Meiacanthus, a little venomous Western Pacific blenny enters the LRT with the much larger North Atlantic wolffish, also with dentary fangs

Meiacanthus grammistes
(originally Blennechis grammistes Cuvier and Valenciennes 1836, Fig 1) is the striped poison-fang blenny. It lives in the warm Western Pacific and grows to 11cm in length. The lower jaw is notable for its large venomous upside-down saber teeth.

Figure 1. Meiacanthus grammistes, the fang blenny, in several views from the venomdoc.com. Colors added here. Note the packed needle medial premaxillary teeth framed by larger premaxillary fangs separated by a diastema for the large dentary fangs when the jaws are closed. Note the vestigial maxilla (greeen stripe).

According to Wikipedia,
“The venom consists of a neuropeptide also seen in cone snail venom, a lipase similar to the one used by certain species of scorpions and an opioid peptide. Blennies use it to stun predators. The venom reduces the blood pressure of the predator, relaxing its jaws so the blenny can escape.”

VenomDoc.com reports:
“Fang blennies are a particularly fascinating group to research as they have a venomous bite instead of venomous spines like other fish, such as stingrays. They deliver a venom that is quite different from that of venomous spined fish, in that is not pain inducing. This is because they are not using their venom to deter larger predators but rather in fights with similar sized fish for territory. Their opioid peptide rich venoms induce dizziness in their competitors, giving the fang blenny an athletic competitive edge. If their competitors are extremely dizzy and uncoordinated, this would also make them easy prey for a predator…. thus being permanently removed from the competition!”

When added to
the large reptile tree (LRT, 2192 taxa), Meiacanthus (Fig 1) nests with another blenny, the several times larger (1.5m) Anarhichas, the Atlantic wolfish (Figs 2, 3) on the other side of the planet, in cold polar waters. The wolffish is traditionally considered close to scorpionifish, but Wikipedia reports, “The Atlantic wolffish has retained the bodily form and general external characteristics of small blennies (Blennioidei).” That’s an phylogenetic conflict resolved by the LRT.

Figure 2. Skull of the wolffish, Anarhichas. Note the large dentary fangs and robust circumorbital ring as in Meiacanthus (figure 1). Here the cranium is uniqely pinched behind the orbits, similar to cynodont mammals. I can’t think of another tested fish in the LRT that does this.

Olson 2017 reported,
“Smith et al. (2016) found that of the roughly 2,500 known venomous fish species, only two genera deliver venom with their fangs, including the one-jawed eel (Monognathus), and the fang-tooth blenny (Meiacanthus).”

Gene studies by Olson 2017
nest Meiacanthus with Channa among tested taxa. That’s not too far off from the LRT results. Unfortunately, Olson also nests Anarhichas with Gasterosteus, the stickleback. That’s very far off from the LRT, which nests sticklebacks with pipefish and sea horses based on traits.

Figure 3. Anarhichas in vivo. At 1.5m, this is what happens to blennies that enter the Atliantic. This taxon is not venomous. Pelvic fins are lost.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.

References
Cuvier G and Valenciennes A 1836. Histoire naturelle des poissons. Tome onzième. Livre treizième. De la famille des Mugiloïdes. Livre quatorzième. De la famille des Gobioïdes. v. 11: i-xx + 1-506 + 2 pp., Pls. 307-343. [Valenciennes authored volume. i-xv + 1-373 in Strasbourg edition.]
Olson E 2017. The evolution of fangs across ray-finned fishes (Actinopterygii). Culminating Projects in Biology. 22.https://repository.stcloudstate.edu/biol_etds/22

wiki/Meiacanthus_grammistes
wiki/Atlantic_wolffish
http://www.venomdoc.com/
The Sidney Morning Herald: Meet the fang blenny

Anableps, the four-eyed fish, now nests with Periophthalmus, the mud skipper

Traditionally
Anableps, the four-eyed fish (Figs 1, 2), was considered a member of the Cyprinodontiformes (tooth carps, killifish, top minnows like Fundulus). At 32 cm in length, Anableps would be the largest of that clade.

Most recently
Anableps entered the large reptile tree (LRT, 2191 taxa, Fig 3) close to Lepidogalaxias, the salamanderfish. The large eyes, rounded fins and posterior position of the pelvic fin, a primitive trait, helped inform that decision. Turns out there was a closer match with taxa that had evolved pelvic fins closer to the skull. That means a reversal may have occurred.

Figure 1. Anableps in lateral view.

Here
with new identities applied to several skull bones (Fig 2) Anableps now nests with another surface fish with elevated orbits and able to breathe air, the mudskipper, Periophthalmus (Fig 3).

Figure 2. Anableps skull parts from Michel et al 2015 re-colored with tetrapod homologies. The original labels are sometimes incorrect. If you’re going to color individual bones, do not surround them with big black outlines. Keep it simple and clean.

Anableps tetrophthalmus
(originaly Cobitis anableps Linnaeus 1758, Scopolis 1777; Michel et al. 2015; 32 cm) is the extant four-eyed fish (aka: cuatro ojos), a surface predator of insects falling into Amazonian fresh waters or shallow shores where Anableps sometimes beach themselves to eat them. The underslung jaw enables this behavior. Internal fertilization (with a modified tubular anal fin) leads to live birth (viviparity) of up to 14 young.

Figure 3. The mudskipper, Periophthalmus, nests with the neon goby, Elacatinus, in the LRT.

Periophthalmus sp.
(Bloch and Scheider 1801) is the extant mudskipper, a goby often seen sunning itself above the surface of the water. The pelvic fins help grip the undersurface. Underwater, mudskippers stay close to the bottom.

Mudskippers and four-eyed fish are most closely related to frogfish
among tested taxa in the LRT. That’s the problem. Superficiifally mudskippers and four-eyed fish don’t look like frogfish, but dig down to their skelelton and their interrelationships are revealed. This phylogenetic reversal to a more plesiomorphic shape could be due to phylogenetic miniaturization, which includes neotony. The hatchlings of frogfish look more like long, small-skull primitive fish, then quickly enlarge the skull to adult frogfish proportions. This is an issue that needs further study for confirmation, refutation or modification.

Figure 4. Subset of the LRT focusing on derived ray fin fish, including Anableps.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.

Anableps has been a difficult taxon to confidently nest.
It has bounced around the LRT. Three earlier posts about Anableps have been deleted in order to reduce confusion. As mentioned earlier, hundreds of thousands of corrections have been made to the LRT and the data presented at ReptileEvolution.com. Corrections will continue to be made wherever warranted. Case in point: Anableps. If it moves again, I will be surprised.

Gobies and blennies are supposed to be closely related.
In the LRT they are not. Blennies are in the deep ancestry of gobies.

References
Bloch ME and Schneider JG 1801. M.E. Blochii, Systema Ichthyologiae iconibus cx illustratum. Post obitum auctoris opus inchoatum absolvit, correxit, interpolavit Jo. Gottlob Schneider, Saxo. Berolini. Sumtibus Austoris Impressum et Bibliopolio Sanderiano Commissum. Pp i-lx + 1-584, Pls. 1-110.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Michel KB, Aerts P, Gibb AC and Van Wassenberg S 2015. Functional morphology and kinematics of terrestrial feeding in the largescale foureyes (Anableps anableps). Journal of Experimental Biology (2015) 218, 2951-2960 doi:10.1242/jeb.124644

wiki/Periophthalmus
wiki/Four-eyed_fish_Anableps

Neilpeartia: an Eocene frogfish

Neilpeartia ceratoi
(Carnevale et a. 2020, Eocene) is the earliest known frogfish tested in the LRT. Even so, it greatly resembles the extant frogfish, Antennarius.

Figure 1. Neilpeartia in situ with color tracing and reconstruction based on that tracing (= DGS method).

Frogfish are related to deep sea anglers
like Himantolophus. These are related to flat, benthic anglers, like Lophius. Currently relatively plesiomorphic gobies like Elacatinus nest with these taxa, but that odd hypothesis appears to be an issue best resolved by more housekeeping and adding a few more taxa.

Figure 2. Frogfish ontogeny featuring Antennarius. The pelvic fins are highlighted in pink.

The answer to this issue may be staring us right in the face.
In figure 2 the hatchlings don’t have exaggerated frogfish triats. They look more plesiomorphic, like gobies. Then let us remember that gobies include some of the smallest of all fish (Fig 3).

Figure 3. The dwarf goby, Trimmatom nanus, shown at full scale @72dpi and enlarged to show details.

The dwarf goby,
Trimmatom nanus (Fig 3) is about a centimeter in length. Is this yet another case of phylogenetic miniaturization? It’s going to be tough to find a skull and skeleton for this one.

References
Carnevale G et al (5 co-authors) 2022. †Neilpeartia ceratoi gen. et sp. nov., a new frogfish from the Eocene of Bolca, Italy. Journal of Vertebrate Paleontology 40(2):e1778711.

wiki/NeilPeartia – not yet posted
wiki/Trimmatom nanus

Traditional bony fish evolved from spiny sharks in the LRT

Recent housekeeping
in the large reptile tree (LRT, 2189 taxa, Fig 2) now nests all the extant and extinct pachycormiformes (Figs 3, 4), with the Devonian spiny sharks (Fig 1, Acanthodii).

This is yet another example of why we should not list traits to determine clades. Rather we should use the last common ancestor method to determine clades (using traits, not genes). That means we writers and readers are also members of the monophyletic Acanthodii.

Figure 1. Ischnacanthus is a basal acanthodian in the LRT. It is closer to outgroup tiny placoderms than other spiny sharks. Here this taxon is shown 1.3x life size.

Spiny sharks (Acanthodii)
are not strange long lost oddities. They are ancestors of all bony fish and descendants of placoderms. Two early splinters (Fig 2, Osteoglossum and Notopterus, Fig 5) survive to this day.

As transitional taxa,
spiny sharks demonstrate transitional morphologies between placoderms and bony fish. The genesis of this transition is once again marked by phylogenetic miniaturization with Shenacanthus, about the size of an inch worm.

Figure 2. Subset of the LRT focusing on the spiny sharks (Acanthodii), their ancestors and descendants. Note the many times ray fins and coalesced spines evolve from this clade. All fish in the yellow box are part of the monophyletic clade Acanthodii.

According to Wikipedia,
“Pachycormiformes is an extinct order of marine ray-finned fish known from the Early Jurassic to the end of the Cretaceous.”

In the LRT two members of the ‘extinct’ Pachycormiformes remain extant.

Figure 3. Three traditional pachycormiformes nest within the grade Acanthodii. Note the variety of pectoral and pelvic fins in these closely related taxa.

According to Wikipedia,
“Pachycormiformes are generally interpreted as members of Teleosteomorpha, the group that includes all fish more closely related to modern teleosts than to Holostei (the group containing bowfin and gars), often they have been considered to be the sister group of the Aspidorhynchiformes.”

In the LRT Aspidorhynchus (Fig 3) is instead a clade member of the Pachycormiformes.

Contra Wikipedia, in the LRT, members of the traditional Holostei do not nest together, so that’s an invalid clade. BTW, in the LRT no taxa are ever ‘considered’. All taxa are tested.

Figure 4. The largest bony fish ever, Leedsichthys, and related taxa are all acanthodians (spiny sharks) in the LRT.

Earlier
the extant bronze featherback, Notopterus (Fig 5), nested with spiny sharks like Brochoadmones. Now these two are joined by pachycormiformes in the LRT (subset Fig 2). Osteoglossum, the extant arowana, also arises (splits off earlier on.

Figure 5. The first traditional bony fish to nest with acanthodians in the LRT is the extant bronze featherback, Notopterus.

A popular little spiny fish, the stickleback
(Gasteroseus), is not related to Devonian spiny sharks (Acanthodii), despite their many spiny fins. Spiny pelvic and dorsal spines reappear here perhaps due to a genetic reversal becayse acanthodiians are in the lineage of sticklebacks and tetrapods, like the stegosaur, Kentrosaurus.

Figure 6. The stickleback, Gasterosteus, experiences a reversal and reacquires dorsal and pelvic spines from ancient acanthodian ancestors.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it her.

References
wiki/Pachycormiformes
wiki/Acanthodii
wiki/Aspidorhynchiformes

Brochoadmones: a closer featherback (Notopterus) precursor

Another clade no longer extinct: Acanthodii (spiny sharks)

After analysis, Early Cretaceous Bishops is NOT the immediate sister to therian mammals

Flannery et all 2022 concluded,
“Bishopids fam. nov. are the immediate sister taxon to therian mammals.”

The LRT does not confirm this hypothesis of interrelationships.

By contrast, after analysis,
In the large reptile tree (LRT, 2188 taxa), Early Cretaceous Bishops (Fig 1) is a therian mammal close to the Late Cretaceous marsupial Asioryctes (long rostum specimen, Fig 2) and the extant bandicoot (Perameles, Fig 3). So Bishops is not the immediate sister to therian mammals (= marsupials + placentals), contra Flannery et al 2022. It is one of the therian mammals, nested deep inside. Longtime readers of the LRT have known this since 2018.

Unfortunately, Asioryctes is not mentioned in the Flannery et al 2022 text, which deals largely with dental traits. Teeth provide only a few characters in the LRT.

Figure 1. Early Cretaceous Bishops dentary and teeth to scale with its much smaller Late Cretaceous LRT sister, Asioryctes, shown about 0.9x life size.

From the Flannery et al 2022 abstract:
“A review of the Southern Hemisphere Mesozoic tribosphenic mammal fossil record supports the hypothesis that Tribosphenida arose in the Southern Hemisphere during the Early Jurassic, around 50 million years prior to the clade’s reliably dated first appearance in the Northern Hemisphere.

This confirms earlier recoveries by the large reptile tree (LRT, 2189 taxa) based on nesting both Late Jurassic multituberculates and Maiopatagium deep within the placental clade Glires.

“Mesozoic Southern Hemisphere tribosphenic mammals are known from Australia, Madagascar, South America and the Indian subcontinent, and are classified into three families: Bishopidae (fam. nov.), Ausktribosphenidae and Henosferidae. These are stem therians, and considerable morphological evolution occurred within the lineage between the Jurassic and late Early Cretaceous. Important dental modifications include a graduated transition between premolars and molars, development of molar wear facets V and VI, loss of facets for postdentary bones, reduction in the Meckelian groove and development of a true dentary angle. Previous classifications of Southern Hemisphere tribosphenic mammals are ambiguous because information from the upper dentition has been lacking. Upper molars attributed to the late Early Cretaceous (Albian) Southern Hemisphere group Bishopidae fam. nov. are now known to possess a prominent protocone and stylar cusp C. We thus consider bishopids to be the sister group to Theria.”

It’s great to discuss traits, but let’s always rely on the last common ancestor method. Run your analysis, then discuss traits as they apply to related taxa in your cladogram.

Figure 2. What little is known of Early Cretaceous Bishops compared to its Late Cretaceous sister, Asioryctes, which nests among the basal marsupiials, the bandicoots in the LRT. Note, the teeth are not the same, but everything else is similar, more similar than all the other competing mammals in the LRT.

According to Wikipedia,
“Tribosphenida is a group (infralegion) of mammals that includes the ancestor of Hypomylos, Aegialodontia and Theria (the last common ancestor of marsupials and placentals plus all of its descendants).”

Not sure why everyone, it seems, is trying to define new clades… unless they are relying on unreliable dental traits. This needs to stop. Use the last common ancestor method based on largely complete skeletons, not genes, not teeth.

Theria still works in the LRT. The other two newer clade names do not.

Figure 3. Skulls of Asioryctes, Perameles and Macrotis compared.

The key to repairing / improving Flannery et al 2022
is to add Bishops to an analysis that includes a wide gamut of taxa, including the long rostrum specimen of Asioryctes and the bandicoot, Peramelles (Fig 3).

References
Flannery TF et al (4 co-authors) 2022. The Gondwanan Origin of Tribosphenida (Mammalia). Alcheringa: An Australasian Journal of Palaeontology DOI: 10.1080/03115518.2022.2132288
Rich et al 2001. A second tribosphenic mammal from the Mesozoic of Australia. Records of the Queen Victoria Museum 110, 1–9.

Publicity
sciencealert.com/jawbone-discovery-suggests-modern-mammals-originated-in-the-southern-hemisphere

“The researchers suggest the specialized molars of our earliest mammalian ancestors might have been the key to their evolutionary success. But the evolution of early mammals who outlived the dinosaurs has long fascinated scientists and will no doubt continue to attract ongoing scrutiny.”

Let’s remember, dinosaurs are still living as birds. Is this nitpicking?
Or just trying to correct the narrative?

wiki/Tribosphenida
wiki/Theria
wiki/Asioryctes
wiki/Marmosa
wiki/Maelestes
wiki/Bishops

https://pterosaurheresies.wordpress.com/2018/09/23/bishops-enters-the-lrt/

Timeline of Tetrapod and Reptile Origins

The last common ancestor of all reptiles
so far tested in the large reptile tree (LRT, 2188 taxa, subset Fig 1) is Silvanerpeton (Fig 5). Because it nested at that node, we know it produced eggs with an amnion, a water tight membrane invented by a reptile close to Silvanerpeton and shared by all members of the monophyletic clade, Reptilia. Amniota is a junior synonym.

Silvanerpeton lived during the Viséan stage
of the Early Carboniferous. With so few specimens known, we don’t know how early this genus appeared on the planet, nor how long it survived beyond this period. We are lucky to have this rare genus.

Not shown here (Fig 1) are several derived reptiles, like Eldeceeon, that also lived during the Viséan. The presence of coeval reptiles indicate they had already radiated by that time. That means reptiles had an earlier genesis. How much earlier? The timeline can help.

Figure 1. Subset of the LRT focusing on the origin and ancestry of reptilles and a color chronology to show when fossils are known, not when taxa first appeared. Note how many taxa more primitive than Early Carboniferous Silvanerpeton are known from the Early Carboniferous and later, indicating a rapid radiation for all basal tetrapods.

Today’s topic explores
the proximal and more distant ancestors of reptiles, none of which provided an amnion to protect their embryos. We know this from phylogenetic bracketing, not from fossils.

The LRT provides the blueprint: the family tree.
A little research permitted the application of time colors (Fig 1) to the each of the ancestors of Silvanerpeton and their descendants. Some of these (e.g. lungfish and frogs) exist today.

This LRT timeline shows
all basal tetrapods evolved on a fast-track for their first 20 million years. This takes human ancestors from the transition of fins to fingers to the invention of the amnion.

Figure 2. Collosteidae include Collosteus, Pholidogaster, Greererpeton and Deltaherpeton all to scale.

This LRT timeline also documents
a second, parallel lineage of para-tetrapods, the Collosteidae (Fig 2). These fish-like taxa with fingers and toes, had an earlier phylogenetic origin than Tetrapoda. Unfortunately, colllosteid fossils are only known from the Carboniferous. Even so, they may have been the ones that left footprints during the Middle Devonian.

Figure 3. Acanthostega does not have much of a neck.

This LRT timeline also shows
the famous Late Devonian tetrapods, Acanthostega (Fig 3) and Ichthyostega, were not pioneers, but late survivors of an earlier radiation of basal tetrapods. These two polydactyls produced no descendants.

Instead, the most basal tested tetrapod in the LRT
is late surviving Late Carboniferous four-fingered Trypanognathus (Fig 4). It shares more traits with finned Panderichthys than any competing taxa. Thus, contra to what is taught in university textbooks, the most basal tetrapods had limbs too small to lift their belly off the muddy or sandy substrate, just like their panderichthyid ancestors. Unfortunately, this hypothesis remains heretical three years after its proposal.

Sadly paleontology takes decades to drop invalid traditions, as Yale professor John Ostrom lamented. On the other hand, paleontology embraces myths much more quickly. We still have the bat wing bird, for instance.

Figure 4. Vertebrates at the transition from stem-tetrapod to tetrapod in the LRT. Phylogenetically miniaturized Trypanognathus is the most primitive known tetrapod in the LRT, despite its late appearance in the fossil record of the latest Carboniferous.

As mentioned above, the earliest, but not the most primitive tetrapods
(Fig 3) are known from Late Devonian skeletons. Skipping all the transitional taxa, the LRT nests another Late Devonian taxon, Tulerpeton (Fig 5), as a proximal ancestor to Silvanerpeton. So that pushes the origin of reptiles back to the Late Devonian. That’s okay if the transition from fins to fingers shifts back to those Middle Devonian tetrapod tracks.

Figure 5. Tulerpeton restored based on the bauplan of Silvanerpeton and to the same scale.

Every taxon directly between Trypanognathus and Tulerpeton
(Fig 1) must have also had their origin and initial radiation during the Late Devonian. So look for those taxa in those strata. The LRT shows all other currently known reptilomorphs (Fig 1) are coeval to or later than basalmost reptile Silvanerpeton.

Phylogenetic analysis can extend our understanding
of the origin of fossil genera beyond their present chronology based on strata. Thus wide gamut cladograms, like the LRT (subset Fig 1), can have predictive value when combined with the element of time.

References
wiki/Colosteidae
wiki/Amniote
wiki/Reptile
wiki/Reptiliomorpha
wiki/Tetrapod
wiki/Phylogenetics

Kolponomos ,”the Miocene beach bear,” moves to the desmostylians in the LRT

Updated February 2, 2023
with new scores moving Kolponomos (Figs 1, 2) close to the desmostylian, Cornwallius (Fig 2).

Knee-high to a human,
early Miocene Kolponomos (Stirton 1960, Tedford, Barnes and Ray 1994, Fig 1) moves in the large reptile (LRT, 2189 taxa then, 2212 taxa now) between Paleoparadoxia and Cornwallius. The latter is from the same formation in Vancourver.

Figure 2. The pre-desmostylian Cornwallius. Here the tympanic bulla (bright green) was considered “a mass” in the text and otherwise was not labeled.

Traditionally
Kolponomus was considered a bear relative, “a beach bear” perhaps close to pinnipeds. A few postcranial bones are known indicating this taxon was amphibious, but not a strong swimmer.

According to Wikipedia,
“The discovery of more fossils including a nearly complete cranium (Fig 1) from the original locality of K. clallamensis which helped identify it as part of the group from which pinnipeds evolved.”

The LRT indicates this a matter of convergence with desmostylians.

“In life, species of Kolponomos had downturned snouts and broad, heavy molars that would have been suited to a diet of hard-shelled marine invertebrates, and their narrow snouts and anteriorly directed eyes indicate that they would have had stereoscopic vision. Large neck muscle attachments and robust foot bones combine with these features to suggest that Kolponomos filled a unique niche among marine carnivores, approached today only by the very distantly related sea otter.”

Essentially desmostylians, like Kolponomos, are marine hippos
transitional to baleen whales (Mysticeti). The crushing cheek teeth of Kolponomos are desmostylian in architecture.

Tseng, Grohé and Flynn 2016 reported,
“Mammalian molluscivores feed mainly by shell-crushing or suction-feeding. The extinct marine arctoid, Kolponomos, has been interpreted as an otter-like shell-crusher based on similar dentitions. However, neither the masticatory biomechanics of the shell-crushing adaptation nor the way Kolponomos may have captured hard-shelled prey have been tested. Based on mandibular symphyseal morphology shared by Kolponomos and sabre-toothed carnivores, we hypothesize a sabretooth-like mechanism for Kolponomos prey-capture, whereby the mandible functioned as an anchor. This unique feeding system of Kolponomos exemplifies a mosaic of form-function convergence relative to other Carnivora.”

Perhaps taxon exclusion is the problem with prior studies. Kolponomos has a shorter face than related desmostylians (Fig 2) which has led to an ursid, pinniped, carnivore hypothesis of interrelationships in prior reports (see reference list).

References
Stirton RA 1960. A Marine Carnivore from the Clallam Miocene Formation, Washington: Its Correlation with Nonmarine Faunas. University of California Publications in Geological Sciences. 36 (7).
Tedford RH, Barnes LG and Ray CE 1994. The early Miocene littoral ursoid carnivoran Kolponomos: Systematics and mode of life (PDF). Proceedings of the San Diego Society of Natural History. 29: 11–32.
Tseng ZJ, Grohé C and Flynn JJ 2016. A unique feeding strategy of the extinct marine mammal Kolponomos: convergence on sabretooths and sea otters. Proceedings of the Royal Society B: Biological Sciences 283(1826)     DOI: 10.1098/rspb.2016.0044

wiki/Kolponomos

Odd Carboniferous Harpacanthus updated

Updated January 2, 2023
with a new hypothesis of mouth bone identities.

Harpacanthus fimbriatus
(Traquair 1886; Lund and Grogan 2004; Carboniferous; Bear Gulch Fm 320mya) is traditionally considered a cartilaginous fish with a unique set of six rostral ‘claspers’ (Fig 1 upper image).

Like, but unlike iniopterygian pectoral fins.
Like, but unlike the Falcatus dorsal spine.
Like, but unlike the laterally extended labial cartilages of the ray-like Jagorina and Squatina
Like, but unlike the medial rostral rod of the ratfish Callorhinchus or Rhinochimaera.
Like, but unlike the four jointed toothy rostral ornaments of the male Harpagofututor.
Like, but unlike the anteriorly-placed, spine-like fins of Aquilolamna.
Like, but unlike the seven immobile branching nasal processes of Squaloraja.

Figure 1 upper image. Harpacanthus from Lund and Grogan 2004. Lower image is the earlier revision here updated in figure 2.

Instead of nesting with the odd chondrichthyans listed above,
Harpacanthus nests in the large reptile tree (LRT, 2188 taxa) with the equallly bizarre, but decidedly different, cave dwelling, sarcastic fringehead, Neoclinus (Figs 3, 4). Among the 421 tested fish and basal tetrapods, PAUP recovered these two as more like each other. This small phylogenetic shift from a close association with moray eels (Fig 5) occurred after re-scoring a fresh tracing of Harpacanthus (Fig 2) during the latest round of ‘housekeeping’ (= making corrections).

Figure 2. Harpacanthus in situ from Lund and Grogan 2004. Colors added here. Original tracing above. Novel reconstruction presented here based on similarities to Neoclinus (figure 3, 4).

Figure 2a. Harpacanthus in situ from Lund and Grogan 2004. Colors added here. Original tracing above. Novel reconstruction below. Here the amber bar without teeth is the circumorbital bar. Green is the maxilla. Yellow is the premaxilla. Note sure about those teeth. Compare to Neoclinus in figure 4.

The hypothesis that the six toothy elements
were gill bars with teeth, as in moray eels (Fig 5), continues today. Overall a better match was found in Neoclinus, which has toothy gill bars (Fig 3), but lacks the ability to move them. Sans the rest of the skeleton, in 1886 these curved toothy bars were the first loose parts of this taxon known leading to much speculation as to what sort of animal they belonged to until Lund and Grogan published in 2004.

Figure 3. The sarcastic fringehead becomes bizarre when opening its mouth in a threat gesture.

Lund and Grogan 2004 produced
a Harpacanthus diagram (Fig 1, upper image) that was modified here a few years ago (Fig 1, lower image). That first attempt included several errors rectified today (Fig 2). Corrections are a continuing process here and hopefully elsewhere, too.

Figure 4a. Skull of the sarcastic fringehead, Neoclnus, in two views, with the maxilla in its relaxed state. Colors added here.

Figure 4b. The sarcastic fringehead, Neoclinus, isolated on plastic.

Neoclinus is an underwater cave-dwelling fish
that does strange things with its maxillae (Figs 3, 4), but keeps its gill bars inside its throat. Gymnothorax, the moray eel (Fig 5), uses its movable toothy gill bars to help snatch prey and pull it back to the throat.

Figure 5. GIF animation showing the dual bite of the dual jaws in moray eels. The posterior set are derived from gill bars.

This new nesting also appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.

References
Lund R and Grogan E 2004. Five new euchondrocephalan Chondrichthyes from the Bear Gulch Limestone (Serpukhovian, Namurian E2b) of Montana, USA. In G. Arratia, M. Wilson, R. Cloutier (eds.), Recent Advances in the Origin and Early Radiation of Vertebrates 505-531.
Traquair RH 1886. On Harpacanthus, a new genus of Carboniferous Selachian Spines. Journal of Natural History. Series 5. 18(108): 493–496.

wiki/Sarcastic Fringehead
wiki/Harpacanthus

Kentrosaurus enters the LRT alongside Stegosaurus

No surprises here.
The skull of Kentrosaurus (Fig 1) is known from just a few disconnected pieces. The post-crania differs little from the more completely known, Stegosaurus, other than plate and spine patterns. As mentioned earlier, there are no more large gaps in the large reptile tree (LRT, 2188 taxa). Additional taxa are going to be pretty much like something already present and tested.

FIgure 1. Kentrosaurus in a bipedal pose from Gierlinski and Sabath 2008.

In support of bipedal abilities in stegosaurs, Gierlinski and Sabath 2008 reported,
“Isolated pedal ichnites from the Morrison Formation (with a single tentatively associated manus print, and another one from Poland) and the only known trackways with similar footprints (Upper Jurassic of Asturias, Spain) imply bipedal gait of their trackmakers. Thus, problems with stegosaur tracks possibly stem from the expectation of their quadrupedality. Massive but
short stegosaur forelimbs suggest primarily bipedal locomotion, and quadrupedal defense posture.”

According to Manospondylus.com, re: Stegosaurus:
“Marsh’s initial vision of the animal was a sort of turtle-like dinosaur that lived mostly in water, but when coming out on land would walk bipedally. The latter idea derives in part from the disproportionate length of the limbs (though mind you some of these came from an Allosaurus, as mentioned), but also because it was commonly thought between the 1860s and the 1870s that all dinosaurs were bipeds, as the most complete dinosaur skeletons up to that point were those of Hadrosaurus and Dryptosaurus (Laelaps).”

Kentrosaurus aethiopicus
(Henning, 1915, Late Jurassic 4.5m) is a smaller stegosaur with more spines, rather than plates, from East Africa. Note the robust, but short forelimbs here elevated in a bipedal pose, as originally proposed for Stegosaurus and later agreed to by Bakker 1986.

References
Bakker RT 1986. The Dinosaur Heresies. New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction, New York.
Gierliński GD and Sabath K 2008. Stegosaurian footprints from the Morrison Formation of Utah and their implications for interpreting other ornithischian tracks. Oryctos 8:29–46.
Hennig E 1915. Kentrosaurus aethiopicus, der Stegosauridae des Tendaguru. Sitzungsberichte der Gesselschaft natuforschender Freunde: 219-247. Berlin.

wiki/Stegosaurus
wiki/Kentrosaurus

manospondylus.com/2022/06/stegosaurus-history-of-reconstructions
manospondylus.com/2019/11/whatever-happened-to-kangaroo-kicking

New data on the skeleton of Ichthyornis, a Cretaceous sea bird

Benito et al 2022
added to our knowledge of the previously incomplete taxon, Ichthyornis (Fig 1). Now this toothed sea bird of the Niobrara is missing only a few toe bones (Fig 2).

Figure 1. From Benito et al 2022. Missing red toes added here. Pedal phalanx identity remain guesses.

Interestingly…
Ichthyornis documents gastralia AND a deep sternum, both apparently by convergence with more basal and more derived taxa respectively. The word ‘gastralia’ is not found in the Benito et al text.

Be careful…
with those pedal phalanges. Benito et al reported, “The pedal phalanges of Ichthyornis are described in detail for the first time (Fig. 29); although it is impossible to infer their position with certainty, precluding a complete reconstruction of foot anatomy for Ichthyornis, the proportions of these phalanges in comparison with the rest of hindlimb elements suggest a greatly enlarged pes, presumably adapted for foot-propelled swimming.”

Or a somewhat reduced metatarsus. The difference depends on your starting point. Here (Fig 2) the missing phalanges are estimated based on the closest known relative in the large reptile tree (LRT, 2186 taxa), Early Cretaceous Changzuiornis (Fig 3), which has a relatively longer metatarsus and more of a sand plover morphology overall.

The new data was entered into the LRT. The postion of Ichthyornis did not change.

Figure 2. The right pes of Changzuiornis (left) alongside the right pes of Ichthyornis (right). Missing phalanges are estimated here based on the more complete pes of the sister taxon.

Changzuiornis
(Fig 3) is not mentioned in Benito et al, Chanzuiornis also has gastralia. The sternum remains unknown, likely buried in the matrix. We need a µCT scan here to see below the rock surface.

Figure 3. Changzuiornis in situ, isolated from matrix, and repositioned to an invivo pose.

Ichthyornis dispar
(Marsh 1872) Late Cretaceous ~90 mya, 24 cm in length, wingspan 43 cm was a deep-breasted, tern-like flying bird derived from Apsaravis, Juehuaornis and Changzuiornis. Like outgroup taxa, the skull of Ichthyornis had a long rostrum with teeth largely missing from the anterior half of the upper rostrum. The premaxilla was extended to form a sharper tip. The naris was larger than the antorbital fenestra. The dorsal ribs were elongated and tied together with short uncinate processes.

Unfortunately, taxon exclusion mars the Benito et al cladogram,
which nests Ichthyornis between Gansus and Hesperornis + Baptornis.

By contrast, in the LRT Ichthyornis (Fig 1) nests with Changzuiornis (Fig 3). These nest with Juehuaornis. These nest with Apsaravis, These nest with Yanornis at the base of the Ichthyornis clade. Hesperornis is not closely related, but is derived from Archaeopteryx lithographica (the London specimen), one of the nine Solnhofen birds tested in the LRT. Benito et al tested only one Solnhofen bird.

References
Benito et al (5 co-authors) 2022. Forty new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds. PeerJ 10:e13919 DOI 10.7717/peerj.13919
Marsh OC 1872. Notice of a new and remarkable fossil bird. American Journal of Science
4(61):344–380 DOI 10.1080/00222937308696770.