Palaeospondylus rebuttal from Brownstein 2023

Saturday, January 20, 2024 13:15

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As we learned earlier,
and Brownstein 2023 wrote, “Palaeospondylus gunni isa Middle Devonian vertebrate from Scotland whose affinities to other vertebrates have remained controversial over more than 130 years of study.”

In 2022 the LRT nested Devonian Palaeospondylus with rays and gave rise to a larger manta-like Cretaceous fish, Aquilolamna (Fig 2), but only in the LRT, at present.

Figure 1. A specimen of Palaeospondylus in situ with colors added here. This appears to be a ray in the hammerhead shark, Sphyraena family.

Brownstein 2023 wrote,
“Proper taxon sampling is key for resolving the position of problematic fossils and can completely change their positions on the Tree of Life.”

Good to have someone else also say that, too.

“Hirasawa et al. only analysed †P. gunniin a tetrapodomorph-centric matrix2, meaning that placements withinlungfishes or outside lobe-finned fishes altogether favoured for overa century5–7 were not actually tested in their study.”

“To test the hypothesis that †P. gunni is a pan-tetrapod, I used thecomputed tomography data and descriptions provided by Hirasawaet al.4 to include this taxon in the dataset from Brazeau et al.8, whichincludes 95 pan-gnathostomes spanning all major clades coded for 284 characters.”

So Brownstein did not test rays and blamed, “The incompleteness of †P. gunni drives the formation of a polytomy.” I would blame taxon exclusion. Don’t let THAT happen to you.

Figure 2. Aquilolamna in situ from Vullo et al. 2021. Colors added here.

That’s why the LRT tests a much wider gamut of taxa
in order to not shut out any corner of the vertebrate family tree from consideration and candidacy in interrelationships, especially of enigma taxa like Palaeospondylus (Fig 1).

References
Brownstein CD 2023. Palaeospondylus and teh early evolution of gnathostomes. Nature Matters arising. https://doi.org/10.1038/s41586-023-06434-5
Hirasawa T, Oisi Y and Kuratani S 2016. Palaeospondylus as a primitive hagfish. Zoological Letters. 2 (1): 20.
Hirasawa T, Hu Y, Uesugi, K. et al. 2022. Morphology of Palaeospondylus shows affinity to tetrapod ancestors. Nature https://doi.org/10.1038/s41586-022-04781-3
Hutton FW 1872. Catalogue with diagnoses of the species. Ed. Hutton, FW and Hector J (eds), Fishes of New Zealand, pp. 1-88 pls 1-12, Colonial Museum and Geological Survey Department, Wellington.
Joss J and Johanson Z 2007. Is Palaeospondylus gunni a fossil larval lungfish? Insights from Neoceratodus forsteri development. J Exp Zool B Mol Dev Evol. 2007 Mar 15;308(2):163-71. https://pubmed.ncbi.nlm.nih.gov/17068776/
Johanson Z et al. 5 co-authors 2017. Questioning hagfish affinities of the enigmatic Devonian vertebrate Palaeospondylus. Royal Society Open Science. 4 (7): 170214.
Smith A 1829. Descriptions of new, or imperfectly known objects of the animal kingdom, found in the south of Africa. South African Commercial Advertiser 3: 2.
Thomson KS 2004. A Palaeontological Puzzle Solved?. American Scientist. 92 (3): 209–211.
Thomson KS, Sutton M and Thomas B 2004. A larval Devonian lungfish. Nature 426(6968):833-834.
Traquair RH 1890. On the fossil fishes at Achanarras Quarry, Caithness. Ann Mag
Nat Hist 6th Ser. 1890;6:479–86.
Vullo R, Frey E, Ifrim C, Gonzalez Gonzalez MA, Stinnesbeck ES and Stinnesbeck W 2021. Manta-like planktivorous sharks in Late Cretaceous oceans. Science 371(6535): 1253-1256. DOI: 10.1126/science.abc1490