In this YouTube video from 2018
Dr. Donald Henderson starts his online slide video presentation by repeating the traditional fin-to-finger story (Fig. 1).
that story was already out-of-date in 2018 due to taxon exclusion in comparison to and competition with the phylogenetic analysis found in the large reptile tree (LRT, 1817+ taxa; subset Fig. 5).
Not surprisingly, Dr. Henderson thought it was “very peculiar”
that Middle Devonian tetrapod trackways preceded the Late Devonian fossils of tetrapods by tens of millions of years. The LRT solves this problem. Acanthostega and Ichthyostega are not transitional taxa, but dead end taxa with polydactyly not found in other tetrapod taxa. Their phylogenetic ancestors filled the gap between the Middle and Late Devonian, but those fossils have not been found yet in those strata, only in later strata as late survivors of those earlier radiations.
In the middle of the presentation
Dr. Henderson presented his alternative view: that Ichthyostega and Acanthostega were secondarily aquatic tetrapods. His YouTube video is dated January 11, 2018. Only a short month earlier the LRT recovered Ichthyostega and Acanthostega as secondarily more aquatic tetrapods, time-stamped here.
Evidently that was an idea whose time had come.
Or else Dr. Henderson read that hypothesis here and embraced it. Either way, Dr. Henderson did not employ phylogenetic analysis, but came to his solution as a notion to reconcile the Middle Devonian tracks to the late Devonian fossils.
Dr. Henderson’s presentation was mundane. Henderson’s customary family tree of vertebrates (Fig. 1) indicates he had no idea how clades of fish are related to one another at a species level (Fig. 2). He never tested traditional hypotheses, but accepted them without reservation.
The fish phylogeny problem was resolved
here in 2019 and continues to evolve with every added taxon.
Dr. Henderson also presents a traditional lineup
of tetrapods (Fig. 3) that was improved by the LRT by simply adding overlooked taxa (Fig. 4).
Henderson’s traditional lineup is lacking several taxa,
like Trypanognathus (Fig. 4), that are also long, low and with tiny limbs, like Tiktaalik and Panderichthys, but are traditionally never included in fin-to-finger cladograms, other than here in the LRT.
It’s nice to have a notion, like Dr. Henderson had.
After all, that’s where all scientific inquiry has its genesis. But you can’t beat a good old, wide gamut phylogenetic analysis to make your notion into a testable hypothesis that covers all the other competing hypotheses. Let’s hope that someday PhDs will adopt a taxon list comparable to the LRT and then let the taxa and their taxonomy tell the tale.
follow up those notions with testable analyses. It’s hard work, but it’s the professional thing to do.