Ray-fin Xiphactinus enters the LRT with the lobe-fins and Cheirolepis

Currently,
just a few traditional ray-fin fish are taxa in the large reptile tree (LRT, 1448 taxa). Even so, an interesting cladistic pattern is starting to appear.

Like other basal fish,
Xiphactinus has a long belly between the pectoral and pelvic fins (Fig. 2).

At this point the clade Actinopterygia
(ray-fin fish) is diphyletic, with the Nile bichir (Polypterus, Fig. 1) nesting basal to Crossopterygians apart from the ray-fins Cheirolepis (Fig. 1) + Xiphactinus (Figs. 2, 3; Leidy 1870; Cretaceous) together with the lobe-fin Middle Devonian Gogonasus (Fig. 1).

As mentioned earlier
some ray fins are derived from lobe fins, not the other way around or in parallel. As recovered in the LRT, traditional ray fin fish had more than one origin. I should look at a gar soon to see where it nests.

Remember,
one can only tell what a taxon is by where it nests, not by what traits are present or absent. Convergence is always lurking in cladograms, so testing a wide gamut of candidate taxa with an unbiased character list is imperative. Such a method solves all problems with high confidence. In this case it also overturns a long held paradigm. 

References
Leidy J 1870. [Remarks on ichthyodorulites and on certain fossil Mammalia]. Proceedings of the Academy of Natural Sciences, Philadelphia 22:12-13.

wiki/Sarcopterygii
wiki/Xiphactinus