A second convergent origin of the three-part operculum in bony fish illustrated

As reported earlier,
in the large reptile tree (LRT, 2315 taxa) ‘bony’ fish appeared in two independent clades by convergence. The clade that later produced tetrapods began with conodonts. The clade that later produced sharks, swordfish and flounders began with placoderms.

Yesterday we looked at
the immediate appearance of the three-part operculum in tiny spiny shark placodermomorphs following tiny Mesacanthus.

Today we look at the much slower,
more gradual evolution of the three-part operculum in the clade Conodontomorpha (Fig 1). Middle Silurian Lasanius and Euphanerops (Fig 1) are primitive members lacking opercula.

Figure 1. The gradual appearance of a three-part operculum in the clade of bony fish derived from conodonts descendants. Numbers count the opercula present. ” data-image-caption=”

Figure 1. The gradual appearance of a three-part operculum in the clade of bony fish derived from conodonts descendants. Numbers count the opercula present.

” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/03/operculum-evolution_conodontomorpha588-1.jpg?w=111″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/03/operculum-evolution_conodontomorpha588-1.jpg?w=380″ class=”size-full wp-image-84876″ src=”https://pterosaurheresies.files.wordpress.com/2024/03/operculum-evolution_conodontomorpha588-1.jpg?w=584&h=1573″ alt=”Figure 1. The gradual appearance of a three-part operculum in the clade of bony fish derived from conodonts descendants. Numbers count the opercula present.” width=”584″ height=”1573″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/03/operculum-evolution_conodontomorpha588-1.jpg?w=584&h=1573 584w, https://pterosaurheresies.files.wordpress.com/2024/03/operculum-evolution_conodontomorpha588-1.jpg?w=56&h=150 56w, https://pterosaurheresies.files.wordpress.com/2024/03/operculum-evolution_conodontomorpha588-1.jpg?w=111&h=300 111w, https://pterosaurheresies.files.wordpress.com/2024/03/operculum-evolution_conodontomorpha588-1.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 1. The gradual appearance of a three-part operculum in the clade of bony fish derived from conodonts descendants. Numbers count the opercula present.

Last week
several of these taxa moved from the placoderm clade to the conodont clade – and that brought the number of MPTs way down, bringing resolution to the fish subset of the LRT. That’s the goal. The origin of the opercular elements is a key trait that lumps and splits the two bony fish clades.

Unfortunately, that origin cannot be determined by simple observation. Both bony fish clades developed 3-part opercula.

In addition to changing the colors of the opercular elements,
the traditional lacrimal in these taxa was re-identified as an anterior postorbital element.

If such a change resolves problems, be prepared to risk doing so.

According to Wikipedia,
“Current cladistic classification splits the Osteichthyes into two full classes. Under this scheme Osteichthyes is monophyletic, as it includes the tetrapods making it a synonym of the clade Euteleostomi. Most bony fish belong to the ray-finned fish (Actinopterygii).”

Tradition splits lobe-fins from ray-fins. The LRT does not confirm this hypothesis. Instead the LRT splits lobe-fins and splits ray-fins.

Zhu, Yu and Janvier 1999
titled their Early Devonian Psarolepis paper “A primitive fish sheds light on the origin of bony fishes.” Due to taxon exclusion they did not realize bony fish had two origins. In the LRT Psarolepis is a placoderm with teeth.

Zhu et al 2009
considered Late Silurian Guiyu, “The oldest articulated osteichthyan”. Due to taxon exclusion they did not realize bony fish had two origins. In the LRT Guiyu nests between traditional placoderms and catfish.

Betenacur-R et al 2013
trusted genetics and did not employ fossil taxa. They wrote, “The tree of life of fishes is in a state of flux because we still lack a comprehensive phylogeny that includes all major groups.” Due to taxon exclusion they did not realize bony fish had two origins, so their efforts were another waste of time and resources. Deep time genomic tests fail too often by recovering untenable results and ignoring fossil taxa.

Given the results of the LRT,
don’t trust the results of the LRT either. Don’t trust any results. Be a good scientist and build your own LRT to confirm, modify or reject this novel hypothesis of interrelationships.

Then let us all know what your cladogram looks like.
Remember, these are all hypotheses of interrelationships.
And we’re all here to help each other figure things out.

References
Betenacur-R et al (23 co-authors) 2013. The tree of life and a new classification of bony fishes. PLOS currents 10.1371/currents.tol.53ba26640df0ccaee75bb165c8c26288
Traquair R 1899. XXXII Report on Fossil Fishes collected by the Geological Survey of Scotland in the Silurian Rocks of the South of Scotland. Transactions of the Royal Society of Edinburgh, 39(3): 827–864.
Zhao et al (4 co-authors) 2009.
Zhu M, Yu X and Janvier 1999. A primitive fossil fish sheds light on the origin of bony fishes. Nature 397:607–610.
Zhu M, Zhao W, Jia Lu J, Qiao T and Qu Q 2009. The oldest articulated osteichthyan reveals mosaic gnathostome characters. Nature 458:469-474.

wiki/Osteichthyes