The little noticed connection between swordfish and gars

Gars are traditionally considered primitive fish.
We invalidated that earlier when the clade Holostei was dismantled by the LRT and even earlier when the LRT nested the garfish (Lepisosteus, Fig. 3) with sticklebacks and sea horses.

In the large reptile tree (LRT, 1516 taxa, subset Fig. 1) swordfish and gars are sister taxa at the base of the seahorse clade, derived from the barracuda clade. Swordfish and gars seem to differ quite a bit from one another, but currently there are no tested transitional taxa between them.

Figure 1. Subset of the LRT focusing on ray fin fish and showing a hatchling swordfish and an adult gar.

Figure 3. Subset of the LRT focusing on bony ray fin fish and kin. Here Devonian Cheirolepis nests with extant deep sea Malacosteus. More taxa here. The flying fish, Exocoetus, nests with the swordfish, Xiphias, close to Lepisosteus, the gar.

No one has ever put gars and swordfish together before.
Because they really do not look alike overall (Figs. 1, 2). Someday some taxon might come between them, but presently none do.

Figure 2. Extant swordfish (Xiphias) to scale with Eocene swordfish (Blochius). Note the longer, more gracile swordfish ancestor, Blochius.

It might help
if you saw a swordfish (Xiphias) hatchling which has two elongate jaws with teeth (Figs. 3,4), not just a toothless sword and toothless mandible as seen in the adult (Fig. 2).

Figure 3. Adult gar fish (Lepisosteus) compared to look-alike swordfish (Xiphias) hatchling.

The Florida Museum reports,
“Gars are slow growing fishes that are relatively long lived. Newly hatched gars are 8 to 10 mm in length. Hatchlings attach themselves to vertically to submerged objects by an adhesive disc on their snout. Young remain attached by the adhesive disc until the yolk sac is absorbed (about 9 days). After the absorption of the yolk sac the young are able to remain horizontal, take their first aerial breath and begin feeding.”

Xiphias gladius (Linneaus 1758; Gregory and Conrad 1937; up to 4.5m in length) is the extant swordfish, derived from the barracuda, Sphyraena. 1cm long hatchlings more closely resembled little barracudas, then little sailfish before reducing the long dorsal fin. The sword is not used to spear, but to slice and maim smaller fish traveling in schools. The pelvic fins are absent. Larger females produce more eggs, up to 29 million.

Lepidosteus osseus (also Lepisosteus Lacepéde 1803) is the extant longnose gar. Note the jaw joint is in front of the orbit, similar to the stickleback, Gasterosteus. The longest teeth arise from the inside the of jaws, the long vomer. The rostrum is lined by the premaxilla. The maxilla is absent. The traditional jugal is the lacrimal.

First impressions can be misleading.
Score the traits and let the software nest the taxa. If there are no closer sisters, two apparently distinct taxa can nest together.

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References
de Lacepéde BG 1803. Histoire naturelle des poissons. Tome Cinquieme. 5(1-21):1-803 + index.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/lepisosteus-osseus/

The primitive arowana (Osteoglossum) enters the LRT

Osteoglossum formosum (Cuvier 1829; up to 2m in length; Figs. 1, 2) is the extant arowana or bonytongue. A facultive air breather, the slow-moving, heavily-scaled arowana feeds on prey just above the water. Fossils extend back to the Late Jurassic. The pelvic fins are reduced to strands. In the large reptile tree (LRT, 1516 taxa, Fig. 3), Osteoglossum nests with Early Jurassic Dapedium.

Figure 1. The arowana, an Amazon River predator, nests with Late Jurassic Dapedium in the LRT. The pink dot indicates the position of the pelvic fins, absent in the skeleton below, present in the specimen above.

I hope the DGS colors added to these fish skulls
make them more accessible for learning. Consider this a starting point on your own academic journey and learn as much as you can on your own.

FIgure 2. Osteoglossum skull with colors added to identify bones.

And if you ever wanted to swim with a Jurassic fish,
you don’t have to start with a drop of blood from a mosquito. Just jump into the Amazon, the Nile or any of the rivers of Borneo and Western Australia. Prior to the split of these exclusively freshwater fish, all these areas were united at Pangaea and Gondwana.

For that matter
the walking catfish (Clarias) will take you back to the Silurian (430 mya), and it will get out of the water to walk with you! Or the headless lancelet (Amphioxous) will take you back to the Cambrian (550mya), about as far back as swimming chordates go.

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References
Cuvier GCLD 1829. Le Règne Animal distribué d’apres son organisation, pour servir de base a l’histoire naturelle des animaux et d’introduction a l’anatomie comparée. Avec figures dessinées d’après nature. Nouvelle édition, revue et augmentée. Tome V. Suite et fin des Insectes. Par M. Latreille. Déterville & Crochard, Paris, i-xxiv + 556pp.

The reason the freshwater fish arowana live across the sea

wiki/Dapedium
wiki/Osteoglossum
wiki/Arowana

New origin of dinosaurs video by Dr. Sterling Nesbitt

There’s a new YouTube video
featuring Dr. Sterling Nesbitt describe his version of dinosaur origins.

Unfortunately
Dr. Nesbitt ‘pulls a Larry Martin‘ by concentrating on key dinosaurian traits and not concentrating on the last common ancestor (Fig. 2) in a wide gamut phylogenetic analysis, like the large reptile tree (LRT, 1515 taxa, subset Fig. 3). Nesbitt is great at finding bones in the field, and describing new taxa, but Nesbitt 2011 and Nesbitt 2017 omitted key proximal outgroups to the Dinosauria (Figs. 2, 3) and so he keeps missing ‘the big picture.’

Continuing an invalid tradition
Dr. Nesbitt nests the tropidosuchid proterochampsid, Lagerpeton, as a close dinosaur outgroup. He also nests pterosaurs close to the base of the Dinosauria, which has been a big mistake for nearly 20 years. Dr. Nesbitt omits bipedal crocodylomorphs (Figs. 2, 3) from his dinosaur cladograms, another traditional academic mistake.

Nesbitt’s taxon exclusion issues
are repaired in the LRT (subset Fig. 3) where the last common ancestor of every included taxon back to Silurian fish is documented and validated by minimizing taxon exclusion.

Figure 2. The origin of dinosaurs to scale in the LRT. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

Figure 1. Revision to the LRT with a focus on the Archosauria. Here taxa with a long carpus all nest within the Crocodylomorpha, following traditional thinking. Dinosaur outgroups are reduced. PVL 4597 is still the basalmost archosaur.

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References
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bull. Am. Mus. Nat. Hist. 352, 1–292.
Nesbitt et al. 2017. The earliest bird-line archosaurs and the assembly of the dinosaur body plan. Nature (online here).

https://pterosaurheresies.wordpress.com/2017/04/13/teleocrater-a-sister-to-yarasuchus-not-the-earliest-bird-line-archosaur/

https://pterosaurheresies.wordpress.com/2018/02/22/redefining-what-makes-a-dinosaur/

Goodbye to another traditional clade: ‘Holostei’

‘Holostei’ is a traditional clade with just a few members,
(Figs. 1-4) now widely scattered in the large reptile tree (LRT, 1515 taxa; Fig. 5). Two are extant. They are considered midway or transitional between sharks (with no bones) and bony fish (with bones).

Figure 1. Taxa that make up the traditional but invalidated clade, Holostei include Lepisosteiformes, Ammiformes and the Triassic Polidophorus. They don’t look alike here and they appear in distinct clades in the LRT. Image from Encyclopedia Brittanica needs to be updated.

According to Wikipedia
“Holostei are eight species divided among two orders, the Amiiformes (the bowfin Amia calva) and the Lepisosteiformes (the garpike Lepisosteus).” Encyclopedia Brittanica added the Triassic xx, Pholidophorus (Fig. 2).

Figure 2. Pholidophorus in situ + two skull drawings relabeled with tetrapod names.

Pholidophorus sp. (Agassiz 1832; Middle-Late Triassic; 40cm long) was a herring-like fish with primitive ganoid scales and poorly ossified spine. Traditionally considered an early teleost, with large eyes, here it nests with Late Devonian Strunius, but lacks the central posterior process of the tail. Here the skull bones are re-identified with tetrapod labels. The pectoral and pelvic fins were similar in size. This iconic fish shape is indeed plesiomorphic for ray-fin fish according to the LRT.

Figure 3. Cladogram from wiki/Holostei showing traditional interrelationships among other vertebrate taxa. In the LRT bichirs nest with lungfish, sturgeons with ratfish.

My guess is
taxon exclusion is once again the culprit, followed closely by ‘Pulling a Larry Martin‘, followed more distantly by a lack of consistency in skull bone names. Here (Fig. 2) fish skull bones are colored as homologs to tetrapod skull bones, a long needed suggestion first promoted by Schultze 2007.

Though distinct in overall appearance,
traditional members of the Holostei are united by a few traits. The late Dr. Larry Martin was famous for challenging the nesting of taxa based on a few traits, because most traits can also be found elsewhere on the family tree by convergence. In the LRT hundreds of traits nest every taxon, reducing the influence of convergence and exposing the convergence that appears in traditional Holostei.

Figure 4. Cladogram of the Pachydormidae and outgroups among traditional Holostei (yellow boxes) from Wikipedia

The LRT tree topology
is distinctly different from prior cladograms. It has a wider gamut than in figure 4, but does not include as many partial or poorly known taxa. Note the disbursement of Amia, Pholidophorus and Lepisosteus.

Figure 4. Subset of the LRT focusing on fish. Note the traditional members of the Holostei do not nest together here largely because they don’t look alike, but more like other, more attractive taxa.

Amia calva (Linneaus 1766; up to 70cm in length) is the extant bowfin, a basal fish related to gars, able to breathe both water and air. Rather than two dorsal fins, an single elongate undulating fin is present. Hatchlings look like tadpoles or miniature placoderms. The squamosal an quadratojugal are absent. The postfrontal is fused to the frontal + parietal. In contrast, the lacrimal and jugal break apart into several bones. Females produce 2000 to 5000 eggs. Fossil relatives of Amia have a worldwide distribution in fresh and salt waters.

Lepisosteus osseus (Lacepéde 1803) is the extant longnose gar. Note the jaw joint is in front of the orbit, similar to the stickleback, Gasterosteus. The longest teeth arise from the inside the of jaws, the long vomer. The rostrum is lined by the premaxilla. The maxilla is absent. The traditional jugal is the lacrimal. Compare Lepisosteus with the juvenile swordfish, Xiphias, which nests as a sister and shares many traits, including long toothy jaws and an elongate body.

Wikipedia reports,
“The thick ganoid scales of the gars are more primitive than those of the bowfin.” That is refuted by the LRT, which nests gars as derived taxa along with sticklebacks, pipefish and seahorses, all of which have a bony elements in the dermis.

Wikipedia reports,
“The spiracles are reduced to vestigial remnants and the bones are lightly ossified.” In derived fish with external skeletons, like the placoderms, sturgeons, puffers, gars and seahorses, the internal skeletons tend to be poorly ossified.

This is not the first time the LRT has split apart traditional clade members.
Over the last eight years the LRT invalidated several other traditional clades including Ornithodira, Parareptilia, Cetacea, Pinnipedia, Pterodactyloidea, Monofenestra, Scrotifera, Euarchontaglires, Scandentia, Pseudosuchia, Notoungulata, etc. This is what a wide gamut phylogenetic analysis can do. Links to the above traditional clades can be accessed by using the ‘keywords’ box above.

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References
Agassiz L 1832. Untersuchungen über die fossilen Fische der Lias-Formation. Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde, 3, 139–149.
de Lacepéde BG 1803. Histoire naturelle des poissons. Tome Cinquieme. 5(1-21):1-803 + index.
Friedman M, Shimada K, Martin LD, Everhart MJ, Liston J, Maltese A and Triebold M 2010. 100-million-year dynasty of giant planktivorous bony fishes in the Mesozoic seas. Science. 327 (5968): 990–993.
Linneaus C von 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. pp. 1–532. Holmiæ. (Salvius)
Schultze H-P 2008 (2007). Nomenclature and homologization of cranial bones in actinopterygians. Nomenclature and homologization of cranial bones in actinopterygians. In Mesozoic Fishes 4 – Homology and Phylogeny. Editors: Arratia G, Schultze H-P and MVH Wilson, Verlag Dr. F. Pfeil.

wiki/Holostei
wiki/Amiiformes
wiki/Lepisosteiformes
wiki/Pachycormiformes
wiki/Lepidosteus
wiki/Amia
wiki/Pholidophorus

eptileevolution.com/cheirolepis.htm
reptileevolution.com/amia.htm
reptileevolution.com/gasterosteus.htm

Mola mola enters the LRT

Unbelievable and unforgettable.
The ocean sunfish (Mola mola; Linneaus 1758; 4.3m tall and 3m long; Fig. 1) nests traditionally and in the large reptile tree (LRT, 1512 taxa) with the pufferfish. Both are traditional members of the order Tetraodontiformes.

Figure 4. Mola mola is a relative of Diodon in the LRT. It has no circumorbital bones, but as a hatchling has pufferfish proportions and spines.

This slow-moving surface predator
eats small fish, fish larvae, squid and floating crustaceans. The dorsal and anal fins provide propulsion, as in the pufferfish, Diodon.

According to Wikipedia,
“The fish develop their truncated, bullet-like shape because the back fin, with which they are born, never grows. Instead, it folds into itself as the creature matures, creating a rounded rudder called a clavus.” (Fig. 1)

“Their teeth are fused into a beak-like structure, and they are unable to fully close their relatively small mouths.”

“Females of the species can produce more eggs than any other known vertebrate,[3] up to 300,000,000 at a time.”

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References
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Diodon
wiki/Tetraodontidae
wiki/Ocean_sunfish
wiki/Mola_(fish)

 

Diodon, the pufferfish, enters the LRT

Diodon the pufferfish
(Fig. 1) offers a vexing problem for phylogenetic scoring. Are those facial spines transformed from circumorbital bones? Ore are they novel dermal ossifications?

Figure 1. Diodon the pufferfish offers a problem. Are those facial spines circumorbital bones? Ore are they novel dermal ossifications?

The two cheek spines
are placed like the lacrimal and jugal in the bowfin Amia (Fig. 2).

FIgure 3. The bowfin, Amia calva, is basal to both the electric eel and halibut in the LRT.

On the other hand,
a traditional sister taxon, Mola mola (Fig. 4), does not have circumorbital bones. As a hatchling Mola has pufferfish proportions and spines. So in the large reptile tree (LRT, 1514 taxa, Fig. 5) the spines of the pufferfish were not scored as circumorbital bones. And the ocean sunfish is an overgrown puffer!

Figure 4. Mola mola is a relative of Diodon in the LRT. It has no circumorbital bones, but as a hatchling (upper left) has pufferfish proportions and spines.

Pufferfish are traditional members of the Tetraodontiformes
which traditionally nest with Perciformes using genomic scores. That nesting is confirmed by the LRT.  Hughes et al. 2018 nested highly derived Tetraodontiformes with highly derived Lophiformes (angler fish). In the LRT, these clades are also related, though other taxa are closer.

Diodon sp. (Linneaus 1758) is the extant porcupinefish. The teeth are extremely tiny, lining or (perhaps due to tooth fusion), creating beak-like jaws. The spines are distributed all over the body and skull. Pelvic fins are absent. The tail is reduced. The pectoral fins provide thrust distinct from Mola. I do not see dorsal ribs inside the spines (Fig. 1). If present, they would presumably restrict the pufferfish’s ability to expand to a balloon like shape as it fills with water or air when threatened.

FIgure 5. Teleost (bony fish) cladogram. Diodon nests with Mola here. Gymnothorax is the moray eel.

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References
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Amia
wiki/Diodon
wiki/Tetraodontidae
wiki/Mola

Electric eels and anglerfish? They don’t look similar…

Updated January 15, 2021
with the addition of more taxa the electric eel nests with the bowfin, Amia, while the goosefish, Lophius, nests with the tripod fish, Bathypterois.

…and yet
the large reptile tree (LRT, 1514 taxa; subset Fig. 4) continues to nest Electrophorus and Lophius together with every additional fish taxon ever since they entered the LRT, not quite on the same day, but close.

Either something is wrong…
or something is right. These two are such odd bedfellows. Why do they continue to attract one another. My curiosity was raised, so I dived into the candidate sister taxon list!

Traditionally
catfish, like Clarias, have been associated with the electric eel, Electrophorus, but the LRT separates them by a great morphological gap, as we learned earlier here.

There is an electric catfish
with small eyes, thick lips and a cylindrical body. Unfortunately, Malapterurus is indeed a catfish, not close or even transitional to Electrophorus.

Figure 1. The goosefish Lophius in vivo. The pelvic fins are hidden from view beneath the large pectoral fins. This does not look much like an electric eel, but the two nest together in the LRT. Let’s search for a suitable, reasonable and valid transitional taxon. The inset hatchling goosefish does not provide a clue to the identity of the transitional taxon.

Figure 1. Bathypterois, the deep sea tripod fish, shown with diagram of jaws and palate from Sulak 2006, then colored and matched to the in vivo specimen.

At times like this
my guess is to go looking for a long, narrow angler fish relative (if there is one) to bridge the morphological gap that currently separates the wide-mouth goosefish, Lophius (Fig. 1), from its elongate LRT sister, the electric eel Electrophorus (Fig. 2).

It turns out a good candidate 
is Forbesichthys (Fig. 2; Putnam, 1872; 9cm in length) the spring cave fish of Missouri, USA. Yes, that’s a long way from the Amazon, where Electrophorus is found, AND a long way from both sides of the North Atlantic, where Lophius is found.

de Santana, Vari and Wosiacki 2013 determined
“that Electrophorus possesses a true caudal fin formed of a terminal centrum, hypural plate and a low number of caudal-fin rays.”

Figure 2. Forbesichthys an apparent sister taxon to Electrophorus along with other sisters to the blind cave fish, Typhlichthys subterraneus. When I find skull material for Forbesichthys, I will enter it in the LRT. That’s the mandible of Typhlichthys superimposed on the skull of the electric eel, the only comparable data at present. Image from Armbruster, Niemiller and Hart 2016.

Figure 1. Amia juvenile with DGS colors added. Image from Digimorph.org and used with permission.

Unfortunately skull material for Forbesichthys agassizii
cannot be located at present, so its addition to the LRT will have wait until those data arrive. Wikipedia reports, “The head is sloped, and it has a protruding lower jaw” similar to the electric eel. “It has a well-developed sensory system. This system occurs in clusters on the head.” Like the electric eel, eyesight is poor in all cave fish, many of which are not related to Forbesichthys. Note the similar arrangement of all fins on cave fish (Fig. 2) to the goosefish (Fig. 1).

Figure 3. Electrophorus, the electric eel, in vivo from de Santana et al. 2013.

Radiation and distribution
Given the present phylogenetic topology, the last common ancestor of Forbesichthys, Lophius and Electrophorus was in North American rivers before some descendants radiated along the coast to South America, while still others radiated along the perimeter of the then reduced North Atlantic. That primitive last common ancestor probably looked like Forbesichthys and sought dark and murky environments that it was already suited to. Both goosefish and electric eels are clearly derived.

I’m not sure how cave fish got into caves
in the first place, or how many thousands or tens of millions of years they have been there, but cave fish probably arrived from nearby rivers and lakes seeping into limestone fissures a long time ago, given that their non-cave sisters no longer inhabit North American lakes and rivers. (Let me know if this is incorrect!)

Figure 3. Revised subset of the LRT focusing on ray fin fish and kin.

Interesting factoid:
Many cave fish are cannibals, not only to sustain themselves in low prey environments, but also to avoid overpopulating such environments.

Further updates will come
if and when skull data for Fobesichthys arrives.

If anyone knows
that this hypothesis of relationships was published earlier, please cite the reference and let me know so I can provide proper credit.

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References
Armbruster JW, Niemiller ML and Hart PB 2016. Morphological Evolution of the Cave-, Spring-, and Swampfishes of the Amblyopsidae (Percopsiformes). Copeia 194(3):763–777,
deSantana CD, Vari RP and Wosiacki 2013. The Untold Story of the Caudal Skeleton in the Electric Eel (Ostariophysi: Gymnotiformes: Electrophorus). PLoS ONE 8(7): e68719. https://doi.org/10.1371/journal.pone.0068719
Putnam FW, 1872. The blind fishes of the Mammoth Cave and their allies. American Naturalist v. 6 (no. 1): 6-30. Also published in:
Packard, Jr. and Putnam 1872. Life in the Mammoth Cave, etc. chapter 3, pp. 29-54.

wiki/Spring_cavefish
wiki/Electrophorus
wiki/Lophius

The tarpon (Megalops): closer to piranhas than to eels in the LRT

…Well, at least it is not related
to the two tested eels in the LRT, the moray eel (Gymnothorax) and the European eel (Anguilla), which we looked at earlier here and here. The former is closer to lobe finned rhizodontids from the Devonian and Carboniferous. The latter is closer to barracuda. Are there other eels out there the tarpon might be closely related to? I’ll find out as I add taxa, I suppose.

Figure 1. Tarpon (Megalops) skeleton. Not very eel-like. Closer to the piranha.

Traditionally
the tarpon (Megalops atlanticus) has been considered an eel relative. Perhaps this is based on its life cycle, which includes elongated larvae born at sea. According to the Tennesee Aquarium, hatchling piranhas are also born tiny and slender.

Figure 2. Tarpon (Megalops) skull with tetrapod skull colors added. Note the large plate like postorbital and jugal here. Compare to Figure 3.

After testing
in the large reptile tree (LRT, 1511 taxa) Megalops (Figs. 1,2) nested with the piranha, Serrasalmus (Fig. 3). The former has hundreds of the tiniest teeth lining its jaws. The latter has a few large triangular teeth.

Figure 4. Piranha (Serrasalmus) skull.

Megalops atlanticus (Cuvier and Valenciennes 1847; up to 2.5m) is the extant Atlantic tarpon. Fast-swimming Megalops has large eyes and large fins. This open-seas predator sometimes uses its swim bladder as a lung by gulping air.

Figure 3. Subset of the LRT focusing on fish and updated here.

References
Cuvier G and Valenciennes A 1847. Histoire naturelle des poissons. Tome dix-neuvième. Suite du livre dix-neuvième. Brochets ou Lucioïdes. Livre vingtième. De quelques familles de Malacoptérygiens, intermédiaires entre les Brochets et les Clupes. 19: i-xix + 1-544 + 6 pp. Pls. 554-590.

wiki/Piranha
wiki/Serrasalmus
wiki/Tarpon

 

The giant oarfish (Regalecus) is a kind of seahorse!

The giant oarfish
(Regalecus glesne, Ascanius 1772; Figs. 1, 2) can be one of the longest bony fish in the sea, with the record holder measuring 11 meters. More commonly 3m is a typical length.

Until a closer sister taxon is added
to the large reptile tree (LRT, 1512 taxa) the giant oarfish nests with the seahorse (Hippocampus, Fig. 3). The oarfish can undulate its entire tail, like most fish. It can also undulate just the dorsal fin while the body itself remains essentially straight and motionless, much like a seahorse. The skin of is scaleless, but covered with tubercles (like sticklebacks and seahorses). The oarfish has been seen swimming vertically, tail down, like a seahorse. The short pectoral fins are vestiges. The long pelvic fins with oar-like tips are not used for locomotion, but trail behind.

Traditional cladograms
nest seahorses within the clade Percomorpha (perches, pufferfish, anglerfish, tunas, cichlids, etc.) distinct from the the clade Lampriformes (opahs, oarfish, etc.).

At present
the clade Percomorpha (Perca at its base) is confirmed, within the LRT (subset Fig. 4).

The clade Lampriformes is not confirmed as monophyletic.
Opah nests with flounders. Oarfish nest with seahorses.

Figure 1. The giant oarfish, Regalecus glesne, to scale with a couple of swimmers. Sometimes it swims vertically, often at great depths.

The skull is strange
and hard to score (Fig. 2). It is best understood like a seahorse with a short, bulldog-like rostrum, distinct from most long rostrum pipefish and sea horses.

Figure 2. Skull of the giant oarfish, Regalecus glesne. Note the mouth opens like a drawbridge with a dorsal premaxilla. The pectoral and pelvic girdles are merged. The elaborate postparietals anchor the cranial frill. Not sure about the ‘second quadrate’. I could find no homolog for that bone.

Let’s start with the fact
that the mouth is vertical and the premaxilla is dorsal, distinct from most vertebrates, except seahorses. The pectoral girdle is fused to the pelvic girdle. So the giant oarfish is nearly all tail.

Figure 3. The vertically rotated mouth found in the giant oarfish (Figs. 1, 2) is shared by the pipefish and seahorse clade shown here. Without these guides, the skull of Regalecus would be very difficult to figure out.

The eggs are 2.5mm in diameter.
Diet includes krill, small fish and squid, when large enough to prey on those items.

Other common names for the giant oarfish include:
Pacific oarfish, king of herrings, ribbonfish, and streamer fish.

Figure 4. Subset of the LRT focusing on fish/basal vertebrates.

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References
Ascanius P 1772. Philine quadripartita, et förut obekant sjö-kräk, aftecknadt och beskrifvet. Kongliga Vetenskaps Academiens Handlingar 33 (10-12): 329-331, pl. 10.,

https://www.dailymail.co.uk/news/article
wiki/Giant_oarfish

 

The European eel is a Bavarichthys sister

Updated January 16, 2021
with revised scores that now nest Xiphias, the swordfish, between Bavarichthys and Anguilla, the European eel. This is a novel hypothesis of interrelationships supported by skull shape and details, lack of ribs (in eels and swordfish) and a lack of pelvic fins in these two taxa. Traditionally these three taxa nest with other taxa. This clade is close to the anchovy clade in the LRT.

Updated December 17, 2020
with the addition of Fundulus to the LRT, Anableps moves away from Amia and Anguilla.

Earlier we looked at
the moray eel and the electric eel.

Today the European eel,
(Anguilla anguilla) enters the large reptile tree (LRT, 1510 taxa) alongside the barracuda, Sphyraena. Phylogenetically they are some distance away from the electric eel (Electrophorus) and the moray eel (Gymnothorax).

Figure 1. The European eel, Anguilla anguilla in vivo.

Figure 5. Skull of Anguilla, the European eel, compares well with that of Bavarichthys. Note the loss and reduction of preorbital bones.

Figure 6. Protanguilla is a recently discovered short eel, transitional from Bavarichthys in the LRT.

Anguilla anguilla (Linneaus 1758; up to 80cm in length, 1.5 exceptionally) is the extant European eel, a sister to the barracuda in the LRT. It lacks pelvic fins and the tail has reverted to a straight tail. The life cycle includes breeding and young hatching in the mid-Atlantic with migration back to European rivers before the adults return to the mid-Atlantic. Anguilla lacks the circumorbital bones, traits shared with the Northern Pike, Esox. Bones are relabeled here based on sister taxa.

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References
Gregory WK 1933. Fish skulls. A study of the evolution of natural mechanisms. The American Philosophical Society 23(2). Reprinted 1959, Eric Lundberg, Laurel FL, Noble offset printers, Inc. New York
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

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