet though, there are some other fossil trackways that buck the development trend.