Triassic revolution?

Benton and Wu 2022 considered several factors
affecting the return of life following the Permian – Triassic extinction event, (Fig 2) universally considered the worst extinction event of all time. Pertinent abbreviations include:

PTME – Permian-Triassic Mass Extinction – 251 mya (= Siberian traps)
CPE – Carnian Pluvial Episode – 231 mya (= widespread arid to rainfall)
ETME – End Triassic Mass Extinction – 200 mya (= Mid-Atlantic volcanoes)

MMR – Mesozoic Marine Revolution, (= the increase in shell-crushing and boring predation starting in the Early Triassic.

One factor Benton and Wu omitted
was the near complete absence of Permian marine vertebrates in the fossil record (Figs 1, 2). That’s 47 million years of virtually absent taxa.

According to Benton and Wu 2022,
“Marine predatory vertebrates show spectacular and rapid diversifications in the Early and Middle Triassic, and new discoveries from China have confirmed their early start in the Triassic, but not in the Late Permian.”

Or was this a geological illusion? There was a new dawn for animals following the PTME. We know which clades survived. Where did the survivors find refuge? Unfortunately, this topic is rarely to never covered, perhaps because those rare refugia have never been discovered or described. Extinction events garner headlines and take the spotlight.

Figure 2. Chart from Benton and Wu 2022. Overlay notes the absence of Permian marine vertebrates. They had to have been present Their absence is conspicuous here, but overlooked by the authors.

From another point of view
that ‘spectacular and rapid diversification‘ in the Triassic was at least partly due to the current paucity of marine fossils in the Permian (Figs 1, 2) and a relative trove of marine fossils in the Early Triassic. Blank spaces (Fig 2) can still provide data based on phylogenetic bracketing with a large gamut cladogram, like the large reptile tree (LRT, 2119 taxa, subset Fig 3).

Figure 3. Subset of the LRT focusing on ichthyosaurs and kin color coded according to chronology from the early Permian to the Cretaceous.

As an example:
here (Fig 3) the currently unknown pre-Triassic ancestors of ichthyosaurs and thalattosaurs would have to have been coeval with known and related Early Permian mesosaurs. Unfortunately all we have are two Middle Triassic late-surviving basal pachypleurosaurs and pre-pachpleurosaurs, Honghesaurus and Anarosaurus. That’s too few. Way too few for 47 million years. Where are all the Early to Late Permian marine fossils?

One answer: The late-surviving representatives of missing Permian taxa are present in the Early and Middle Triassic according to the LRT. That’s a clue that primitive relatives of Early Triassic taxa were present in the Permian.

There are no large phylogenetic gaps in the LRT.
It documents a continuous gradation phyogenetically, but not chronologically due to the patchy fossil record in general. That also means Benton’s and Wu’s “spectacular and rapid diversificaiton” might actually represent a chronological illusion. In other words, with phylogenetic bracketing the wealth of Early Triassic ichthyosaurs and pre-ichthyosaurs likely arose sometime during the Early Permian. So far we’ve only found late survivors in the geologically richer Early and Middle Triassic strata. If so marine predators, including ichthyosaurs, had a slower, steadier, more typical radiation and evolution.

We haven’t found many Permian marine vertebrate fossils yet.
Perhaps they weren’t fossilized. Perhaps those strata are not present. Perhaps those strata await discovery buried under other sediments. At times like this it’s smart to remember, in general fossils from all eras are extremely rare and often restricted to tiny pin points on the Earth’s surface skipping large swathes of geological time. That’s just the way it is.

Figure 4. Middle Triassic Atopodentatus compared to more primitive sister taxa, Permian Adelosaurus and Claudiosaurus to scale.

Overlooked by Wikipedia, Benton and Wu and saved ’til now,
there are several Permian marine and semi-marine younginiforms known from the late Permian. These include Claudiosaurus. Adelosaurus (Fig 4) and related late survivors of a Carboniferous radiation. They likewise had larger, more derived Triassic ancestors, like Atopodentatus (Fig 4).

Figure 5. Giant Cymbospondylus youngorum (Sanders et al. 2021) does not appear until the Middle Triassic. Wumengosaurus is a late survivor known from Middle Triassic strata, but phylogenetically must have had its genesis in the Permian.

Benton and Wu 2022 cited
Sanders et al. 2021 who reported on a giant ichthyosaur, Cymbospondylus youngorum (Fig 5). The authors reported, “The animal existed at most 8 million years after the emergence of the first ichthyosaurs, suggesting a much more rapid size expansion that may have been fueled by processes after the Permian mass extinction.” Benton and Wu considered this “a prime example of an ‘early burst’ radiation.“

That’s only 3 million years past the Early Triassic or 35 milllion years past the Early Permian, when pre-ichthyosaurs had their roots. How fast ichthyosaurs evolved is left up to the vagaries of the poor Permian marine fossil record vs the rich Triassic marine fossil record known to geology at present.

Figure 6. The naked mole rat, Heterocephalus, has has only a few long sensory hairs that likely help it sense the tunnel walls. These provide no insulation, as in burrowing basal cynodonts first sprouting similar hair.

On land, Benton and Wu remind us,
“the Triassic was marked by a posture shift from sprawling to erect, and a shift in physiology to warm-bloodedness, with insulating skin coverings of hair and feathers.”

The authors consider the origin of hair in Permian synapsids as “an insulating pelage”. Before hair can act as insulation it must be thick enough covering a broad enough area. So the genesis of sparse and individual hairs (Fig 6) must have had some other use that enhanced survival. Perhaps the burrowing naked mole rat, Heterocephalus, can give us some insight into the origin of individual hairs first appearing in burrowing cynodonts, retained in mole rats by either a deep time reversal or neotony from ‘hairless’ newborns, or both as ontogeny recapitulates phylogeny. Yes, this is what some cynodont skin looked like.

Benton and Wu report,
“Pterosaurs, the sister group of dinosaurs, also have dermal insulating structures commonly
called pycnofibres.”

Pterosaurs are not the sister group of dinosaurs. The omitted ancestors and non-volant cousins of pterosaurs, like Sharovipteryx (Fig 7), also have dermal insulating, heat-radiating and decorative structures.

Figure 7. Note the neck skin (integument) of Sharovipteryx, a pterosaur sister.

Benton and Wu continue,
“even if researchers balk at calling pycnofibres feathers, it does not change the fact that insulating dermal structures appeared in the first dinosaurs and the first pterosaurs, and the shared ancestry of these two clades is dated to the Early or early Middle Triassic.”

Fact? Insulating dermal structures appeared in the first dinos and pteros? Yes, for pterosaur ancestors like Cosesaurus in the Middle Triassic. No, for dinosaurs like Herrerasaurus, also in the Middle Triassic. Benton has a long history of omitting taxa related to pterosaurs recovered by Peters 2000a, b. Paleo academics at large (any exceptions?) continue to do the same.

References
Benton MJ and Wu F 2022. Triassic Revolution, Frontiers in Earth Science (2022). DOI: 10.3389/feart.2022.899541
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Sanders et al. (6 co-authors) 2021. Early giant reveals faster evolution of large body size in ichthyosaurs than in cetaceans. Science374 (6575): DOI: 10.1126/science.abf5787

wiki/Permian
wiki/Triassic

A new and bigger ‘Cymbospondylus’ enters the LRT

https://www.syfy.com/syfy-wire/an-early-triassic-ichthyosaur-was-the-earliest-known-giant

The Princeton Field Guide to Pterosaurs by Gregory Paul 2022

A while back,
paleontologist Greg Paul let me know about his new Princeton Field Guide in prep, this one about pterosaurs (Fig 1). Paul is widely acknowledged as the early leader in creating reconstructions of dinosaurs and other animals by strictly adhering to their skeletal traits and proportions.

Paul’s newst Field Guide was published June 7, 2022 with little fanfare.
I only heard about it yesterday via an off-hand blogpost comment that did not mention the book or author by name. Knowing what was in the pipeline, a keyword search was enough to find the book online. Barnes and Noble, Amazon, even Target all advertise it.

Figure 1. Cover illustration from Paul 2022. The shallow wing chord is correct. So are the uropatagia. I see little to no propatagia here as the humeri appear to extend laterally.

From the publisher’s description:
“Once seen by some as evolutionary dead-enders, pterosaurs were vigorous winged reptiles capable of thriving in an array of habitats and climates, including polar winters. The Princeton Field Guide to Pterosaurs transforms our understanding of these great Mesozoic archosaurs of the air. This incredible guide covers 115 pterosaur species and features stunning illustrations of pterosaurs ranging in size from swallows to small sailplanes, some with enormous, bizarre head crests and elongated beaks. It discusses the history of pterosaurs through 160 million years of the Mesozoic—including their anatomy, physiology, locomotion, reproduction, growth, and extinction—and even gives a taste of what it might be like to travel back to the Mesozoic. This one-of-a-kind guide also challenges the common image of big pterosaurs as ultralights that only soared, showing how these spectacular creatures could be powerful flappers as heavy as bears.”

This field guide features
115 different kinds of pterosaurs as skeletal drawings and full-color life studies. It covers pterosaur biology and the colorful history of pterosaur paleontology. Surprisingly I am listed in the ‘Acknowledgments’ section.

Let’s look inside the first few pages… The Preface
Paul is an engaging writer who draws the reader in with his literary conceit as a ‘mysterious time traveler’ both ‘startled’ and ‘delighted’. Paul described the ‘surreal’ variety in head crests.

Unfortunately Paul errs and promotes myth
1. when he describes Quetzalcoatlus (Fig 2) as, ‘the largest flying creature possible.’
2. when he calls pterosaurs distant archosaur relatives of birds.
3. when he reports, “Remaining frustratingly unresolved are the origins of pterosaurs.”

History of discovery and research section
Paul’s account is accurate and reminds one of how few and far between pterosaur papers appeared prior to the 1970s. This is when Paul estimated mass for Quetzalcoatlus (Fig 2). He reports, “My calculation that the biggest pterosaurs must have weighed much more than the biggest living ground birds (Paul 1991, 2002) was initially controversial, but it has since become widely accepted.”

If I’m not mistaken, this was Paul’s last contribution to pterosaur research. He has not participated in any phylogenetic studies, nor is he a co-author on any discoveries. Let me know if this is an error and I will correct it.

Figure 2. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale. Compare one leg of Quetzalcoatlus to the 175 pound ex-president to estimate its total weight.

History of discovery and research section continued.
“And the old classic Pteranodon underwent a notable revision with the realization that it had a major overbite, with the lower beak markedly shorter than the upper.”

The is true, but only for some Pteranodon species (Fig 3), not all. Paul should have known this before writing his book.

Figure 3. Click to enlarge. Some Pteranodon have a longer rostrum than mandible. Others don’t. Paul doesn’t know this. Any author writing about pterosaurs should know this.

Paul continues his history of discovery and research.
“What has not yet shown up is fossils of protopterosaurs because suitable fine-grained lake or lagoon bottom deposits… are not known”

This is incorrect. We have pterosaur ancestors back to Cambrian worms in the large reptile tree (LRT, 2119 taxa). Proximal Middle Triassic ancestors include Cosesaurus (Fig 4, Peters 2000). Relatives of the fenestrasaur radiation include Sharovipteryx and Longisquama (Fig 4). Each of these are found in such fine-grained sediments that jellyfish, insects and soft tissue are preserved or molded. Paul should have known this before writing his book.

Unfortunately Paul has never constructed a phylogenetic analysis. Like Paul, I was once a paleo artist, but I learned that a phylogenetic analysis answers so many questions and resolves every enigma with authority. No more wondering.

Figure 4 from 2011. Lepidosaurs tanystropheids and fenestrasaurs in the phylogenetic lineage preceding the origin of the Pterosauria.

Paul continues his history of discovery and research.
“The evolution of human understanding of pterosaurs has not undergone as dramatic a transformation as has our view of dinosaurs over the last quarter millennium.”

This is incorrect as figure 4 shows. Paul should have known this before writing his book.

Paul 2022 – What is a pterosaur?
Paul relies on ‘the great majority of researchers’ who also throw up their hands in frustration, not willing to examine the taxa in figure 3. This is a surprising action given Paul’s earlier fame at breaking with consensus based on his own research. Instead here Paul relies on the literature. He writes, “There has been considerable speculation as to which archosaurs the pterosaurs are most closely related to.”

This is the problem. Pterosaurs are not and have never been archosaurs. So let’s stop looking there and look elsewhere (Fig 4). Like Witton before him, Paul should have known what pterosaurs were before writing his book. Presently Paul is 22 years behind the times (Peters 2000) and promoting invalid myths.

“Pterosaurs had a simple dinosaur-type ankle.”

Never, ever rely on a single character to define a clade. That’s called ‘Pulling a Larry Martin.” Pterosaurs developed this ankle-type by convergence. The old ankle fetish among paleontologists goes back several decades and is now rarely brought up. Why focus on the ankle when pterosaurs have a giant finger four? Where else do we find finger four larger than three or five? Not in archosaurs. See figure 3 where each taxon in turn share a longer suite of traits with pterosaurs including a longer finger four.

Paul describes
the extreme elongation of ‘an outer finger’, apparently unable to determine if it is the fourth following the three free fingers, all bearing the typical reptile/lepidosaur number of phalanges. Paul reports, “The chest features a large sternal plate…lacking the deep bony keel. There is no wishbone furcular“. (= conjoined clavicles).

The pterosaur sternal complex is actually composed of co-ossified clavicles, a single sternum overlapping an interclavicle (Fig 5). We’ve known that since Wild 1993. Archosaurs don’t have interclavicles. Lepidosaurs do. Paul fails to mention the strap-like scapula and locked-down stem-like coracoid that indicates bipedality and flapping, as in birds. Paul should have known this before writing his book.

Figure 5. Lepidosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.

Paul mentions the prepubis,
but fails to note its significance or distribution (Fig 4). He also notes the long slender ilium, but fails to note its significance or distribution (Fig 4). Paul reports, “the foot was plantigrade.” Sometimes that was so. Other times, no (Peters 2011). Paul reports, “pterosaur eggs were soft-shelled”, but he fails to note that significance. Lepidosaurs have similar soft shells and the mother keeps them within her body longer, sometimes until just prior to hatching. Paul should have known this before writing his book.

Figure 6. Image from page 18 of Paul 2022. These are generalized taxa, not based on a strict interpretation of skeletons (Fig 7). The lowest taxon is Megalancosaurus, not Longisquama. Greg Paul, uncharacteristically, is using freehand drawings to generalize prehistoric animals rather doing what Greg Paul has taught us all: to stick to the skeleton.

Moving into phylogeny again, Paul writes,
“There does not seem to be a great division within the Pterosauria in which two or more distinct groups split apart soon after the initial appearance of the group.”

This is wrong. According to the large pterosaur tree (LPT, 262 taxa) that phylogenetic split occurred in the Late Triassic when Preondactylus (Fig 7) became the last common ancestor of the fragile-skulled, dimorphodontid-anurognathid clade of insect-eaters. On the other branch, Eudimorphodon (Fig 7) was the last common ancestor of all other pterosaurs, the robust-skulled fish-eaters. A phylogenetic analysis would have been helpful here, rather than relying on a vague notion from the extremely flawed (due to taxon exclusion) literature. That way Paul would have been able to tell his readers that the pterodactyloid grade appeared five times by convergence (4x according to Peters 2007. A 5th was recently added). Here again, Paul should have known this before writing his book.

Figure 7. Skeletal studies of the taxa in Paul’s drawing in figure 6. If you want to know what Longisquama looked like see figure 3.

Paul mistakenly writes,
“No known pterosaur was flightless.”

Actually a variety of pterosaurs were flightless. These include his favorite giant pterosaurs. Paul should have known this before writing his book. Perhaps Paul remembers his time with inventor and engineer Paul Macready who sent a mechanical Quetzalcoatlus flying, but only by cheating its proportions (Fig 8).

Figure 8. Paul MacCready’s flying pterosaur model had longer wings than Q. sp., with its vestigial distal wing phalanges. Here the model and its inspiration are shown to the same length.

Gee, I wish Greg had touched base while writing his book
just once so I could have suggested new directions and help him avoid omissions. Then I could have earned that Acknowledgements mention. As is, this book comes as a disappointing rehash of old and discredited pterosaur myths. Missing here is the spirit and drive of the brilliant, young Greg Paul, the one we leaned from so many decades ago, the one who saw things precisely, sometimes differently than “the great majority of researchers” he now leans on.

References
Paul GS 2022. The Princeton Field Guide to Pterosaurs. Princeton Field Guides. Online.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.
Peters D 2000b. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification
Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.

What exactly IS a pterosaur? – part 3 of 3

The evolution of the ‘spiracular region’ in Shuyu, a tiny galeaspid without a spiracle

Gai et al. 2022 discuss their views
on the origin of the vertebrate spiracular region in Shuyu (Gai et al 2011, Middle Silurian; Fig 1), a tiny galeaspid lacking a spiracle (Fig 2) in a clade lacking spiracles (Fig 3).

Galeaspids were the only vertebrates
to migrate their primitive immobile oral cavity to the dorsal skull (Figs 1, 3). Ecollogically galeaspids appear to have been flattened, sit-and-wait filter feeders, hiding while buried in sandy sediments with only their dorsal surface and oral cavity exposed.

Note: There is no galeaspid named Galeaspis. That’s a trilobite.

Also note: Paleo fish workers don’t yet understand there were two origins for jaws in vertebrates. Galeaspids were not in the gnathostome lineage. Rather their proximal outgroup taxon, Drepanaspis (Fig 3), was also basal to placoderms. Note the gradual migration of the terminal oral cavity to the dorsal surface. Primitive galeaspids retain a transverse oral cavity and lateral eyes. Derived galeaspids developed skull processes, migrated the eyes dorsally and the oral cavity evolved to become circular, then slit-shaped at right angles to the original orientation. Very strange.

Also note: Despite their bony and immobile head plates, galeapids were not related to osteostracans, like the pre-sturgeon, Hemicyclaspis (Fig 4 frame 4). Lampreys, osteostracans and sturgeons all retained a ventral oral opening.

Figure 1. Modified from Gai et al 2022 showing the tiny galeaspid, Shuyu (Gai et al 2011), in dorsal view with the gill chambers exposed. The first gill chamber evolves to become the spiracle.

Gai et all 2011 dismiss the hypothesis
that osteostracans were the closest jawless relative of the gnathostomes because, “their massive, mineralized braincase has a median nasohypophyseal organ resembling the condition in lampreys.”

By contrast, descendants of lampreys (Pteromyzon) in the large reptile tree (LRT, 2119 taxa, subset Fig 6) split into two clades: 1) hard-headed arandaspids, galeaspids and placoderms; and 2) soft-headed Jamoytius, Birkeria, Haikouichthys, hard-headed Hemicyclaspis, semi-hard-headed Thelodus, hard-headed sturgeons and gnathostomes. Both clades evolved their own jaw. Past efforts at describing or discovering the evolution of jaws have failed due to not recognizing the dual and convergent genesis of jaws that comes from adding taxa.

Figure 2. Cownose ray feeding by dropping their cephalic lobes to increase the suction on their oyster prey.

The spiracle is a small opening in the temple region
of rays (Fig 2), sawfish and other flattened, bottom-dwelling, cartilaginous fish. With the ventral mouth buried in silty sediment the spiracle serves as an alternate water intake for respiration. It is also the ear hole in tetrapods. Traditionally the spiracle is homologous with the first gill opening in lamprey-grade and higher chordates (Fig 1). The spiracle is lost in hammerhead sharks and many bony fish (Fig 4). Galeaspids and kin (Figs 1, 4) do not have a spiracle. Their first gill chamber (Fig 1) is not different from the other gill chambers.

Figure 3. Proposted evolution within Galeaspida, starting with Drepanaspis, a taxon not mentioned in galeaspid studies. Note the lack of a spiracle or jaws in any of these bottom-dwelling, filter-feeding taxa. Blue arrows point to oral opening and away from gill exits. Red dots are eyeballs.

From the Gai et al 2022 abstract
“The spiracular region, comprising the hyomandibular pouch together with the mandibular and hyoid arches, has a complex evolutionary history”.

Perhaps more complex than Gai et al realize due to their not recognizing the dual origin of jaws (placoderms and gnathostomes by convergence) in vertebrates (Fig 1). Adding taxa resolves this issue.

Figure 4. This is figure 9 from Gai et all 2022 split to fit this format, then captions moved to the graphic, then skulls removed from the graphic, then adjusted to match the LRT topology.

From the abstract
“Here we present the first confirmed example of a complete spiracular gill in any vertebrate, in the galeaspid (jawless stem gnathostome) Shuyu. Comparisons with two other groups of jawless stem gnathostomes, osteostracans and heterostracans, indicate that they also probably possessed full-sized spiracular gills and that this condition may thus be primitive for the gnathostome stem group”.

No. Gnathostomes (= Chondrosteus (Fig 4) and descendants) developed jaws apart from placoderms. Shuyu is not a stem gnathostome. Sturgeons are pre-gnathostomes.

“This contrasts with the living jawless cyclostomes, in which the mandibular and hyoid arches are strongly modified and the hyomandibular pouch is lost in the adult”.

Living lampreys are 500 million years away from that last common ancestor that ultimately split into the placoderm and gnathostome clades. So living lampreys can be highly modified from their Cambrian ancestors.

“On the basis of these findings we present an overview of spiracular evolution among vertebrates.” [See figure 4 frame 1.]

Gai et al. almost have a valid phylogenetic topology (Fig 4). It is missing just a few elements. Do not proceed on your own studies without a valid cladogram. Otherwise all your subsequent hypotheses are prone to crack and possibly crumble.

Gai et al. 2022 report,
“Our new evidence indicates that the so-called interbranchial ridges of galeaspids are actually the dorsal portion of branchial arches. They are incorporated into the neurocranium to form a massive skull as assumed in osteostracans by Stensiö.

By contrast, in the LRT (subset Fig 6) these two bone-headed fish clades (galeaspids and osteostracans) are not related. This is yet another example of convergence not recognized by the authors. Don’t make the same mistake. Create your own LRT so you, too, will have a panoramic view of all vertebrates. Don’t focus too much on one clade or another. You’ll miss something by convergence on the outskirts and the LRT will catch it.

“Compared to osteostracans, the entire branchial apparatus in Shuyu retains a general vertebrate condition, thus, it is easy to identify the mandibular and hyoid arches according to their topological position and nerve innervation.”

Shuyu nests close to the base of the Vertebrata in the LRT. So it should retain a general condition.

Figure 5. Cheiracanthus was examined, scored and added to the LRT during the course of this study.

Gai et al. 2022 introduced
a well-known acanthodian in their cladogram (Fig 4), Cheiracanthus (Egerton 1861, Middle Devonian, Fig 5), not previously tested in the LRT. Here Cheiracanthus is traced, scored and nested with Homalacnathus at the base of the acanthodians, which is at the base of the clade the ultimately produced lobe-fin fish and tetrapods. So it’s a human ancestor, but not a tuna ancestor.

Figure 6. Subset of the LRT focusing on basal vertebrates. Note the dual origin of jaws in placoderms and gnathostomes.

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

PS
What drives the stream of water carrying food and oxygen in a galeaspid? The mouth doesn’t move and it is not pointed anteriorly. The gills don’t move within the solid skull. The soft tissue atrium must be able to shrink and expand like a bellows within the solid skull. The galeaspid skull is open ventrally to permit the expansion of this gular sac (Fig 7, 8). It does not include an open mouth and gill slits, as in unrelated, but often convergent osteostracans.

Figure 7. The streamlined galeaspid, Rhegmaspis xiphoidea IVPP V 19354.3

Added the morning after publication:
Rhegmaspis (Figs. 7, 8) is a streamlined galeaspid. Nochelaspis and Platylomaspis (Fig 8) are large galeaspids often reconstructed with ventral oral and gill openings, like osteostracans. I don’t see those traits here (Fig 8). Rather the ventral portion appears to have been soft tissue, a gular sac that expanded and contracted to drive inhalation and exhalation along with water borne tiny food particles. In other words these are the only fish with a mouth on top of the skull. Nares are not present, but a pineal opening often is present. All this points to a lifestyle not of predation, but of sit-and-wait filtration.

Figure 8. Regmaspis (see figure 7) compared to Nochelaspis and Platylomaspis, two large ‘galeaspids’ with a ventral mouth and gill openings, like those in osteostracans, different from those in other galeaspids. The dorsal median naris is much smaller than in galeaspids, similar to the naris in osteostracans.

References
Egerton P de MG 1861. British fossils, pp 51-75 in Huxley TH (ed), Preliminary Essay Upon the Systematic Arrangement of the Fishes of the Devonian Epoch, Figures and Descriptions Illustrative of British Organic Remains. Memoirs of the Geological Survey, U.K, (Decade 10).
Gai Z et al 2011. Fossil jawless fish from China foreshadows early jawed vertebrate anatomy. Nature 476:324–327.
Gai Z. Zi M. Ahlberg PE and Donoghue PCJ 2022. The Evolution of the Spiracular Region From Jawless Fishes to Tetrapods. Font. Ecol. Evol., 19 May 2022 | https://doi.org/10.3389/fevo.2022.887172

wiki/Cheiracanthus
wiki/Spiracle
wiki/Galeaspida
wiki/Shuyu

Tiny Phyllodontosuchus lufengensis enters the LRT alongside tiny Coloradisuchus

Harris et al 2000 described and named
a “leaf-toothed crocodile,” Phyllodontosuchus lufengensis (Sinermurian, Early Jurassic China, 200mya, BVP568-L12, Fig 1), based on the middle and posterior teeth. The anterior teeth remained recurved and sharp. The tiny skull is 7cm (less than 3 inches) long. The authors considered this taxon a sphenosuchian crocodylomorph without conducting an analysis.

After analysis in the LRT (subset Fig 3), Phyllodontosuchus nests elsewhere, apart from Sphenosuchus and kin.

Figure 1. Phyllodontosuchus skull from Harris et al 2000. Colors added here. Shown twice life size @72dpi.

Harris et al reported,
“Unfortunately, much of the detail in the only known skull of Phyllodontosuchus is not discernable due o nuances of preservation, including similarity of the bone to the surrounding matrix. Nevertheless, enough detail is preserved to permit diagnosis.”

Using colors (Fig 1) enough detail can be gleaned to score Phyllodontosuchus.

Harris et al thought
the premaxilla was not preserved.

Colors helped to identify the premaxilla here (yellow Fig 1). The naris is terminal and breaks the jawline, as in equally tiny Coloradisuchus (Fig 2). That can be confusing.

Harris et al thought
“no sutures are discernable in any fragment”.

Maybe they should have colored the bones between the sutures using DGS (Fig 1).

Harris et al thought
“Crushing has apparently filled in the supratemporal fenestrae, and their outlines are likewise indeterminate.”

Digital graphic segregation (Fig 1) was able to discern these structures.

The authors focused their attention on the teeth,
comparing them to herbivorous dinosaurs and other archosauriforms. Harris et al more or less correctly concluded the specimen “shows more similarities with the basal Crocodylomorpha (Sphenosuchia) than any other.”

Figure 2. Coloradisuchus half-skull from Martinez, Alcover and Pol 2017. Colors added. Shown life size @72dpi. Restoration based on Dibrothosuchus, which is off a node or two.

After reconstruction and analysis
in the large reptile tree (LRT, 2118 taxa) Early Jurassic Phyllodontosuchus nested with Late Triassic Coloradisuchus (Fig 2), a taxon not described until Martinez, Alcober and Pol 2017. These taxa nest between Gracilisuchus and Scleromochlus + Saltopus + Lagosuchus as basal bipedal members of the Crocodylomorpha. The latter two taxa are known from post-crania only, which don’t resolve with skull-only taxa Phyllodontosuchus and Coloradisuchus. In order for complete resolution in the LRT either the skull-only or the skull-less taxa must be left out.

Figure 3. Subset of the LRT focusing on Crocodylomorpha. Adding taxa and rescoring earlier entries moves a few taxa to new nesting sites here.

Unfortunately
the tiny, bipedal crocodylomorphs, Gracilisuchus, Scleromochlus, Saltopus and Lagosuchus are not often, if ever, included in other crocodylomorph studies. The LRT, which tests taxa together that have never been tested together, indicates that traditional omission needs to change. Simply add these taxa (and more) to your croc studies to see for yourself how well they fit in. Then let us know what you get.

PS
Martinez, Alcober and Pol 2017 mistakenly considered Coloradisuchus “a new protosuchid crocodiliform.” Unfortunately, Phyllodontosuchus, Gracilisuchus, Scleromochlus, Saltoposuchus and Lagosuchus were not mentioned in the text. Protosuchus nests elsewhere in the LRT.

References
Harris JD et al 2000. A new and unusual sphenosuchian (Archosauria: Crocodylomorpha) from the Lower Jurassic Lufeng Formation, People’s Republic of China. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 215(1): 47–68.
Martinez RN, Alcober OA and Pol D 2017. A new protosuchid crocodyliform (Pseudosuchia, Crocodylomorpha) from the Norian Los Colorados Formation, northwestern Argentina. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1491047.

wiki/Coloradisuchus
wiki/Phyllodontosuchus
wiki/Saltopus
wiki/Lagosuchus
wiki/Gracilisuchus
wiki/Scleromochlus

Bird evolution: plover > crane > hamerkop > hornbill > toucan > barbet > quetzal

A recent FB post by U of Maryland dinosaur professor, Thom Holtz,
wrote hornbills and toucans arose by convergence on opposite sides of the Atlantic.

We looked at that situation earlier (Fig 1) in 2017.

Figure 1. South America and Africa during the Albian, 100 mya. This is when toucans and hornbills must have separated.

By contrast,
the large reptile tree (LRT, 2118 taxa) nests hornbills with toucans. After their last common ancestor in the Cretaceous drifting continents slowly separated them. Early Cretaceous Archaeorhynchus is the most primitive crown bird, so crown birds radiated throughout the Cretaceous. Their fossils await discovery.

In support of that hypothesis,
images of taxa related to toucans and hornbills are presented to see the course of evolution documented in detail by the LRT. You might find this easier than searching through 400,000 matrix scores that nobody really wants to sit down to review. The LRT is fully resolved and continually tested and updated.

Figure 2. Evolution of birds from plover to quetzal according to the LRT.

Evolution always always works in small steps.
So here (Fig 2) are the small steps currently tested in the LRT documenting the origin of the highly derived quetzal (genus: Pharmachrus) from predecessor taxa going back to basal shorebirds like the plover (genus: Charadrius).

Every time a new taxon nests between two established taxa,
on average that halves the phylogenetic distance between them. So adding taxa is key to understanding evolutionary directions and processes by reducing the phylogenetic distance between all included taxa.

Figure 3. Hamerkop (Scopus) hatchlings of various ages. Note the legs are shorter than in the adult, Fig 2

Smaller, shorter-legged birds can arise
from long-legged cranes by neotony because their hatchlings (Figs 3, 4) typically, perhaps universally, are smaller with shorter legs. The above plover to quetzal clade (Fig 2) in general evolved first by gaining size and leg length, then by phylogenetic miniaturization, getting smaller with shorter legs. The beak stayed large and got larger in hornbills and toucans, then became gradually smaller in barbets, tropicbirds, mousebirds and quetzals.

Figure 4. Hornbill and toucan hatchlings. Note the short bills. These are retained by neotony in adult descendant taxa like the barbet, tropicbird, mousebird and quetzal.

Larger, longer-legged birds arise
from marginally taller shore birds marginally able to forage in deeper and deeper waters, away from the shorter shallow-water dippers, probers and waders. (This is how certain flightless pterosaurs became giants).

Phaethon, the tropicbird,
seems to have experienced a reversal back to gulls. Note how it reverts to the color, niche and design of an ancestral gull, Chroicocephalus. It soars over wide expanses of open water. Otherwise derived taxa in this clade continue to make the jungle their home, retaining bright colors, long tail feathers and spending time perching rather than soaring.

Figure 5. Cariama compared to Sagittarius. The former is closer to flamingos. The latter is closer to terror birds. Both are close to trumpeters.

Professor Holtz also wrote on FB,
that seriemas (genus: Cariama, Fig 5) and secretary birds (genus: Sagittarius, Fig 5) also arose by convergence on opposite sides of the Atlantic. After testing in the LRT, African Sagittarius is basal to the South American terror birds, a position traditionally held by South American Cariama, which is a sister to the tropical (= South American and African) flamingo, Phoenicopterus. So these long-legged birds are all closely related. The long-legged and poor flying Amazon trumpeter, Psophia, currently nests between them.

Currently there is a problem with deep time cladograms based on genes
accepted at the university level and taught by professors to naive, but eager-to-learn, tuition-paying students. Professors teach what they know, and most of what they know they read somewhere, usually in a Benton textbook or academic publications. Longtime readers know that all too often taxon exclusion and four other problems (listed below) invade current academic papers. It’s rampant enough that this blogsite is approaching 4000 blog posts. These five problems plaguing paleontology have been ignored and approved by referees and editors who don’t know any better because they, too, are working from what they read somewhere, ultimately becoming part of the consensus, whether right or wrong.

That’s why I continue to encourage all readers
to build your own cladogram so you won’t suffer from the dogma of repeating what you read somewhere. Instead you’ll have the knowledge that comes from testing with unbiased software. This is the only way you are going to discover something, other than to get really lucky and dig something up, somewhere on the planet that hasn’t already been dug up.

The top five problems plaguing paleontology:
Number one: taxon exclusion.
Number two: borrowing untested cladograms.
Number three: trusting genomic results.
Number four: trusting textbooks and academic traditions.
Number five: freehand reconstructions.
Solution: Keep adding taxa to your own trait-based cladogram. Trace specimens with transparent colors and from those tracings create more accurate and verifiable reconstructions.

Palaeobates enters the LRT between two species of Hybodus

This is one of the first taxa
to have a convex bony-fish face lacking a shark-like long rostrum and underslung jaws. That means Palaeobates is an overlooked human ancestor.

Figure 1. Palaeospondylus in situ. Colors and reconstruction added here. The nasals have fallen, like a drawbridge, in situ, repaired in the reconstruction.

Palaeobates angustissimus
(Meyer 1849; Early Triassic, NMC 9980, originally Strophodus angustissimus Agassiz 1834) is a transitional taxon between one Hybodus species and another. The skull was relatively smaller, the post-crania longer and the fins more robust.

Figure 2. Fish evolution from Hybodus to Amia documenting the shark to bony fish transition.

The more primitive relative,
Hybodus fraasi, retained the primitive nasal extending beyond the jaws, typical of most sharks. By contrast, the more derived Hybodus basanus had a short-nosed morphology, retained by most more derived bony fish. Palaeobates is the transitional taxon between the two.

Only a few reversals among bony fish,
like Orthocomus, Protosphyraena, swordfish and sailfish redevelop a long rostrum with underslung jaws. A few readers will note that humans (genus: Homo) also display this reversal with a shark-like nose extending beyond the jaws.

References
Meyer H v 1849. Fische, Crustaceen, Echinodermen und andere Versteinerungen aus dem Muschelkalk Oberschlesiens. Palaeontographica, 1: 216-242.

wiki/Hybodus
wiki/Orodus
wiki/Palaeobates

Gatesy et al. continue to spread the myth of cetacean monophyly

Here it is Spring 2022
and academics are still beating the dead hypothesis of a transition within whales from teeth to baleen. Odontoceti is not related to Mysticeti. They are ‘whales’ by convergence. Gatesy et al. (8 co-authors) 2022 just can’t let the old invalid hypothesis of a monophyletic ‘Cetacea’ go. They don’t want to add the pertinent taxa that split the Cetacea in the large reptile tree (LRT, 2118 taxa, subsets Fig 1) back in 2016.

Figure 1. Two subsets of the LRT focusing on odontocetes and their ancestors (above) and mysticetes and their ancestor (bottom) from several years ago. A few taxa have been added to the LRT since posting this.

Gatesy et al. report,
“The transition in Mysticeti (Cetacea) from capture of individual prey using teeth to bulk
filtering batches of small prey using baleen ranks among the most dramatic evolutionary
transformations in mammalian history. We review phylogenetic work on the homology of
mysticete feeding structures from anatomical, ontogenetic, and genomic perspectives.”

This is a bogus statement. There was no “transition in Mysticeti (Cetacea) from capture of individual prey using teeth to bultk filtering batches of small prey using baleen.” Without a valid phylogenetic context (Fig 1) everything else in this study is as meaningless as attempting to map the transition from bats to birds.

References
Gatesy et al 2022. Anatomical, ontogenetic, and genomic homologies guide
reconstructions of the teeth-to-baleen transition in mysticete whales. bioRxiv preprint doi: https://doi.org/10.1101/2022.03.10.483660
Peters D unpublished. PDF on ResearchGate.net

Other posts with links to older posts:

Bisconti and Carnevale 2022 discuss the origin of baleen whales while omitting the ancestors of baleen whales

Whales are diphyletic. Goodbye ‘Cetacea’!

A cautionary tale: ‘The position of Cetacea within Mammalia’ by O’Leary and Geisler 1999.

Eastmanosteus, another biting placoderm, enters the LRT

Placoderms are different from the rest of us
As we learned earlier, placoderms (Figs 1, 2) developed jaws by convergence (Figs 3, 4) and produced only one extant taxon, Phreatobius, a tiny, semi-terrestrial fish from the Amazon.

Figure 1. Lateral view Eastmanosteus from Johanson 2003 with bones colorized using tetrapod homologies. Dorsal view from Hanke et al 1996. Quadrate is imagined. This illustration demonstrates the need to rename all basal vertebrate facial bones with tetrapod homologs, even if only by color. Otherwise their homology will forever remain in the dark.

Here Eastmanosteus,
(Fig 1) one of the smaller arthrodire (= biting) placoderms, enters the large reptile tree (LRT, 2118 taxa, subset Fig 4) between smaller Coccosteus (Fig 2) and massive Dunkleosteus. The informative diagram provided by Johanson 2003 (Fig 1) informed several changes in tetrapod homology bone identities in placoderms. It’s a great teaching tool that clearly separates the sutures from the sensory canals that cross the bones. Similar facial bones developed independently in the thelodont > sturgeon > shark > bony fish > tetrapod lineage (Fig 3). The lack of a premaxilla, maxilla, lacrimal and squamosal is a common trait in all basal vertebrates.

Figure 2. Coccosteus is a smaller, more primtiive arthrodire placoderm. Colors updated from prior illustrations.

Eastmanosteus calliapsis enters the LRT today
(Obruchev 1963, originally Dinichthys pustulosus Eastman 1907; Middle Devonian; skull length 27cm, est body length 1.5m. Fig 1). In morphology it closely resembles Coccosteus (Fig 2).

Figure 3. The other origin of jaws from the ostracoderm, Hemicyclaspis, Thelodus, Acipenser (sturgeon) and Chondrosteus. This origin is convergent with the origin of jaws on placoderms (Fig 4).

The origin of placoderms
from armored Drepanaspis was recovered by the LRT (Fig 4) recently. The independent origin of jaws in gnathostomes and placoderms was not considered or suggested in prior studies. If so, let me know so I can promote it here.

Figure 4. Subset of the LRT focused on basal vertebrates. Note the independent and convergent origin of jaws in ganthostomes and placoderms. This has been overlooked previously.

The Zerina Johanson illustration of Eastmanosteus
(Fig 1) demonstrates the need to rename all basal vertebrate (= fish) facial bones with tetrapod homologs, even if only by color. Otherwise their homology will forever remain in the dark.

Giving credit were credit is due, Zerina Johanson is a placoderm expert.
Her YouTube lecture on Gogo Formation placoderms and lobefins (below) is wonderfully informative, but parts are a little outdated due to taxon exclusion. For instance, as we learned very recently, ptyctodontids are no longer placoderms. Changes like that happen in science when new light is shed on a subject, often by taxon inclusion in the LRT.

References
Eastman CR 1907. NY State Museum Memoir 10: 130.
Hanke GF, Stewart KW and Lammers, GE 1996. Eastmanosteus lundarensis sp. nov. From the Middle Devonian Elm Point and Winnipegosis Formations of Manitoba”. Journal of Vertebrate Paleontology. 16 (4): 606–616. doi:10.1080/02724634.1996.10011351
Johanson Z 2003. Placoderm branchial and hypobranchial muscles and origins in jawed vertebrates. Journal of Vertebrate Paleontology 23, 735–749.

wiki/Eastmanosteus
hwiki/Arthrodira
wiki/Placodermi
reptileevolution.com/dunkleosteus

SDUST V1014 and the ongoing multi-Sinopterus problem

Zhou, Yu, Zhu and Andres 2022 report on
an immature Early Cretaceous pterosaur wing from China. The specimen, SDUST V1014 (Figs 1,2) was thin sectioned to examine its bone histology and sexual maturity.

Figure 1. The SDUST V1014 specimen assigned to Sinopterus in situ from Zhou et al 2022. Full scale on a 72dpi monitor. Yes, it is small and immature based on the unfused epiphyses (= joints).

Zhou et al also noted the presence
of unfused epiphyses at the elbow, wrist and metacarpophalangeal joints. Such joints typically indicate immaturity in lepidosaurs and mammals.

According to the U of Maryland website: In the lepidosaur clade, squamata, “long bones feature distinct epiphyses and diaphyses separated by cartilaginous epiphyseal plates. Epiphyses and diaphyses fuse as the epiphyseal plate is resorbed upon full adulthood. Convergent with Mammalia. This feature typically indicated determinate growth.”

Figure 2. Reconstruction of SDUST V1014 specimen from figure 1. Full scale on a 72dpi monitor. Detached epiphyses mark this as an immature lepidosaur.

Tiny manual digit 5 was overlooked here (again)
because pterosaur workers don’t look for it (Fig 2).

Figure 3. Sinopterus atavisimus, nesting at the base of the Dsungaripterus clade (right) compared to scale with SDUST V1014, an immature specimen destined for more growth (left).

The Sinopterus problem was revealed
in the large pterosaur tree (LPT, 262 taxa, subset Fig 5) because it tests more than one specimen assigned to a genus. Note the presence of four tested taxa all claimed to be Sinopterus, at the base of four different clades. The authors mention the presence of Sinopterus atavismus (Fig 3) from the same area. In the LPT Sinopterus atavismus is a sister to SDUST V1014, but nests at the base of the Dsungaripterus clade. This rather obvious (Fig 3) hypothesis of interrelationships has been ignored by pterosaur workers who prefer to lump more and more pterosaurs into the genus wastebasket of Sinopterus (Fig 5).

Figure 4. Sinopterus skulls presented by Zhang et al. 2019.

This problem and many others
have been overlooked because academic pterosaur workers are reticient (or loathe) to add more taxa. They know they should, but they also know they can get away without doing so given the current crop of referees.

Figure 5. Subset of the LPT documenting the Sinopterus problem. Now four dispersed taxa have been labeled Sinopterus.Only the holotype is going to stay Snopterus. The other three need new names.

A phylogenetic analysis is the only way
to determine clade and genus membership. You can’t just note a trait or two (= Pulling a Larry Martin). The Sinopterus problem (Fig 3) is a case in point and a cautionary tale. The SDUST V1014 specimen does not nest with the other holotype and referred Sinopterus specimens, but at the base of the Shenzhoupterus + Nemicolopterus clade. That hypothesis of interrelationships falsifies the headline of the Zhou et al paper because this specimen is not a Sinopterus.

Don’t let problems like this happen in your studies.
Nothing should proceed in paleontology without a precise reconstruction (Fig 2) and a valid phylognetic analysis (Fig 5). Both are missing in Zhou et al. The first step is knowing what your new taxon is. Publishing mistakes should be avoided.

Build your own LRT and LPT.
Then you won’t be inclined to accept results you read, because you’ll have results you tested.

References
Zhou C-F, Yu D, Zhu Z and Andres B 2022. A new wing skeleton of the Jehol tapejarid Sinopterus and its implications for ontogeny and palecology of the Tapearidae. Nature Scientific Reports 12:10159 https://doi.org/10.1038/s41598-022-14111-2

wiki/Sinopterus
wiki/Epiphysis
geol.umd.edu/~jmerck/blepidosauria.html

Sinopterus IVPP V 23388 in detail

Ptyctodontids are not placoderms

According to Wikipedia:
“The ptyctodonts are regarded as the sister group of the Arthrodira and Phyllolepida.”

Traditionally and at university these are all considered placoderms.

“With their big heads, big eyes, reduced armor and long bodies, the ptyctodontids bore a superficial resemblance to modern day chimaeras (Holocephali)”.

I’m still looking for data to support the ‘long bodies’ description. Haven’t found it yet. Ptyctodonts (‘tic-toe-donts’) skeletons are rarely preserved and (so far) no articulated skulls have been discovered. They have to be assembled.

“Their armor was reduced to a pattern of small plates around the head and neck.”

Note the assumption, that the armor was “reduced”. That would be true only if ptyctodonts were related to placoderms. They are not.

“Like the extinct and related acanthothoracids, and the living and unrelated holocephalians, most of the ptyctodontids are thought to have lived near the sea bottom and preyed on shellfish.”

That doesn’t make sense for a clade of discoidal fish with crushing jaws lacking teeth. Instead they resemble extant coral reef dwellers, like angelfish, by analogy, not homology.

Figure 1. The evolution of Ptyctodontida in the LRT illustrated to scale. Here Robustichthys is basal to a Cheirodus clade and a Materpiscis clade.

Acanthothoracids, according to Wikipedia:
“Acanthothoraci is an extinct group of chimaera-like placoderms who were closely related to the rhenanid placoderms.”

The problem is: ray-like rhenanids, like Early Devonian Gemuendina and Late Devonian Jagornia are related to the extant manta ray, Manta when more taxa are added.

Here,
in the large reptile tree (LRT, 2116 taxa) discoidal ptyctodonts, like Campbellodus and Austroptyctodus, nest with Eurynotus, Cheirodus and other discoidal, ganoid-scaled bony fish (Fig 1).

Fish workers need to confirm, refute or correct this.

Figure 2. Cladogram from Trinajstic et al 2019 focsuing on Ptyctodontida like Campbellodus. A putative Early Devonian ptyctodont, Tollouds, appears to be a tiny, basal arthrodire placoderm based on a partial mandible here restored. Lunaspis is a flat skull placoderm, distinct from tall-skull ptyctodonts. Early Devonian Brindabellaspis nests with pre-tetrapods in the LRT, not with placoderms. The tall bone in Campbellodus is not a spine, but would have been enveloped in flesh in vivo. See figure 1.

Trinajstic et al. 2019 published a cladogram of Ptyctodontida
and their outgroups. Taxon exclusion seems to be a problem here. Note the gradual accumulation of derived traits shown in figure 1, based on the LRT. By contrast, note the lack of a gradual accumulation of derived traits in figure 2 from Trinajstic et al 2019. No outgroups are discoidal, for starters.

Trinajstic et al. 2019 reported,
“Ptyctodont remains are common in Middle to Late Devonian sediments globally, however, they occur mostly as isolated tooth plates, with body fossils being rare. Complete, articulated specimens showing three-dimensional preservation are even rarer, with three taxa known from the early Frasnian Gogo Formation in Western Australia (Austroptyctodus, Campbellodus and Materpiscis) and a single taxon, Chelyophorus from the Famennian of the Oryol Region, Russia.”

Evolution of Ptyctodontida
(Gross 1932) Traditionally considered placoderms, here Late Devonian members of this clade (Campbellodus, Austroptyctodus and Materpiscis) nest with Carboniferous to Triassic Cheirodus and Eurynotus among the bony fish close to gars and catfish. Skull bones are not reduced in ptyctodonts relative to related taxa, but postcranial ganoid scales are absent.

Robustichthys luopingensis (Xu et al. 2014; Xu 2019; Middle Triassic) was described as the largest holstean fish of the Middle Triassic. Here the clade Holostei is polyphyletic and Robustichthys nests with Hoplosternum, the armored catfish. The jugal is the original maxilla, a bone lacking here. The mandible has a tall coronoid process.

Eurynotus crenatus (Agassiz 1835; Friedman et al. 2018; Early Carboniferous, 310 mya) is widely considered a relative of Cheirodus.

Amphicentrum granulosus = Cheirodus granulosus (McCoy 1848, 1855 20cm; Carboniferous) is a disc-shaped fish lacking pelvic fins, covered in large rectangular ganoid scales. The postparietals are absent. The tabular and supratemporal are fused. The squamosal is tall. The preopercular and pelvic fins are missing. Teeth are absent from the upper jaws. Note the heterocercal tail.

Bobasatrania canadensis (White 1932; Permian–Triassic, 255–237mya) This discoidal fish from Madagascar nests with Cheirodus in the LRT.

Platysomus parvulus (Agassiz 1843, Carboniferous to Permian; 18cm long) is a taller, more disc-like fish related to Cheirodus. Note the reduction of the mandible. Probably a plankton eater.

Campbellodus decipiens (Miles and Young 1977; Late Devonian) is reconstructed here from the original diagram in Long 1997.

Austroptyctodus gardineri (right, originally Ctenurella (Miles and Young 1977; Long 1997; Late Devonian, Fig 3) appears to be toothless in the illustration above, but had tooth plates. Here it nests with Materpiscis and Campbellodus.

Materpiscis attenboroughi (Long, Trinjstic, Young and Senden 2008; Late Devonian; 28cm long est., Fig 3) is similar to Austroptyctodus and includes a single quarter-sized embryo inside indicating viviparity.

Figure 3. Austroptyctodus and Materpiscis to scale.

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

References
Agassiz JLR 1835. On the fossil fishes of Scotland. Report of the British Association for the Advancement of Science, British Association for the Advancement of Science, Edinburgh.
Burrow C, den Blaawen J, Newman M and Davidson R 2016. The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland. Palaeontologia Electronica 19.1.10A
Friedman M, Pierce SE, Coates M and Giles S 2018. Feeding structures in the ray-finned fish Eurynotus crenatus (Actinopterygii: Eurynotiformes) implicationsfor trophic diversification among Carboniferous actiniopterygians. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 109, 33–47.
Gagnier P-Y 1996. Acanthodii, p. 149-164. In Schultze, H.-P. and Cloutier, R. (eds.), Devonian Fishes and Plants of Miguasha, Quebec, Canada . Pfeil, Munich.
Long JA 1997. Ptyctodontid fishes from the Late Devonian Gogo Formation, Western Australia, with a revision of the German genus Ctenurella Orvig 1960. Geodiversitas 19: 515-555.
Long JA, Trinajstic K, Young GC and Senden T 2008. Live birth in the Devonian period. Nature 453: 650-653.
Miles RS and Young GC 1977. Placoderm interrelationships reconsidered in the light of new ptyctodontids from Gogo Western Australia. Linn. Soc. Symp. Series 4: 123-198.
McCoy F 1855. A synopsis of the classification of the British Palaeozoic rocks, with a systematic description of the British Palaeozoic fossils. Fasciculus 3, Mollusca and Palaeozoic fishes. British Palaeozoic Fossils, Part II. Palaeontology 407-666.
Trinajstic K, Long JA, Ivanov AO and Mark-Kurik E 2019. A new genus of ptyctodont (Placodermi) from the Late Devonian of Baltic area. Palaeontologia Electronica 22.2.23A 1-19. https://doi.org/10.26879/890 palaeo-electronica.org/content/2019/2490-a-new-baltic-ptyctodont

wiki/Cheirodus
wiki/Austroptyctodus
wiki/Materpiscis
wiki/Platysomus
wiki/Eurynotus – not yet posted
/wiki/Bobasatrania
wiki/Ptyctodontida
wiki/Chirodontidae – not yet posted
wiki/Acanthothoraci

https://pterosaurheresies.wordpress.com/2022/06/12/the-origin-of-placoderms-the-convergent-origin-of-jaws-in-vertebrates/