Short-faced, big-eyed taxa at the base of all bony fish

The origin of bony fish 
is a traditional enigma. Apparently no one before the LRT derived bony fish from specific hybodontid sharks. Perhaps this is so due to a lack of effort. Evidently no prior workers applied tetrapod homologs to all vertebrate skulls, including sharks and sturgeons. Applying those homologs was required here in the large reptile tree (LRT) in order to score all taxa using a common set of traits.

According to Arratia 2010,
“Traditionally, fossils have played little role in most studies of the phylogenetic relationships of teleosts. The usual approach is to study only recent fishes and when fossils are considered their position is assumed in the cladogram. During the last few years this approach has been challenged by the inclusion of both fossil and recent species in phylogenetic studies.”

Unfortunately Arratia did not include enough fossil species. No sharks, No placoderms. No spiny sharks. No placoderms. No Gregorius (Fig. 1).

According to Arratia 2010,
“When fossil and recent taxa are included in phylogenetic analyses, the elopomorphs stand as the most plesiomorphic group among extant teleosts.”

Elopomorphs are not basal bony fish in the LRT where more taxa are included. Prohalecites (Fig. 1) and spiny sharks like Homalacanthus (Fig. 1) are basal taxa to their respective bony fish clades following the first great dichotomy of bony fish. Gregorius (Fig. 1) is their last common ancestor (LCA). Note the shorter rostrum and large eyes close to the anterior margin are juvenile traits retained into adulthood, as we discussed earlier.

Figure 1. Gregorius descends from Hybodus, the shark and is ancestral to Prohalecites at the base of the ray-fin bony fish. Gregorius is also ancestral to Homalacanthus at the base of the spiny sharks leading to lobefins, placoderms, catfish and a variety of other taxa.

Figure 1. Gregorius descends from Hybodus, the shark and is ancestral to Prohalecites at the base of the ray-fin bony fish. Gregorius is also ancestral to Homalacanthus at the base of the spiny sharks leading to lobefins, placoderms, catfish and a variety of other taxa. See figure 2 for a to scale view.

Figure 2. Representatives from the Early Devonian radiation that gave us bony fish, including Prohalecites and Homalcanthus.

Figure 2. Representatives from the Early Devonian radiation that gave us bony fish, including Prohalecites and Homalcanthus. Harpagofututor is close to living moray eels.

A short face and large orbit
characterize both branches of basal bony fish in the LRT, derived from Gregorius, a late survivor ion  the Late Carboniferous of an Late Silurian radiation.

Figure 1. Taxa from the LRT on one branch of the bony fish. Doliodus is one of these.

Figure 3. Taxa from the LRT on one branch of the bony fish. Doliodus is one of these.

Figure 1. Click to enlarge. Acanthodians and their spiny and non-spiny relatives in the LRT (subset Fig. 2), not to scale.

Figure 4. Acanthodians and their spiny and non-spiny relatives in the LRT (subset Fig. 2), not to scale.

Due to taxon exclusion,
Arratia 2010 lists the moray eel, Gymnothorax, and the gulper eel, Eurypharynx (Fig. 5), as elopomorphs. By contrast, when more taxa are added, as in the LRT, both nest closer to Gregorius and hybodontid sharks, both basal to the bony fish first dichotomy.

Figure 6. Eurypharynx evolution. This clade split from Gregorius prior to the major split in bony fish.

Figure 5. Eurypharynx evolution. This clade split from Gregorius prior to the major split in bony fish.

Some taxa (e.g  spiny sharks) at basal nodes in the LRT
are not mentioned by Arratia 2010. Some elops relatives (e.g. the swordfish, Xiphias) are not mentioned by Arratia 2010. Osteoglossum (Fig. 6) nests in the other bony fish clade, the one that includes placoderms, catfish, lobe fins and spiny sharks, and not at the base.

Figure 1. The arowana, an Amazon River predator, nests with Late Jurassic Dapedium in the LRT.

Figure 6. The arowana, an Amazon River predator, nests with Late Jurassic Dapedium in the LRT.

After spending several months 
with ninety+ ray fin fish, trying to shuffle and reshuffle them into their evolutionary order in the LRT (correcting hundreds of mistakes along the way) only a relative few LRT characters turn out to be important for lumping and splitting bony fish. And many of these recur as reversals and convergent trait, making the task more difficult.

  1. Orbit close to the tip of the rostrum, in the middle of the skull vs. close to the rear margin. Sometimes a sword can lengthen the rostrum
  2. Sagittal crest or not
  3. Maxilla either with teeth and a butt joint with the premaxilla, or loosely overlapping the premaxilla without teeth, or other variations
  4. Circumorbital bones absent, or present as a gracile ring, or present as large plates extending toward the preopercular, or as a gracile ring extending to the preopercular
  5. Rostral profile convex or cornered or straight or concave
  6. Coracoid short or long or essentially absent
  7. Parietals meet medially or split by an intervening postparietal
  8. Naris separate from the orbit or confluent
  9. Etc., etc.

Earlier we looked at the various radiations of bony fish
from a variety of spiny sharks in their ancestry (Fig. 4). Since then more taxa have been added, especially on the ray-fin clade. Please see the LRT for the latest cladogram.


References
Arratia G 2010. Critical analysis of the impact of fossils on teleostean phylogenies, especially that of basal teleosts. In: Morphology, Phylogeny and Paleobiogeography of Fossil Fishes Elliott DK, Maisey JG, Yu X and Miao D (eds.): pp. 247-274, 15 figs., 6 tabs. Verlag Dr. Friedrich Pfeil, München, Germany – ISBN 978-3-89937-122-2

https://pterosaurheresies.wordpress.com/2020/05/08/an-unexpected-resolution-to-the-spiny-shark-problem/

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