Spinosaurus: Hone and Holtz 2021 minimize the unique traits

Summary for those in a hurry:
A unique morphology + a unique niche + a unique prey assemblage = a unique hunting technique.

From the Hone and Holtz 2021 abstract:
“We conclude that …the pursuit predation hypothesis for Spinosaurus as a “highly specialized aquatic predator” is not supported. In contrast, a ‘wading’ model for an animal that predominantly fished from shorelines or within shallow waters is not contradicted by any line of evidence and is well supported. Spinosaurus almost certainly fed primarily from the water and may have swum, but there is no evidence that it was a specialised aquatic pursuit predator.”

Hone and Holtz pay little attention to the fact that Spinosaurus was the only large theropod that had such short hind limbs and had a dorsal fin much deeper than its ribcage. The authors cherry-picked less obvious traits to support their hypothesis, giving only passing notice to what makes Spinosaurus unique.

From the Hone and Holtz introduction:
“In short, these animals [spinosaurs] acted like large herons or storks, taking fish and other aquatic prey from the edges of water or in shallow water, but also foraging for terrestrial prey and scavenging on occasion.”

In paleontology, if Spinosaurus is going to be compared to large herons or storks, it should look overall like a giant heron or stork. It does not.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Hone and Holtz keep hammering away at a single point:
“The hind limbs of Spinosaurus do potentially provide evidence for aquatic locomotion and even striking at prey underwater, but specifically not in the sense of pursuit predation.” 

“Surface swimming is considerably less efficient than submerged swimming and incurs considerable extra wave drag for animals moving at, or just below, the surface.”

The problem is, Hone and Holtz want Spinosaurus to be built for speed, like a sailfish, if they are to grant it a submerged aquatic existence. Unfortunately, the authors are caught in a logic rut based on some sort of straw man. They end up cherry-picking traits less important traits while trying to weave their story away from the larger, unique traits.

Spinosaurus was not built for speed.
It didn’t need to be built for speed. Look at the prey taxa available (Fig. 1). Lungfish, giant bichirs and coelacanths are big, fat and slow-moving fish. Sawfish are lethargic bottom-dwellers. Drag is not a factor when moving slowly, like Spinosaurus.

As the only aquatic dinosaur,
Spinosaurus may have developed a sail to help regulate body temperature while staying submerged (except to lay eggs). It may have never needed to stand bipedally, like its theropod sisters. Hence the small legs and quadrupedal center-of-balance.

The tiny backset naris of Spinosaurus
was on its way to complete closure. That’s not a problem as many extant birds without nares demonstrate. They can all breathe throughout their mouth and throat.

Figure 2. Diagram from Dal Sasso et al. 2005, colors and overlay added to show dorsal expansion of the maxilla to cover an elongate naris.

Hone and Holtz summarize their study:
“If swimming to engage prey, based on the drag, performance and body shape it would be limited to lunging attack in shallow waters, not pursuit predation at speed in open water.”

No.  Spinosaurus was a slow swimmer, unaffected by drag. It would not be limited to lunging attacks in shallow water, contra Hone and Holtz. Rather, slow, steady underwater predation with its sail exposed to maintain a 99º body temperature in an 80º river is still the best explanation for this unique theropod.

“The information provided through recent discoveries may suggest an increase in aquatic affinities for Spinosaurus, and it may have been able to swim with its tail, and even swim well compared to other theropods, but nothing presented to date contradicts the fundamentals of the ‘wading model’ and does not support active pursuit predation.”

Hone and Holtz failed to consider a semi-active, semi-submerged method of predation. “Nothing presented to date” = failure to consider all options. Spinosaurus is indeed a “highly specialized aquatic predator”, just not a fast one.

Earlier we looked at Spinosaurus in its environment here, its ability to swim deep here and its tiny naris here.

Unfortunately, papers from co-author David Hone are infamous for taxon exclusion, inaccurate observation, and illogical interpretation. Not sure why referees and editors are letting him get away with negating good solid science with bad flimsy science.

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References
Hone DWE and Holtz TR Jr 2021. Evaluating the ecology of Spinosaurus: Shoreline generalist or aquatic pursuit specialist. Palaeontologica Electronica 24(1):a03 Online Here.  

https://doi.org/10.26879/1110

Revisiting an Early Devonian bony fish: Doliodus

Over the past few weeks
I’ve been revisiting the 82 taxa currently in the ray-fin fish clade. Many were entered into the large reptile tree (LRT, 1793+ taxa) while I was still a ‘freshman’ in fish morphology. So it is no surprise that corrections are past due.

As an example,
earlier the nesting of swordfish with European eels and Bavaricthys was only a preview of what was to come. The work is never done.

Longtime readers know
making additions and corrections has been an ongoing process for the last ten years of this online study. The number of corrections made during that time is deep into six figures.

Today let’s revisit 
Doliodus problematicus (Whiteaves 1881; Traquair 1893; Miller, Cloutier and Turner 2003; Maisey et al. 2018; Early Devonian) a crushed skull with strange double-pronged teeth (Fig. 1). It was recently considered the ‘oldest articulated chondrichthyan’ and a transitional taxon between acanthodians and sharks. That is not confirmed in the LRT.

Figure 1. Doliodus from Maisey et al. 2018. Colors added. Compared to Malacosteus in figure 2.

Now
Doliodus nests with the extant, deep-sea, big-mouth, basal bony fish. Malacosteus (Fig. 2) in the LRT (Fig. x). The skull of Doliodus is wider, the maxilla is flat and the dual-pronged teeth are oriented medially (shown ventrally here, Fig. 1, for clarity). Considering this relationship, Doliodus might have been a nocturnal or deep-sea feeder. Convergent with spiny sharks, the leading edge of the Doliodus pectoral fin was a robust spine.

Figure 2. Malacosteus µCT scan from Kenaley 2007. Colors added. Compare to Doliodus in figure 1.

The stoplight loosejaw, a type of deep sea dragonfish,
Malacosteus niger (Ayres 1848, 1849; Kenaley 2007; 25cm; Fig. 2) is now a sister to Dolidodus in the LRT.  The eyeball is at the extreme anterior of the skull. The rostrum is minimized. The jaw joint is far behind. No operculum is present. The posterior dorsal and anal fins are much larger than the caudal fin. Light emitting organs are present posterior to the eye.

Figure x. Figure x. Current subset of the LRT focusing on ray-fin fish.

According to Kenaley 2007, 
“This genus is diagnosed within the Stomiidae by having enormous jaws, a single circular nostril on each side of the snout, a large tear-shaped accessory orbital photophore, serial photophores reduced in size and number, and intramandibular membrane, hyoid barbel, and palatine teeth absent.”

Kenaley 2007 does not mention Doliodus. Maisey et al. 2018 do not mention Malacosteus. So this (Fig. x) may be a novel hypothesis of interrelationships. If not, please provide a prior citation so I can promote it.

Figure 3. Malacosteus niger in lateral view.

Taxon inclusion and comparative anatomy
are the keys to understanding vertebrate interrelationships.

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References
Ayres WO 1848. pp. 64–73. In: Proceedings of the Boston Society of Natural History, Vol. 3. Proceedings of the Boston Society of Natural History, Boston.
Ayres WO 1849. Description of a new genus of fishes, Malacosteus. Boston Journal of Natural History 6:53–64.
Kenaley CP 2007. Revision of the Stoplight Loosejaw Genus Malacosteus (Teleostei: Stomiidae: Malacosteinae), with Description of a New Species from the Temperate Southern Hemisphere and Indian Ocean. Copeia. 2007 (4): 886–900. doi:10.1643/0045-8511(2007)7[886:
Maisey JG et al. (6 co-authors) 2018. Doliodus and Pucapampellids: Contrasting perspectives on stem chondrichthyan morphology. Chapter 5 in Evolution and Development of Fishes.
Miller RF, Cloutier R and Turner S 2003. The oldest articulated chondrichthyan from the Early Devonian period. Nature 435:501–504.
Traquair RH 1893. Notes on the Devonian fishes of Campbellton and Scaumenac Bay in Canada. No. 2. Geological Magazine, decade 3, 10: 145–149.
Turner S and Miller RF 2004. New ideas about old sharks. American Scientist 93:244–252.
Whiteaves JF. 1881. On some fossil fishes, Crustacea and Mollusca from the Devonian rocks at Campbellton, NB, with descriptions of five new species. Can Nat 10:93–101.

wiki/Malacosteus
wiki/Doliodus not yet published

 

A giant Eocene whale from Ukraine

Davydenko et al. 2021
report the discovery of new giant basilosaurid from Ukraine.

From the abstract:
“The earliest fully aquatic cetaceans arose during the Middle Eocene; however, the earliest stage of their divergence is obscure. Here, we provide a detailed redescription of an unusual early cetacean, “Platyosphys einori”, from the Late Eocene of Ukraine (37.8–35.8 million years ago), with new data on its body size, skeletal microanatomy and suggestions on phylogenetic relationships.”

By contrast, in the large reptile tree (LRT, 1793+ taxa) the earliest stage of ‘their divergence’ (mysticetes and odontocetes) extends back to tiny tree shrews in the Jurassic. Contra public and professional opinion, whale divergence is not obscure. Taxon exclusion hampers the Davydenko et al. study.

Figure 1. Cladogram from Davydenko et al. 2021 showing how they nested Playosphys einori. See figure 2 for their proposed mysticetes (with teeth!)

Unfortunately the authors presented an outdated cladogram
that considered the former clade ‘Cetacea’ monophyletic. Their paper perpetuates an invalid hypothesis of interrelationships (Figs. 1,2) that omits the ancestors of mysticetes: desmostylians, anthracubunids, hippos, mesonychids and oreodonts. They also omit the ancestors of pakicetids: tenrecs and anagalids.

Figure 2. Portion of the cladogram from figure 1 enlarged and rotated. Llancetus and kin are not mysticete ancestors when more taxa, like Behemotops, are included in the analysis.

Sadly,
whale workers continue to perpetuate the myth that whales are monophyletic. That was invalidated several years ago here by simply adding taxa.

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References
Davydenko S, Shevchenko T, Ryabokon T. et al. 2021. A Giant Eocene Whale from Ukraine Uncovers Early Cetacean Adaptations to the Fully Aquatic Life. Evol Biol (2021). https://doi.org/10.1007/s11692-020-09524-8

researchgate.net/publication/328388746_The_triple_origin_of_whales

reptileevolution.com/reptile-tree.htm

Wang et al. 2021: Vilevolodon had monotreme-like ear bones

We’ve heard this before.
Links below.

From the Wang et al. 2021 abstract:
“Recent discoveries of well-preserved Mesozoic mammals have provided glimpses into the transition from the dual (masticatory and auditory) to the single auditory function for the ossicles, which is now widely accepted to have occurred at least three times in mammal evolution.”

Wang et al. are not working from a valid phylogenetic context. They are not considering the possibility, hypothesized in the large reptile tree (LRT, 1593+ taxa) of a phylogenetic reversal in which the inner ear bones, which recapitulate phylogeny during embryonic ontogeny in placentals, could have stopped developing and stopped migrating to the typical placental position posterior to the mandible.

“Here we report a skull and postcranium that we refer to the haramiyidan Vilevolodon diplomylos (dating to the Middle Jurassic epoch (160 million years ago)) and that shows excellent preservation of the malleus, incus and ectotympanic (which supports the tympanic membrane).

See figure 1. We covered this issue earlier here, here and here.

Figure 1. Basal mammals and Vilevolodon as figured by Meng et al. Note in the other taxa the two jaw joints are nearly coincident. Not so in Vilevolodon.

From the Wang et al. abstract (continued)
“After comparing this fossil with other Mesozoic and extant mammals, we propose that the overlapping incudomallear articulation found in this and other Mesozoic fossils, in extant monotremes and in early ontogeny in extant marsupials and placentals is a morphology that evolved in several groups of mammals in the transition from the dual to the single function for the ossicles.”

Unfortunately
Wang et al. are pinning all their phylogenetic hopes on the inner ear bones. Therefore they are  “Pulling a Larry Martin.” Don’t do that. When placed into a phylogenetic analysis that considers traits from the entire skeleton and a wide gamut of mammals and pre-mammals, Vilevolodon nests within the placental clade Glires (the gnawers = rodents, rabbits, shrews, aye-ayes, multituberculates, etc.) We’ve known this for several years.

Wang et al. 2021 provide four prior analyses
in their SuppData, (references below) all of which employ suprageneric taxa, none of which test pertinent members of Glires.

In summary:
When tested against more taxa Vilevolodon is recovered as a derived member of Glires (rodents, rabbits, shrews, etc.) sharing with other multituberculates a neotonous retention of the embryonic condition, prior to the migration of the inner ear bones to the base of the skull, posterior to the mandibles. Evidently in their typical adult placental position typical ear bones interfered with the long slide of the mandible during gnawing and mastication, so retained the embryonic condition. The authors noted this ‘transition” in placentals in their abstract, but did not consider the possibility of a reversal or neotony.

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References
Han G, Mao F, Bi S., Wang Y and Meng JA2017. Jurassic gliding euharamiyidan mammal with an ear of five auditory bones. Nature 551, 451–456.
Luo Z.-X. et al. 2017. New evidence for mammaliaform ear evolution and feeding adaptation in a Jurassic ecosystem. Nature 548, 326–329.
Wang H, Meng J and Wang Y 2019. Cretaceous fossil reveals a new pattern in mammalian middle ear evolution. Nature 576, 102–105.
Wang J, Wible JR, Guo B. et al. 2021. A monotreme-like auditory apparatus in a Middle Jurassic haramiyidan. Nature. https://doi.org/10.1038/s41586-020-03137-z

Molnar et al. 2021: Forelimb function across the fish–tetrapod transition

Molnar et al. 2021
bring us a deep and complex look into the hypothetical muscles (based on muscle scars) of Eusthenopteron (Fig. 1), Acanthostega (Fig. 1) and Pederpes. The authors compare these distinctly different taxa to “show that early tetrapods share a suite of characters including restricted mobility in hurmerus long-axis rotation, increased muscular leverage of humeral retraction, but not depression/adduction, and increased mobility in elbow flexion-extension.” The authors infer the earliest ‘steps’ in tetrapod forelimb evolution were related to limb-substrate interactions. Weight support appeared later.

Figure 1. The fin to finger transition in the LRT with the addition of Elpistostege.

Unfortunately, 
without a valid phylogenetic context, what these authors deliver is not quite germane to the topic of their headline. The actual fin-to-finger transition occurred between Panderichthys (Figs. 1, 2) and the extremely similar Trypanognathus (Figs. 1, 2). The former had fins. The latter had fingers and toes. Otherwise they were very much alike.

Molnar et al. looked at the wrong taxa. Neither Panderichthys nor Trypanognathus are mentioned in the Molnar et al. text.

What can we conclude given
the similarities and differences of Panderichthys and Trypanognathus?

1. Small fins and limbs at the transition were incapable of weight bearing
2. Elbows and knees were incapable of bending, pushing, pulling
3. Torso much longer than tail, lots of flexible ribs
4. Low, wide, flexible torso at the transition provided serpentine locomotion
5. Little risk of tipping over due to low center of gravity

Figure 2. Dorsal and ventral views of Panderichthys and several basal tetrapods demonstrating the low, flat skulls and bodies with small limbs and relatively straight ribs.

Molnar et al. conclude:
“Together, these results suggest that competing selective pressures for aquatic and terrestrial environments produced a unique, ancestral “early tetrapod” forelimb locomotor mode unlike that of any extant animal.”

Not really. Consider the moray eel chasing crabs on land without fins or fingers. Click the pic to view video on YouTube. David Attenborough is the narrator.

Now put predator and prey in a Devonian swamp setting,
with lots of growing and rotting vegetation and no rocky place to find safety. Note (in figure 2), the rather slow phylogenetic growth of the limbs relative to the torso in this sequence. Other lineages did their own thing in their own time. Ossinodus, for instance (Fig. 1), had a shorter torso and longer limbs, and was a phylogenetic ancestor to Ichthyostega and Acanthostega.

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References
Molnar JL, Hutchinson JR, Diogo R, Clack JA and Pierce SE. 2021. Evolution of forelimb musculoskeletal function across the fish-to-tetrapod transition. Science Advances 2021; 7: eabd7457 22 January 2021

Enigma pterosaur wing bone from Late Campanian Utah

Farke 2021
brings us a large ‘pterosaur limb bone’ (Fig. 1) from the Late Cretaceous of Utah. The author guessed the bone was an ulna, but could not determine which end was proximal.

Figure 1. Ulna RMA 22574 from Farke 2021. Distal is at bottom.

From the abstract
“A large pterosaur bone from the Kaiparowits Formation (late Campanian, ~76–74 Ma) of southern Utah, USA, is tentatively identified as an ulna, although its phylogenetic placement cannot be precisely constrained beyond Pterosauria. The element measures over 36 cm in preserved maximum length, indicating a comparatively large individual with an estimated wingspan between 4.3 and 5.9 m, the largest pterosaur yet reported from the Kaiparowits Formation.”

That tentative identity as an ulna is confirmed here.  
Other than its more robust width and overall size, the bone is a good match for the ulna in the more completely known Triebold specimen of Pteranodon, NMC41-358 (Fig. 3). The overall size and relative length vs. width of RMA 22574 identifies this as a large Pteranodon (Fig. 2), perhaps the largest by a few percent, rather than a small azhdarchid (Fig. 4).

So, contra Farke 2021,
this specimen can be precisely constrained rather precisely beyond Pterosauria. It just takes a little comparative anatomy and taxon inclusion. Farke employed only one Pteranodon specimen (FHSM 184) for comparison, perhaps not realizing that no two known taxa are identical, even in the post-crania (Fig. 2), and others demonstrate a wide variation in size and morphology. By the way, FHSM 184 is a large solitary metacarpal 4.

Figure 2. The largest Pteranodon post-crania compared to RMA 22574, slightly larger than the largest.

A little repair work
to the broken proximal end (elbow) helps complete the match between RMA 22574 and NMC41-358 (Fig. 3).

Figure 3. Comparing RMA 22574 with the smaller and more gracile NMC41-358 scaled to the same length.

A selection of Pteranodon post-crania
can be seen to scale here and one of the largest is shown here (Fig. 2). Note the relatively shorter, broader antebrachia (= radius + ulna) in the largest, latest Pteranodon species relative to the humerus (Fig. 2 upper right). The relatively shorter, more robust, largest antebrachium with the characters of RMA 22574 is restricted to large, late Pteranodon specimens.

Figure 4. RMA 22754 compared to Quetzalcoatlus sp. which has a more slender radius.

Comparisons to appropriately sized azhdarchids
(Fig. 4) do not match as well. These tend to have a more gracile, hourglass appearance.

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References
Farke AA 2021. A large pterosaur limb bone from the Kaiparowits Formation (late Campanian) of Grand Staircase-Escalante National Monument, Utah, USA. PeerJ 9:e10766 https://doi.org/10.7717/peerj.10766

reptileevolution.com/pteranodon-skulls.htm
reptileevolution.com/pteranodon-postcrania.htm

Degrange 2021 revises Phorusrhacidae

From the Degrange 2021 abstract
“Phorusrhacidae, popularly known as ‘terror birds’, are the most speciose clade within the avian order Cariamiformes, with a fossil record that ranges from the Eocene to the Pleistocene. Although several species have preserved skulls, our understanding of their cranial morphology remains incomplete. Here, a comprehensive overview of the current knowledge of phorusrhacid skull anatomy is presented.”

Some phylogenetic issues here due to taxon exclusion.

Figure 1. Cariama and Sagittarius. The former is a sister to flamingoes. The latter is a sister to the terror birds in the LRT.

Unfortunately,
Degrange 2021 nests terror birds within the clade Cariamiformes, which include Cariama (Fig. 1) , the sister to Phoenicopterus, the flamingo in the large reptile tree (LRT, 1793+ taxa). By adding taxa, rather than relying on outdated tradition, Degrange should have nested phorusrhacids withe the secretary bird, Sagittarius (Fig. 1), the sister to phorusrhachids in the LRT. We looked at this taxonomic problem in September 2017. and again in November 2017.

Figure 2. Phorushacids to scale. The extant Sagittarius is in color at lower right.

According to Wikipedia,
“Molecular phylogenetic studies have shown that Cariamiformes is basal to the Falconiformes, Psittaciformes and Passeriformes” 

In the LRT Cariama and Sagittarius are basal to nearly all non-ratite birds. The above list omits galliformes (Gallus), which nest between falconiformes (Falco) and passeriformes (Passer) in the LRT.

Figure 3. Phorusrhacos to scale with Dinornis, Struthio and Homo.

Once again,
adding taxa while avoiding molecular studies and outdated traditions recovers a cladogram in which gradual evolution is demonstrated at every node.

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References
Degrange FJ 2021. A Revision of Skull Morphology In Phorusrhacidae (Aves, Cariamiformes) Journal of Vertebrate Paleontology Article: e1848855
DOI: 10.1080/02724634.2020.1848855

https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1848855

 

Xiphactinus has living relatives in the Amazon

Short one today
because all the work is not yet done with regard to ray fin fish phylogeny. This is just an update.

Previously I overlooked this novel hypothesis of interrelationships.
Now it seems obvious (Fig. 1). But first I had to better understand the crushed skulls of Xiphactinus (Figs. 1, 3) and Portheus (a traditionally junior synonym for Xipactinus, here resurrected due to several differences in the skull and post-crania, Figs. 2,4). Lots of little nips and tucks here.

Figure 1. Revised skull of Xiphactinus.

Figure 2. Revised skull of Portheus.

Figure 3. Xiphactinus fossil. The famous fish-within-a-fish. Note the posterior pelvic fins.

Figure 4. Skeleton of Portheus, close to but distinct from Xiphactinus. 

Figure 5. The araimaia, Hopolerythrinus, nests with the Cretaceous giants, Xiphactinus and Portheus (Figs. 1–4).

Figure 6. Araimaia (Hoplerythrinus) skull.

At present these three taxa
share a last common ancestor with an ancestor to Serrasalmus, the piranha.

Figure 7. Subset of the LRT focusing on ray fin fish. Eel-like taxa are highlighted.

Tyson’s Advice for Students

Production note: 
correction to the subtitles on the video: “Resighted” = “Recited” (spelling error)

Meanwhile
lots of earlier mistakes getting caught in the ray fin fish clade which continues to be under scrutiny (e.g. see yesterday’s post on swordfish). Hope to have all wrinkles ironed out soon. Thank you for your patience. The LRT is an ongoing hypothesis of interrelations subject to change with more data and more understanding.

And a Bonus Video from Joe Rogan featuring Avi Loeb

 

Correction: European eels are neotonous swordfish

Before you say, “That’s crazy!” did you ever notice
that swordfish lack ribs and pelvic fins (Fig. 4)? So do European eels.

More importantly, did you ever notice
that baby swordfish look like eels (Fig. 4)? Okay. With that in mind, let’s start with a little backstory and cover all the bases.

Traditionally swordfish have been allied with 
barracuda, marlin and several extinct billfish, including Blochideae (i.e. Blochius, Fig. 4), based on overall appearance, open sea niche and apex predator status. According to Wikipedia, “They [swordfish] are the sole member of their family, Xiphiidae.” Gregory and Conrad  1937 compared the morphologies of the sailfish and swordfish. Earlier I followed the lead of these experts in nesting the sailfish, Istiophorus (Figs. 5, 7), and the swordfish, Xiphiias, with the barracuda, Sphyraena. That was a mistake.

Today we’ll compare
swordfish and sailfish morphology to two other more closely related taxa: the anchovy, Elops (Fig. 6) and the European eel, Anguilla, which turns out to be more closely related to swordfish despite their outward differences as adults. Turns out that swordfish go through a metamorphosis as they develop from eel-like hatchlings with teeth (Fig. 4).

The LRT scores skeletal traits 
rather than superficial morphologies, which are always prone to reversal and convergence. The large reptile tree (1793+ taxa) is designed to test taxa together that have not been tested together before. Some surprises were recovered earlier using this method here, here and here.

In their description of Bavarichthys
(Fig. 1) Arratia and Tischlinger 2010 did not mention or test the eel, Anguilla, or the swordfish, Xiphias. Turns out, they should have done so.

Recent revisions
of several fish taxa (now that I have 250 fish taxa and the experience that brings to bear) reveal a hitherto overlooked hypothesis of interrelationships between eels and swordfish. Sound crazy? Keep reading. This is one of those ‘moment of discovery’ moments I want to share with you.

Figure 1. Bavarichthys is a big head/ short body anchovy from the Late Jurassic. Now it is ancestral to European eels.

Let the cheek plates evolve away in Bavarichthys
(Fig. 1) and you’l have the basic skull of both swordfish (Fig. 2) and European eels (Fig. 3). Note the triangular profile, the slender insertion of the nasal between the anterior frontals, the extreme brevity of the post-orbital portion of the skull, including a vertical quadrate. No other tested fish taxa have these traits.

Figure 2. Diagram of the swordfish (Xiphias) skull. Compare to figures 1 and 3.

Billfish came first. 
The European eel, Anguilla, is derived from swordfish, sailfish and Late Jurassic Bavarichthys. Hatchlings of swordfish are eel-like (Fig. 4) and Bavarichthys-like (Fig. 1). That means European eels are neotonous swordfish. They achieve adulthood while still in the hatchling swordfish stage. European eels also develop traits not found in swordfish, like additional vertebrae and a long, low operculum. European eels don’t develop pelvic fins of dorsal ribs. Neither do swordfish.

Figure 3. Skull of Anguilla, the European eel, compares well with that of Bavarichthys. Note the loss and reduction of preorbital bones.

Earlier the LRT nested
Late Jurassic Bavarichthys with closely related anchovies (genus: Elops), then with more closely related European eels (genus: Anguilla). Now it nests basal to both swordfish and European eels.

Other eels,
like the moray eel (Gymnothorax) and electric eel (Electrophorus) nest elsewhere, both near the base of the bony fish. So eels were in the gene pool.

Figure 4. Swordfish ontogeny (growth series). Hatchings have teeth, a short bill and an eel-like body still lacing pelvic fins. Hatchlings go through an eel-like phase and a sailfish-like phase.

Xiphias gladius
(Linneaus 1758; Gregory and Conrad 1937; up to 4.5m in length) is the extant swordfish, nesting between Bavarichthys and Anguilla. 1cm long hatchlings more closely resembled little eels, then growing to 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 and ribs are absent, as in eels. Larger females produce more eggs, up to 29 million.

Figure 5. Skull of the sailfish, Istiophorus. Compare to Elops in figure 6.

Figure 6. Elops is the extant anchovy. Compare to Bavaricthys in figure 1 and Istiophorus in figure 5.

Figure 7. Istiophorus, the sailfish, nests with the anchovy, Elops, not with, but close to the sailfish, Xiphias.

Sailfish have long slender pelvic fins,
like those of anchovies, unlike swordfish and eels. Sailfish have a broad postorbital, like anchovies, unlike swordfish. Sailfish have a zig-zag frontal-nasal suture, like anchovies, unlike swordfish. The list of subtle, but scoreable differences continues. More importantly, no other tested taxa share more traits with swordfish and sailfish than eels and anchovies, respectively.

Figure 8. Subset of the LRT focusing on ray fin fish. Eel-like taxa are highlighted.

With the sailfish and swordfish gone, where does that leave the lonely barracuda?
In the LRT the barracuda nests with the similar long-bodied remora (Remora) and cobia (Rachycentron), derived from the mahi-mahi (Coryphaena) all with mandibular prognathism. This is non-tradional. Other workers prefer to nest billfish with barracuda.

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References
Arratia G and Tischlinger H 2010. The first record of Late Jurassic crossognathiform fishes from Europe and their phylogenetic importance for teleostean phylogeny. Mitteilungen aus dem Museum für Naturkunde in Berlin. Fossil Record; Berlin 13(2): 317–341.
Gregory WK and Conrad GM 1937. The comparative anatomy of the swordfish (Xiphias) and the sailfish (Istiophorus). The American Museum Novitates, 952:1-25.
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.

https://pterosaurheresies.wordpress.com/2020/07/04/bavarichthys-a-late-jurassic-solnhofen-anchovy/

wiki/Istiophoriformes

wiki/Swordfish