Not sure how I missed this key taxon for seven years…
Swartz 2012 described a transitional Middle Triassic marine sarcopterygian nesting between Ostelepis and Panderichthys at the base of the Tetrapoda in the large reptile tree (LRT, 1440 taxa).
Figure 1. Tinirau clacke in situ and reconstructed in lateral view from Swartz 2012, colors added. Light/dotted lines are hypothetical. Based on phylogenetic bracketing, the dorsal fins may have been lost already, as in Panderichthys. This is one of your ancestors.
FIgure 1a. Revised reconstruction of Tinirau. Compare to figure 1.
Tinirau clacke (Swartz B 2012; Middle Devonian; UCMP 118605) Distinct from earlier lobefin fish, this one has a skull twice as wide as tall, the skull bones are more tetrapod-like, dorsal ribs and a pelvis make a tentative appearance.
Figure 2. Basal tetrapods to scale. Yellow taxa are temnospondyls. Red taxa are reptilomorphs. Breaking the old paradigm, Acanthostega and Icthyostega are more aquatic than their ancestor, Ossinodus, the first taxa with big limbs and a shorter torso. Silvanerpeton is the basal reptile in the LRT. Perryella is the basal reptilomorph.
References
Swartz B 2012. A marine stem-tetrapod from the Devonian of Western North America. PLoS ONE. 7 (3): e33683. doi:10.1371/journal.pone.0033683
The Pterosaur Heresies 