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.
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.
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.
Compare the snake-like skull of Gymnothorax
(Fig. 2) to Boa (Fig. 4). The convergence is remarkable.
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.
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.
Some Wikipedia definitions:
- 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.
- 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.
- 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.
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…
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.
Bloch ME 1795. Naturgeschichte der ausländischen Fische. Berlin. v. 9. i-ii + 1-192, Pls. 397-429.