The moray eel: a living lobefin without lobes or fins

More heresy today
as everyone thought osteolepiform lobe-in fish, like Osteolepis, became extinct shortly after the Devonian, 360 mya. Sisters evolved into tetrapods and ray-fin fish (Fig. 7). After testing, we can talk about one more extant branch, overlooked until now.

Figure 1. Moray eel skeleton. Note the two gray dots represent absent fins.

Figure 1. Moray eel skeleton. Note the two gray dots represent absent fins. The apparent second set of jaws are gill bars able to jump forward to grab bitten prey and pull it back to the esophagus.

The moray eel
(genus: Gymnothorax; Figs. 1,2) nests between two Devonian lobefins, Gogonosus and Onychodus in the large reptile tree (LRT, 1507 taxa, subset Figs. 5,7). Gymnothorax has no lobes and no fins. Perhaps that is why it was never included in prior lobe fin taxon lists.

Many hundreds of millions of years have passed since the Devonian.
In the meantime one branch of lobefins gave rise to dinosaurs, bats, and blog readers. Another branch gave rise to most ray-fin fish. A third branch gave rise to Gymnothorax, a newly recovered rhipidistian that lost several facial bones and four fins since the Devonian. What remains is a scale-less eel with a bad reputation that would rather nest with Devonian lobe-fin rhipidistians than other tested ray-fin fish based on skeletal traits.

Figure 2. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.

Figure 2. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.

Distinct from Onychodus,
the exit nares are above the orbits, not below, running in an excavated channel anterior confluent with the orbit. The posterior skull lacks a squamosal, so the jaw muscles are present just beneath the skin, as in snakes, not covered by bone as in most lobe-fins.

FIgure 1. Several views of the Onychodus skull.

FIgure 3. Several views of the Onychodus skull. Compare to Gymnothorax in figure 2.

Compare the snake-like skull of Gymnothorax
(Fig. 2) to Boa (Fig. 4). The convergence is remarkable.

Figure 6. Boa constrictor skull from 4 angles. Note the similarities, by convergence, to the Gymnothorax skull in figure 2.

Figure 4. Boa constrictor skull from 4 angles. Note the similarities, by convergence, to the Gymnothorax skull in figure 2.

Gymnothorax afer (Bloch 1795, type genus) Gymnothorax funebris (Ranzani 1839) is the extant green moray eel, which has no limbs or fins and traditionally nests within the Teleostei. Here this 2m eel nests between the lobefins Gogonasus and Onychodus, a much more primitive node than basal Teleostei. Several cheek bones are also reduced or missing. Note the elongate torso (Fig. 1), prior to the anterior chevrons. That is a primitive trait in vertebrates.

Figure 5. Subset of the LRT with Gymnothorax added between several rhipidistian lobefins.

Figure 5. Subset of the LRT with Gymnothorax added between several rhipidistian lobefins. Note the lateral spiracle without an operculum, the exit for the gill basket.

Lately there seems to have been a lot of ‘low hanging fruit’
waiting to be metaphorically ‘plucked’ by someone willing to simply add taxa to a growing online resource. Apparently academic paleontologists have been taking the less rewarding path, using genomic studies and excluding taxa based on bias and tradition. No one wants to cross the street. Everyone stays in their yard.

As readers should know by now,
when you include taxa that have never been tested together, you invite paradigm shifts… and here it happened once again. Discovery is what makes paleontology fascinating, whether in the field with your crew, or whenever a farmer brings in a new plate and counterplate, or when you just sit at your desk and explore new possibilities on your computer monitor and Photoshop software. The fine details can be hashed out with firsthand observations. Right now paleontology needs to clean house, because the dust has settled all over.

Figure 7. GIF animation showing the dual bite of the dual jaws in moray eels. Both are derived from gill bars.

Figure 6. GIF animation showing the dual bite of the dual jaws in moray eels. Both are derived from gill bars. Note: this makes Gymnothorax one of the few fish with a neck, prior to what would have been the pectoral girdle. Seahorses are another. The external naris exit is that little pipe above the orbit. This skull is an inaccurate cartoon. The naris does not perforate the skull at midline  nor is the skull split at midpoint in reality. Compare to figure 2.

Some Wikipedia definitions:

  1. Rhipidistia (dipnotetrapodomorphs include tetrapods and lungfishes. Rhidistia formerly referred to a subgroup of Sarcopterygii consisting of the Porolepiformes and Osteolepiformes, a definition that is now obsolete.
  2. Sarcopterygii or lobe-finned fish (Crossopterygii) include bony fish and tetrapods Living non-tetrapod sarcopterygians include two species of coelacanths and six species of lungfish.
  3. Tetrapodomorpha (Choanata) are tetrapods and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Tetrapodomorph fossils are known from the early Devonian onwards, and include Osteolepis, Panderichthys, Kenichthys and Tungsenia.

The LRT (subset Fig. 7) generally puts a kink in these definitions and inclusion sets.

Figure x. Subset of the LRT focusing on fish and other basal vertebrates.

Figure 7. Subset of the LRT focusing on fish and other basal vertebrates.

Future studies
Rhizodontids, like Rhizodus and Gooloogongia, are long-bodied predatory Osteolepiformes with reduced fins and a straight tail (Fig. 8), ideal ancestors for Gymnothorax, at first glance. I will add a rhizodont skull or two to the LRT to see if this guess has any validity in the LRT. Note the jaws are rather narrow and the marginal fangs are long in Rhizodus, like those of Gymnothorax. So, this looks promising…

Figure 8. Rhizodus images appear to be transitional toward the morphology of Gymnothorax.

Figure 8. Rhizodus images appear to be transitional toward the morphology of Gymnothorax.

Despite attempts at suppressing it,
and after all the hate speech from a couple of English PhDs and their followers, the LRT continues to recover overlooked relationships that can be confirmed or refuted by simply adding taxa to existing cladograms. Parts of the LRT have been confirmed years after posting here, here and here, to start a long list. If moray eels have been associated with osteolepiformes before, please let me know so I can cite the publication.


References
Bloch ME 1795. Naturgeschichte der ausländischen Fische. Berlin. v. 9. i-ii + 1-192, Pls. 397-429.

wiki/moray eel
wiki/Rhizodontida

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2 thoughts on “The moray eel: a living lobefin without lobes or fins

  1. Is it possible for you to make your supermatrix public? I’m interested in your methods. Perhaps a link to a google drive or dropbox file easily accessible from your sites?

    • Jake, a supermatrix is a collecion of previously published (and typically uncorrected) matrices. The LRT is just a big matrix. It has been updated daily lately. My methods are posted daily at the blogsite; tracing photos, making reconstructions, scoring traits. ReptileEvolution.com is the collection of taxa in phylogenetic order, now almost 8 years old. The .nex file is available by request here: http://www.reptileevolution.com/reptile-tree.htm top right hand corner. I didn’t see a request in the comment. Let me know through the above url and you’ll get a .nex file via email. Dave

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