Tungsenia, the earliest stem tetrapod?

This appears to be another case of
taxon exclusion.

Lu et al. 2012
considered Tungsenia paradoxa (Early Devonian; Fig. 1) the earliest known stem-tetrapod (= taxa closer to tetrapods than to lungfish; Fig. 2).

By contrast
in the large reptile tree (LRT, 1630+ taxa; not yet updated) Tungsenia nests with similar and coeval stem-lungfish like Youngolepis (1981), Kennicthys (1993) and Guiyu (2009, Fig. 3), which was published three years earlier and found in Late Silurian strata. So Tungsenia is not the oldest member of this clade either.

Lu et al. considered Guiyu
a basal osteichichthyan (not related to stem-lungfish + stem tetrapods) and together with Psarolepis, made these outgroup taxa in their analysis. The stem tetrapods, Cabbonichthys (1997) and Tinirau (2012) are not mentioned in the Lu et al. text, the latter due to a later publication date.

Figure 1. Skull of Tungsenia from Lu et al. 2012. Tetrapod skull colors added and restored based on related taxa. Here the tooth-bearing portion of the premaxilla is missing. So are the vomers, which may have had fangs, like those of Youngolepis (Fig. 4),

Figure 2. Skull of Tungsenia from Lu et al. 2012. Tetrapod skull colors added and restored based on related taxa. Here the tooth-bearing portion of the premaxilla is missing. So are the vomers, which may have had fangs, like those of Youngolepis (Fig. 4),

Lu et al. were working from a traditional paradigm
that nested rhizodontids, like Barameda, with stem tetrapods. The LRT nests rhizodontids at a more basal node than stem lungfish + stem tetrapods due to the addition of several more basal chordate and basal vertebrate taxa that resolve the basal dichotomy between many ray fin fish and the rest of the ray fin fish + lobe fin fish.

Figure 2. Cladogram from Lu et al. 2012. Overlay approximates the new topology based on the LRT.

Figure 2. Cladogram from Lu et al. 2012. Overlay approximates the new topology based on the LRT. Frame changes every 5 seconds.

In the LRT
the cladogram of basal vertebrates (= fish) differs from traditional cladograms due to the addition of taxa not traditionally tested together. That means if workers expand their taxon list to more or less match the LRT they, too, should recover a similar tree topology. If anyone tries this, let me know your progress, issues, etc.

Lu et al. report,
“Tungsenia resembles Kenichthys, and basal dipnomorphs (for example, Youngolepis and Powichthys) in the medioventrally directed snout, the infraorbital sensory canal running along the suture between the premaxillary and neighbouring bones, the broad orbital tectum and the well-developed basipterygoid processes.” 

Adding taxa
brings more taxa, including Tungsenia, into the stem-lungfish clade.

Figure 1. Feeding strategies for basal vertebrates (fish).

Figure 3. Feeding strategies for basal vertebrates (fish). Stem tetrapods are not shown here, but nest at the lower left. Tungsenia is not listed here, but nests with Youngolepis.

Figure 3. Youngolepis skull. Colors added.

Figure 3. Youngolepis skull. Colors added.


References
Lu J, Zhu M, Long JA, Zhao W, Senden TJ, Jia L and Qiao T 2012. The earliest known stem-tetrapod from the Lower Devonian of China. Nature Communications. 3: 1160. doi:10.1038/ncomms2170

wiki/Tungsenia

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