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Qingmenodus, an Early Devonian onychodontid put together from partial skulls

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Two questions arise on this blogpost:
1: Do the preserved portions of the two specimens of Qingmenodus (IVPP V 1603.5 and .6, Figs 1, 2) both preserve a pair of frontals? If so they overlap.
2: Are onychodontids sarcopterygians or palaeoniscids?

Evidence presented here indicates 1: both specimens preserve frontals, and 2: both specimens are palaeoniscids, not sarcopterygians. Both of these hypotheses are contra those of the original authors (Lu and Zhu 2009, and Lu et al 2016).

Andrews et al 2005 wrote about Onychodus (Fig 1),
More anteriorly, in the middle part of the ethmosphenoid, the cartilaginous dorsal part of the braincase was at least as deep as the ossified ventral part. This is in complete contrast to the condition in other Devonian lobe-fins, where the ethmosphenoid is not only fully ossified but so firmly fused to the skull roof that the two cannot be separated.”

“The pectoral fin is poorly known, but the right humerus of the holotype (WAM 92.2.8) is well preserved (Figs 66–68). It articulates with the well-preserved scapulocoracoid. It has two distal articulation surfaces, indicating that the pectoral fin had both a radius and an ulna. The pectoral fin apparently lacked mobility in the horizontal plane, and had only weak movement in a vertical plane unless a large cartilage pad was present at the articulation.”

“There is no deltoid process present, as seen in the Rhizodontida and Osteolepiformes.”

“The pelvic fin is poorly preserved or absent on all the specimens.”

Question 2. Are onychodontids sarcopterygians? Or palaeoniscids?
Prior authors did not mention and did not test palaeoniscids. The LRT tests both palaeoniscids and sarcopterygians along with all other fish clades. Onychodus and Strunius both nest as
basal palaeoniscids. The humerus and probable radius and ulna of Onychodus (described above by Andrews et al 2006) would then represent a third convergent appearance of lobe fins. Longtime readers may recall coelacanths are not sisters to rhipidistians in the LRT, but lungfish and Polypterus are. Much depends on how one labels those fish facial bones. That problem took half a year to resolve here. It wasn’t easy and they don’t teach that at any university, yet.

Maybe someday…

References
Andrews M, Long J, Ahlberg P, Barwick R and Campbell K 2006. The structure of the sarcopterygian Onychodus jandemarrai n. sp. from Gogo, Western Australia: with a functional interpretation of the skeleton. Transactions of the Royal Society of Edinburgh. 96 (3): 197–307.
Jessen 1966. in Piveteau (Ed.). Traite de paleontologie. Tome 4. L’origine des Vertebres, leur expansion dans les eaux douces et le milieu marin. Vol. 3. Actinopterygiens, Crossopterygiens, Dipneustes. Masson & Cie, Paris
Lu J and Zhu M 2009. An onychodont fish (Osteichthyes, Sarcopterygii) from the Early Devonian of China, and the evolution of the Onychodontiformes. Proceedings of the Royal Society B doi:10.1098/rspb.2009.0708 Published online.
Lu J et al 2016. A Devonian predatory fish provides insights into the early evolution of modern sarcopterygians. Science Advances 2(6):e1600154, doi:10.1126/sciadv.1600154


Source: https://pterosaurheresies.wordpress.com/2023/06/24/qingmenodus-an-early-devonian-onychodontid-put-together-from-partial-skulls/


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