Schoch 2018 tries to figure out Dissorophoids

Schoch 2018
recovered a cladogram he considered ‘dissorophoid temnospondyls’, and considered them putative lissamphibian precursors. This study closely follows a similar one by Pérez-Ben, Schoch and Báez 2018 that we looked at earlier here.

Schoch 2013 defined Dissorophoidea
as “The least inclusive clade containing Micromelerpeton credneri and Dissorophus multicinctus” (Fig. 2). In the the large reptile tree (LRT, 1837+ taxa, subset Fig. 1, non-ghosted taxa) that clade also includes Microsauria, Seymouriamorpha, Reptilomorpha and Reptilia, which was not Schoch’s intention. And it excludes several taxa Schoch included. This was all due to taxon exclusion and following tradition.

Laurin 1998 defined Temnospondyli
to include “all choanates more closely related to Eryops than to amniotes.” This is a poor definition because it doesn’t have a last common ancestor. Moreover, in the LRT no relatives of Eryops are related to Dissorophus (Fig. 2) and the dissorophoids (Fig. 1).

Figure 1. Subset of the LRT focusing on basal tetrapods (ghosted). Cherry-picked taxa from Schoch 2018 are shown in green. The least inclusive clade is not ghosted. Much better to let your cladogram tell you which taxa are putative lissamphibian stem-group taxa, than to gerrymander your own taxon list.

Unfortunately
taxa exclusion mars the Schoch 2018 study. He did not see the microsaur and reptile connection to this clade (Fig. 1). It is much better and more scientific to let your cladogram tell you which taxa are putative lissamphibian stem-group taxa, than for you to tell your claogram what the taxon list will be.

Figure 2. Dissorophus nests with Stegops among basal lepospondyls in the LRT.
Figure 2. Dissorophus nests at the base of the Dissorophidae in the LRT. And that clade is basal to Seymouria, Reptilomorpha, Microsauria, Reptilia and Lissamphibia.

Shoch 2018 reported,
“This study aims to resolve or constrain the following major questions of dissorophoid phylogeny:

  1. What does the large-scale phylogeny of Dissorophoidea look like?
  2. What is the position of the enigmatic taxon Perryella?
  3. Do Micromelerpetidae form a clade and where do they nest?
  4. Do Branchiosauridae form a clade and where do they nest?
  5. What is the relationship of Doleserpeton and Gerobatrachus to Lissamphibia/Batrachia?
  6. What is the most likely evolutionary scenario for the origin of the Dissorophoidea
  7. and the origin and early diversification of Lissamphibia/Batrachia?
  8. The goal of the phylogenetic analysis was to cover as wide a range of well-studied dissorophoid taxa as possible, with the focus on the origin and diversification of this clade and the in-group relationships of amphibamids.

The LRT confidently handles all these questions
(Fig. 1) simply by employing a wider range of taxa. Adding taxa in the LRT recovers a different origin and diversification of this clade, but agrees with the origin of frogs and salamanders. Caecilians have a separate ancestry arising from Microsauria (Fig. 1), so, “Goodbye Lissamphibia!” It’s not a monophyletic clade unless it includes a much wider gamut of taxa, including the Dissorphoidea. We looked at the origin of modern amphibians in the LRT here back in 2018.

References
Pérez-Ben CM, Schoch RR and Báez  AM 2018. Miniaturization and morphological evolution in Paleozoic relatives of living amphibians: a quantitative approach
https://doi.org/10.1017/pab.2017.22Published online: 23 January 2018
Schoch RR 2018. The putative lissamphibian stem-group: phylogeny and evolution of the dissorophoid temnospondyls. Journal of Paleontology 93(1):1-20. 0022-3360/15/0088-0906
doi: 10.1017/jpa.2018.67

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