In 2004 Shubin, Daeschler and Jenkins discovered the first well-preserved Tiktaalik fossils in on Ellesmere Island in Nunavut, Canada. Tiktaalik is a non-tetrapod member of Osteichthyes (bony fish) from the late Devonian period about 375 million years before present. It is complete with scales and gills, but has a triangular, flattened head and unusual, cleaver-shaped fins. Its fins have thin ray bones for paddling like most fish, but they also have sturdy interior bones that would have allowed Tiktaalik to prop itself up in shallow water and use its limbs for support as most four-legged animals do. The fins and other mixed characteristics mark Tiktaalik as a crucial transition fossil, a link in evolution from swimming fish to four-legged vertebrates. 

Order of authorship in the original publication: Shubin, Daescher, Jenkins.

(Thanks to Juan Weiss for this reference and its interpretation.)

The authors showed that:
1) This transitional species had a set of features representing a major departure from the pattern in more primitive sarcopterygian fishes.
2) They presented data to indicate that Tiktaalik lived in a low gradient, meandering fluvial system within a subtropical to tropical climactic belt.
3) In this setting this species developed new mechanisms of head movement, respiration and body support; it could lift itself from the ground, enabling it to emerge from the water and ambulate on the ground, since it was endowed with an abundance of chest muscles.
4) The species had expanded gular plates and robust branchial elements that provided it with a mechanical basis for buccal pumping for lungs as well as gills. These elements assumed a
predominant respiratory function for air breathing.
5) Tiktaalik, unlike a fish, had a flat head, and eyes on top of its head and a neck. Thus Tiktaalik’s head architecture resembled that of the present day crocodile.

Order of authorship in the original publication: Daeschler, Shubin, Jenkins.

(Thanks to Juan Weiss for this reference and its interpretation.)