Origin and evolution of the Cynodontia 2024

Pusch et al 2024 wrote,
“The origin of cynodonts, the group ancestral to and including mammals, is one of
the major outstanding problems in therapsid evolution. One of the most troubling
aspects of the cynodont fossil record is the lengthy Permian ghost lineage between
the latest possible divergence from its sister group Therocephalia and the first
appearance of definitive cynodonts in the late Permian.”

The Pusch team produced a cladogram
(Fig 1) after studying several skulls inside and out using µCT scans, adding their own DGS colors. They wrote, “Cynognathia—Although represented by only two taxa in our analyses, this clade is well-supported. We did not sample Cynognathus itself.”

Seems odd, a paper focusing on ‘Cynodontia’ omitting Cynognathus (Fig 2).

Figure 1. Cynodont cladogram from Pusch et al 2024. Colors added here represent taxa tested in the LRT and TST. ” data-image-caption=”

Figure 1. Cynodont cladogram from Pusch et al 2024. Colors added here represent taxa tested in the LRT and TST.

” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/03/cynodont.cladogram.puschetal2024-588.jpg?w=210″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/03/cynodont.cladogram.puschetal2024-588.jpg?w=584″ class=”size-full wp-image-84858″ src=”https://pterosaurheresies.files.wordpress.com/2024/03/cynodont.cladogram.puschetal2024-588.jpg?w=584&h=834″ alt=”Figure 1. Cynodont cladogram from Pusch et al 2024. Colors added here represent taxa tested in the LRT and TST.” width=”584″ height=”834″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/03/cynodont.cladogram.puschetal2024-588.jpg?w=584&h=834 584w, https://pterosaurheresies.files.wordpress.com/2024/03/cynodont.cladogram.puschetal2024-588.jpg?w=105&h=150 105w, https://pterosaurheresies.files.wordpress.com/2024/03/cynodont.cladogram.puschetal2024-588.jpg?w=210&h=300 210w, https://pterosaurheresies.files.wordpress.com/2024/03/cynodont.cladogram.puschetal2024-588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 1. Cynodont cladogram from Pusch et al 2024. Colors added here represent taxa tested in the LRT and TST. Note the absence of Cynognathus. (B) represents the origin of the Cynodontia. I do not know if unduplicated tested taxa are represented by more or less complete material or just scraps.

Cynodonts were tested earlier
(1) in the large reptile tree (LRT) and (2) in the therapsid skull tree (TST). Pusch et al used a larger number of basal cynodont taxa. The LRT used more outgroup and ingroup taxa. Results were similar with regard to taxa tested in both studies. Cynognathus (Fig 2) nests with Thrinaxodon and Procynosuchus in both the LRT and TST.

Figure 3. Cynognathus reconstructed and restored from related taxa.

” data-image-caption=”

Figure 3. Cynognathus reconstructed and restored from related taxa.

” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2022/09/cynognathus-recon588.jpg?w=209″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2022/09/cynognathus-recon588.jpg?w=584″ class=”size-full wp-image-71818″ src=”https://pterosaurheresies.files.wordpress.com/2022/09/cynognathus-recon588.jpg?w=584&h=840″ alt=”Figure 3. Cynognathus reconstructed and restored from related taxa.” width=”584″ height=”840″ srcset=”https://pterosaurheresies.files.wordpress.com/2022/09/cynognathus-recon588.jpg?w=584&h=840 584w, https://pterosaurheresies.files.wordpress.com/2022/09/cynognathus-recon588.jpg?w=104&h=150 104w, https://pterosaurheresies.files.wordpress.com/2022/09/cynognathus-recon588.jpg?w=209&h=300 209w, https://pterosaurheresies.files.wordpress.com/2022/09/cynognathus-recon588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

The authors wrote,
“the stratigraphically earliest cynodonts Abdalodon diastematicus and Charassognathus gracilis) at the base of Cynodontia.”

The authors recovered those two genera at the base of the inclusive clade Cynodontia (Fig 1), which also includes Mammalia.

Pusch et al concluded,
“Our phylogenetic analyses support the general idea of therocephalian paraphyly previously recovered by Abdala (2007), Botha et al. (2007), and Abdala et al.
(2019), but in the context of a novel and stratigraphically more congruent topology in which cynodonts and eutherocephalians are sister-taxa to the exclusion of “basal therocephalians.”

The LRT recovers cynodont ancestors back to Ediacaran worms. The TST includes many therocehalians. The latter nests Charassognathus and Abdalodon outside the Cynodontia. Both include Procynosuchus at the base of the Cynodontia. The TST nests Dvinia within the Cynodontia, but closer to Pachygenelus + mammals. Pachygenelus does not appear in the Pusch et al cladogram (Fig 1).

Those two omissions (Cynognathus and Pachygenelus) may explain the small differences in the two cladograms, one done with µCT scans vs one without.

References
Pusch LC, Kammerer CF and Fröbisch J 2024. The origin and evolution of Cynodontia (Synapsida, Therapsida): Reassessment of the phylogeny and systematics of the earliest members of this clade using 3D-imaging technologies. The Anatomical Record Special Issue Article DOI: 10.1002/ar.25394

wiki/Cynodontia