What is the flat head on the fish fossil most likely a sign of?

Jenkins Jr, was published in the April 6, 2006, issue of Nature and quickly recognized as a transitional form. Shubin from the University of Chicago, and Harvard University Professor Farish A. Daeschler of the Academy of Natural Sciences, Neil H. The first well-preserved Tiktaalik fossils were found in 2004 on Ellesmere Island in Nunavut, Canada. This and similar animals might be the common ancestors of all vertebrate terrestrial fauna: amphibians, reptiles, birds, and mammals. Those fins and other mixed characteristics mark Tiktaalik as a crucial transition fossil, a link in evolution from swimming fish to four-legged vertebrates. 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. Unearthed in Arctic Canada, Tiktaalik is a non-tetrapod member of Osteichthyes (bony fish), complete with scales and gills – but it has a triangular, flattened head and unusual, cleaver-shaped fins. Tiktaalik is estimated to have had a total length of 1.25–2.75 metres (4.1–9.0 ft) based on various specimens. Tiktaalik ( / t ɪ k ˈ t ɑː l ɪ k/ Inuktitut ᑎᒃᑖᓕᒃ ) is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the Late Devonian Period, about 375 Mya (million years ago), having many features akin to those of tetrapods (four-legged animals).

What is the flat head on the fish fossil most likely a sign of?