The place to make future basal tetrapod discoveries is in Late Devonian/Earliest Carboniferous strata (Fig. 1, light blue). That’s where an undiscovered radiation appears to have taken place based on the widespread dispersal of basal tetrapods in the Visean (Early Carboniferous, light green).
Sometimes what you don’t see right away
is the important story. We should see lots of Devonian tetrapods, but currently we do not.
Earlier we considered the possibility that Acanthostega and Ichthyostega were secondarily a little more aquatic, based on ancestral taxa that were a little more terrestrial. That hypothesis is based on the current cladogram (subset in Fig. 1).
Tiktaalik was discovered by searching in the desired strata. So this process does work. Maybe we’ll find more basal tetrapods in slightly higher strata.