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The extant bowfin (Amia) finally has a Middle Devonian sister

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Such a discovery was expected.
As everyone knows, basal taxa in a cladogram are phylogenetically tied to deep time ancestors, even if  those ancestors are unknown and/or those descendants are late surviving extant species.

In Dr. John Long’s (1995 ed) popular book,
‘The Rise of Fishes’, on page 140 is an Middle Devonian Old Red Sandstone fish from Scotland labeled Cheirolepis (Fig. 1). In counterpoint, a reconstruction and scoring nests this specimen with the extant bowfin (Amia), the most primitive tested teleost in the large reptile tree (LRT, 1655+ taxa).

Figure 1. Middle Devonian Proamia in situ and reconstructed using DGS methods. Compare to Amia in figure 2.

Now I wonder
if ‘Cheirolepis‘ has become a wastebasket taxon for all fish of this age. I also wonder which of the many published ‘Cheirolepis‘ specimens is the holotype? It was first described by Agasssiz 1835.

Figure 2. Skeleton of the extant bowfin (Amia).

Every taxon needs a unique name
and this one doesn’t have one (that I know of, queries have been presented to museum curators) so ‘Proamia’ will be used here and in the MacClade file until a real name is recovered or established.

Figure 3. Proamia skull reconstructed using DGS methods. Preoperculum and operculum elements separated from the background elements by shadows. Compare to Amia skull in figure 4.

Relatively little has changed
between Proamia (Fig. 1) and Amia (Fig. 2). Figure 4. Skull of the extant bowfin (Amia). Compare to figure 3.Ancestors include
GregoriusProtosphyraena and Pachycormus. The dorsal fin expands anteriorly. The caudal in loses its Y-shape in favor of an elliptical shape. Post-cranial bones become better ossified. The teeth become thinner and more numerous. The jugal and postorbital become more ossified.

Figure x. Subset of the LRT focusing on basal vertebrates (= fish).

Careful cladogram readers will note
Polydactylus, the threadfin (Fig. 5), now nests with sea robins, like Prionotus after the realization that Polydactylus also has that pseudo-lacrimal shield beneath the orbit created by the laterally exposed palatine that other clade members share. And now we know how the sea robin got its ‘fingers’. They arise from the coracoid in threadfins.

Figure 5. Polydactylus skull from Gregory 1938 colored here with tetrapod homologs.


References
Agassiz JLR 1835. Recherches sur les Poissons fossiles, 5 volumes. Imprimerie de Petitpierre et Prince, Neuchaatel, 1420 pp.


Source: https://pterosaurheresies.wordpress.com/2020/02/29/the-extant-bowfin-amia-finally-has-a-middle-devonian-sister/


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