The mahi-mahi now has three bottom-dwelling descendants in the LRT

The mahi-mahi (Coryphaena hippurus, Fig. 1) is an extant open-seas predator. Descendants of Coryphaena include three sea-floor dwellers: Malacanthus (Fig. 2), Callionymus (Fig. 3) and deep-sea Notothenia (Fig. 4) according to the large reptile tree (LRT, 1956+ taxa).

Figure 1a. Coryphaena wall mount.
Figure 1a. Femaile Coryphaena skull diagram from Gregory 1933. Colors added here.
Figure 1b. Femaile Coryphaena skull diagram from Gregory 1933. Colors added here.

Coryphaena hippurus
(Linneaus 1758; 1.5m length) is the extant open seas predator mahi-mahi or dolphinfish, here related to the similar, but deeper sea Notothenia. The dorsal fin starts at the skull. The caudal fin is deeply forked. The teeth are needle-like. Males have a tall fleshy forehead supported by a bony crest. A smaller-crested female is also shown above.

Figure 2. Malacanthus the quakerfish, a slower, lower mahi-mahi descendant and a reef-dweller.

Malacanthus brevirostris
(Guichenot 1848; 30cm) is the extant quakerfish, a type of tilefish. A sharp spine grows from the operculum of this reef dweller. A traditional perciform, here Malacanthus nests between Coryphaena and Notothenia. The parietal is absent in these related taxa. They are typically living in pairs in sand burrows they have excavated. They feed on small fishes and invertebrates.

Figure 3. Callionymus, the extant dragonfish, another mahi-mahi descendant. This one buries itself in sand.

Callionymus lyra
(Linneaus 1758; 30cm) is the extant dragonet, a colorful, bottom-dwelling fish. Often buried with eyes protruding feeding on worms and crustaceans. Note the extremely large premaxilla and fused robust jugal + postorbital. The quadrate is prone. The jaws are wider than the cranium. The pelvic fins are larger than the pectorals.

Figure 3. Notothenia is a Coryphaena sister of the deepest oceans.
Figure 4a. Notothenia form the deepest oceans is yet another mahi-mahi descendant in the LRT.
Figure 4b. Notothenia skull.

Notothenia coriiceps
(Richardson 1844; 50cm) is the extant Antarctic yellowbelly rockcod. Added to the LRT six months ago, Notothenia lacks a swim bladder and the bones are dense, accounting for its reduced buoyancy. The body is adapted to sub freezing temperatures. Here it nests with the mahi-mahi, Corphaena and kin, not with traditional perch.

References
Guichenot A 1848. Peces de Chile (In Gay, Claudio. Historia física v política de Chile. Paris & Santiago, 1848). (in Spanish).
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Richardson J 1844. Ichthyology of the voyage of H.M.S. Erebus & Terror. In: Reptiles, fishes, Crustacea, insects, Mollusca, Longman, Brown,London.: 1-16.

wiki/Mahi-mahi – Coryphaena
wiki/Notothenia_coriiceps
wiki/Malacanthus_brevirostris
wiki/Common_dragonet – Callionymus

Revueltosaurus: THE paper finally comes out

Parker et al. 2021 present
the osteology and relationships of Revueltosaurus callendari (Figs. 1–4).

Unfortunately
Parker et al. stick to their original hypothesis, that Revueltosaurus was basal to aetosaurs (heavily armored herbivores, Fig. 6).

Figure 1. Revueltosaurus, early

Here’s the the problem:
The two taxa that eight years ago nested with Revueltosaurus in the large reptile tree (LRT, subset Fig. 5), Tasmaniosaurus and Fugusuchus (Fig. 2) are not mentioned in the Parker et al. text. Neither are the two taxa that nest basal to aetosaurs in the LRT, Ticinosuchus and Hemiprotosuchus (Fig. 6). Why do we not see these four taxa in Parker et al. 2021?

Figure 2. Skulls of Fugusuchus, Revueltosaurus and Tasmaniosaurus compared.

The no. 1 problem in today’s paleontology remains taxon exclusion
This happens over and over again. It’s almost as if paleontology is afraid of discovery. This is ironic because every budding paleontologist wants to discover something. Someone or some system is holding this science back. Even Yale Professor John Ostrom had to wait a few decades for widespread acceptance of a hypothesis (= birds are dinos) he thought was ignored for 100 years when he re-proposed it 50 years ago.

Figure 3. Published diagram of Revueltosaurus skull. Colors added here. Compare to assembled bones in figure 4.

The five small (= 7 to 10 taxa) cladograms published by Parker et al.
(their figure 2) nest the invalid clade ‘Avemetatarsalia‘ (dinosaurs + pterosaurs) with or close to Phytosauria. That doesn’t make any sense, but you see it over and over again. By contrast, phytosaurs do not nest with dinosaurs or pterosaurs when more taxa are added, as documented in the LRT (subset Fig. 5).

Figure 4. Photograph of Revueltosaurus skull from assembled bones. Compare to diagram in figure 3.

Parker et al. concluding remarks
“R. callenderi is a key taxon for clarifying the phylogeny of pseudosuchian archosaurs.”

Their is no clade ‘Pseudosuchia‘ recovered by the LRT (Fig. 5). Let’s fix that. Let’s add taxa to clarify relationships.

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.
Figure 5. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha. Shifting Revueltosaurus to the Aetosauria adds 22 steps to the MPT.

Parker et al. concluding remarks
We have lightheartedly referred to R. callenderi as the “duckbilled platypus” of the Triassic
because of its shared characteristics with aetosaurs such as the laterally oriented squamosal and dorsal and ventral carapace of rectangular osteoderms, its plesiomorphic ilium with a highly reduced preacetabular process, the bulbous fourth trochanter of the femur and unique articulation of the nasal and premaxilla that are only otherwise known in T. dabanensis, the maxillary ridge ventral to the antorbital fossa and interdental plates as in P. kirkpatricki, and of course a tooth morphology and buccal emargination that is convergent with early diverging
ornithischian dinosaurs.

See how these authors glom on to a small set of traits?
Instead they should be recovering a last common ancestor pulled from a wide gamut taxon list. We call trait-mining: Pulling a Larry Martin. Try not to ‘Pull a Larry Martin’. Always find the last common ancestor. Let the software and cladogram tell you how taxa are interrelated, and then which traits they share, not the other way around.

Figure 3. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.
Figure 6. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.

Parker et al. concluding remarks
As a non-aetosaur aetosauriform, R. callenderi is of major phylogenetic significance in determining the early diversification of major clades within Pseudosuchia as aetosauriforms represent a previously unrecognized group of suchian archosaurs that potentially have a wider geographic and temporal distribution.

There is no major phylogenetic significance here.
Rather this is yet another example of academic misdirection. Parker et al. omitted many pertinent taxa documented online for several years (see above). So their long-awaited paper turned out to be flawed by taxon exclusion. They recovered a false positive. Not sure why these PhDs kept their blinders on. Did they know about this omission during manuscript submission and plowed on (= stuck to their guns)? Or were they oblivious? Either way, professionals should be covering all the bases, not leaving it to amateurs to do their work for them. All they had to do was expand their taxon list.

Figure 1. The premaxillae of Ticinosuchus, a stem aetosaur. Note the sharp triangular shape.
Figure 7. The premaxillae of Ticinosuchus, a stem aetosaur. Note the sharp triangular shape.

Historically part of the problem
has been a misinterpretation of the crushed and scattered skull elements of Ticinosuchus (Fig. 7), especially the triangular premaxilla, a trait shared with aetosaurs (Fig. 6) in the LRT (Fig. 5).

References
Parker WG et al. (7 co-authors) 2021. Osteology and relationships of Revueltosaurus callenderi. (Archosauria: Suchia) from the Upper Triassic (Norian) Chinle Formation of Petrified Forest National Park, Arizona, United States. The Anatomical Record Special Issue Article.
DOI: 10.1002/ar.24757

Panguraptor enters the LRT alongside Zuolong

Panguraptor lufengensis
(You et al. 2014; Early Jurassic; LFGT-0103, estimated 2m in length; Figs. 1, 2) was originally considered close to Coelophysis.

Figure 1. Panguraptor skeleton stretched out to an in vivo position based on the in situ drawing by You et al. 2014.
Figure 2. Skull of Panguraptor traced and restored to an invivo position. Note the faint impression of the premaxilla and its teeth in the substrate.

Here
in the large reptile tree (subset Fig. 3) Panguraptor nests closer to larger, Late Jurassic Zuolong (Figs. 4, 5), a taxon not mentioned in the original cladogram. Note the short ribs, tiny forelimbs, tall sacral vertebra, subequal metacarpals.

Figure 3. Subset of the LRT focusing on basal dinosaurs.

Impressions
of the ‘missing’ premaxilla are present (Fig. 2) in situ.

Figure 2. Zuolong skull revised with a backward tilting lacrimal and other minor modifications.
Figure 4. Zuolong skull revised with a backward tilting lacrimal and other minor modifications.
Figure 2. Zuolong skeleton from Choiniere et al.
Figure 5. Zuolong skeleton from Choiniere et al. 2010.

Zuolong sallleei
(Choinere et al. 2010; IVPP V15912; Fig. 1; 3m in length) was originally described as a coelurosaur (related to Ornitholestes) dinosaur from the lower Oxfordian of the Late Jurassic. By contrast, the LRT nests Zuolong at the base of the rarely included Segisaurus/Marasuchus clade, near the base of the Theropoda between Tawa and Sinocalliopteryx. Apparently taxon exclusion was a problem with the original Zuolong results. Choiniere et al. counted 5 sacrals. Perhaps only 4 sacrals were present when compared to the smallish ilium, which has a truncated anterior, like that of fellow clade members.

References
Choiniere JN, Clark JM, Forster CA and Xu X 2010. A basal coelurosaur (Dinosauria: Theropoda) from the Late Jurassic (Oxfordian) of the Shishugou Formation in Wucaiwan, People’s Republic of China. Journal of Vertebrate Paleontology. 30 (6): 1773–1796.
You H-L et al. 2014. The first well-preserved coelophysoid theropod dinosaur form Asia. Zootaxa 3873(3):233–249.

wiki/Zuolong
wiki/Panguraptor

A tiny Triassic theropod pelvis and femur: Pendraig enters the LRT

Spiekman et al. 2021 bring us
their description of a tiny Late Triassic theropod pelvis from Wales, long thought to have been lost until theropod expert and NHM paleontologist, Angela Milner, found it again in the museum. In gratitude the authors named Pendraig milnerae (Figs. 1,2,4,5) after the late professor.

From the abstract
“Our phylogenetic analysis recovers P. milnerae as a non-coelophysid coelophysoid theropod, representing the first named unambiguous theropod from the Triassic of the UK.”

Figure 1. From Spiekman et al. 2021. Substrate removal and DGS colors added here.

Taking a broader view,
in the large reptile tree (LRT, 1953+ taxa; subset Fig. 3) Pendraig (NHMUK PV R 37591; Figs. 1,2,4,5) nests at the base of all theropods other than Tawa (Fig. 5) and the Panguraptor (Fig. 4) clade.

Figure 2. Reconstruction of Pendraig from DGS tracing in figure 1.

An island dwarf?
From the abstract: “Although our results indicate that a reduced body size is autapomorphic for P. milnerae, some other coelophysoid taxa show a similar size reduction, and there is, therefore, ambiguous evidence to indicate that this species was subjected to dwarfism.”

Figure 3. Subset of the LRT focusing on basal dinosaurs.

Rather than dwarfism,
a broader view (Fig. 3) indicates phylogenetic miniaturization (= PM) is at work here. In stepwise fashion Pendraig was smaller than Panguratpor, which was smaller than Tawa (Fig. 4), which was more gracile than Herrerasaurus.

Figure 4. Pendraig and Panguraptor to scale with basal dinosaurs, Herrerasaurus, Tawa and Eodromaeus. This is an example of phylogenetic miniaturization at the genesis of a new clade, an evolutionary process seen often in vertebrates.

Thereafter
Pendraig descendants keep shrinking (Fig. 5) or grow to become giants. It goes both ways, but giants only develop as derived taxa. Small taxa are found continuously at the base of theropod branches. PM typically brings with it some sort of metabolic or reproductive innovation. Here (Fig. 4) lighter, smaller, faster, perhaps more energetic theropods seem to be evolving. Feathers, too.

Figure 5. Pendraig restored based on closely related (Fig. 3) Panguraptor. Scipionyx and Compsognathus to scale.

Spiekman et al. report,
“Our analyses further indicate that, in contrast with averostran-line neotheropods, which increased in body size during the Triassic, coelophysoids underwent a small body size decrease early in their evolution.”

Awkwardly put and incorrect.
After the Triassic there was no “sustained miniaturization from large theropods to smaller birds (also contra Lee, Cau, Naish and Dyke 2014). That study also suffered from taxon exclusion. According to the LRT small theropods the size of Pendraig occupied the bases of all branches that produced large theropods, including large birds (e.g. Gastornis, Struthio, Phorusrhacos).

Spiekman et al. employed an out-of-date cladogram of dinosaur origins
that did not include the other basal archosaurs, bipedal crocodylomorphs. It did not include basal poposaurs. It mistakenly included pterosaur lepidosaurs. As a result, their cladogram does not recover the clade Phytodinosauria among other mishaps.

A little advice for PhDs:
stop borrowing cladograms from other workers, especially flawed cladograms like the one Spiekman et al. borrowed. Make your own cladogram. Start from scratch. Then, and only then, you’ll know it is correct. Then you’ll have the authority of that cladogram to use on all your projects for the rest of your life. It’s not too much work (contra DN). Do your part to keep ‘trust’ out of science: stop borrowing ‘trusted’ cladograms from colleagues.

References
Lee MSY, Cau A, Naish D and Dyke GJ 2014. Sustained miniaturization and anatomicial innovation in the dinosaurian ancestors of birds. Science 345(6196):562–566.
Spiekman SNF, Ezcurra MD, Butler RJ, Fraser NC and Maidment SCR 2021. Pendraig milnerae, a new small-sized coelophysoid theropod from the Late Triassic of Wales. Royal Society Open Science 8:210915. https://doi.org/10.1098/rsos.210915
You H-L et al. 2014. The first well-preserved coelophysoid theropod dinosaur form Asia. Zootaxa 3873(3):233–249.

wiki/Pendraig

Time to reduce the number of orders in bony rayfin fish

The irregular addition of tested taxa has now climbed
well past 100 in the bony rayfin fish subset of the large reptile tree (LRT, 1951+ taxa; Fig. 1). Given that milestone, perhaps now is the time for a reckoning with traditional fish orders. The orders seem to be too numerous, not monophyletic and they don’t nest within one another, as well as they do in the LRT.

Granted, these traditional fish orders were all created piecemeal, over time,
by various, well-meaning systematists prior to the advent of software-assisted phylogenetic analysis programs. Now that things have gotten out of hand, and software is available, perhaps today is a good time for all these many fish orders to be pruned, gathered and reordered in a systematic fashion, as determined by unbiased software, not human-influenced tradition.

I will buy beer for everyone reading this
if this change happens in the next decade. Several workers will have to confirm whatever new topology arises, the definition of consensus.

Figure 1. Subset of the LRT with traditional bony rayfin fish clades colorized. There are far too many named fish orders and they do not form monophyletic nested clades. Second frame proposes simplification of the cladogram into monophyletic clades based on skeletal traits, not genes. Frames change every five seconds.

While clade members of some traditional orders do nest together,
members of the other traditional orders are scattered in a haphazard fashion over the wide gamut of the LRT. Catfish and anchovies aren’t even among these taxa in the LRT (Fig. 1). They nest with lobefins, placoderms, spiny sharks, etc. on the other branch of bony fish.

The following 37 minute YouTube video on fish taxonomy from 2020
follows traditional textbooks and is out-of-date according to the LRT. It omits many pertinent taxa. It seems to be narrated in two different languages, so be ready for that. This video represents the old taxonomy, the one found in textbooks, prior to wide-gamut testing by the LRT (subset Fig. 1).

This second YouTube video from U of California in 2015
is also out-of-date for the same reasons (= following current textbooks). It features Phil Hastings, Scripps Professor, and Curator of the SIO Marine Vertebrate Collection.

The current and traditional ‘overkill’ of fish orders
is a relic of the long history of fish systematics prior to the computer age. Now that we know how to test a wide gamut of fish based on skeletal traits (not genes) using software it’s time to do that. Let’s update the family tree of basal vertebrates with studies that include a taxon list at least as wide ranging as in the LRT (Fig. 1). Later we can add more taxa once the the topology of the tree and its nested clades have been established.

I don’t expect to see changes to textbooks in my lifetime.
Nevertheless, someone has to start the ball rolling. So, let’s do some housekeeping!

The odd and armored cowfish, Lactophrys, enters the LRT

Figure 1. The cowfish, Lactophrys, nests with the queen triggerfish, Balistes, in the LRT.

Lactophrys tricornis
(Swainson 1839, originally Ostracion tricornis Linneaus 1758) is the extant cowfish, a traditional member of the Tetraodontiformes. Here in the LRT it nests with the queen triggerfish, Balistes (below), another traditional member of the Tetraodontiformes. The body is armored. The pelvic fin is reduced to a posterior spine, which is missing in Balistes, despite a very large pelvis (Figs. 3, 4) shaping the ventral torso.

Figure 2. Lactophrys skull from Gregory 1933. Tetrapod homology colors added here. Compare to figure 3.
Figure 3. Skull of the queen triggerfish, Balistes. Compare to figure 2.
Figure 3. The queen triggerfish, Balistes, is related to Mola in the LRT.
Figure 4. The queen triggerfish, Balistes, is related to Lactophrys and Mola in the LRT.

Only about 50 more taxa
are needed until the LRT includes 2000 taxa. Any suggestions for new taxa are welcome.

References
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Swainson W 1839. The natural history of fishes, amphibians and reptiles or monocardian animals. 2 volumes. Longman, Orme, Brown, Green and Longmans, Paternoser Row and John Taylor, Upper Gower Street.

wiki/Lactophrys
wiki/Balistes
wiki/Mola mola

Mammuthus enters the LRT

Today’s entrée was inspired by an excellent PaleoTalks YouTube video
interview of Dr. Grant Zazula, paleontologist from the Yukon Beringia Interpretive Centre. During the course of the online talk, Zazula talks about everything you know and never knew about Ice Age fauna. Chief among them is today’s new taxon.

Mammuthgus primigenius
(Brookes 1828, originally Elephas primigenius Blumenbach 1799; 15,000 years ago; Figs. 1. 3) is the extinct woolly mammoth.

As expected and following tradition,
this new taxon nests with the extant Asian elephant, Elephas (Figs. 2, 4) in the large reptile tree (LRT, 1949+ taxa) with identical scores. No wonder the original description considered the two congeneric.

Figure 1. Skull of Mammuthus. The tusks are much larger in this polar elephant.
FigFigure 2. Skull of Elephas maximus with color overlays. Most of the bones are fused to one another, so this tracing is provisional, pending confirmation and/or better data. Compare to the skull of Procavis (Fig. 3).ure 2. Skull of Elephas maximus with color overlays. Most of the bones are fused to one another, so this tracing is provisional, pending confirmation and/or better data. Compare to the skull of Procavis (Fig. 3).
Figure 2. Skull of Elephas maximus with color overlays. Most of the bones are fused to one another, so this tracing is provisional, pending confirmation and/or better data.

In lateral view the skeletons of Elephas and Mammuthus
(Figs. 3, 4) are nearly identical in morphology. The growth of those heavy tusks required the elevation of the occiput for added muscle and ligament attachment in Mammuthus.

Figure 3. Mammuthus skeleton museum mount. Compare to Elephas in figure 4.

The feet are a little broader in Mammuthus
and the tail is shorter, both in response to the colder climes.

Figure 4. Elephas skeleton. Compare to Mammuthus in figure 3.

References
Blumenback JF 1799. Handbuch der Naturgeshichte, 6th ed xvi, 708pp, Dietrich, Göttingen.
Brookes J 1828. A catalogue of the anatomical & zoological museum of Joshua Brookes. Esq. FRS, FLS ec. Part 1 76 pp. R Taylor, London.

wiki/Mammoth – Mammuthus

Origin of the premaxilla, maxilla, dentary and marginal teeth in vertebrates

Teeth and the cartilage precursors that hold teeth originally appeared in an unknown Silurian shark phylogenetically close to an extant bottom-dwelling shark with a long straight tail (Fig. 1) newly added to the LRT (subset Fig. 5).

The extant zebra shark
(Stegostoma tigrinum, Stegostoma fasciatum Figs. 1–4) nests at the base of all vertebrates with teeth according to the large reptile tree (LRT, 1947+ taxa, Fig. 5).

Figure 1. Stegostoma adults and juveniles.

This taxon also gives us a chance to estimate skull parts
from a simple outline diagram in which ALL of the cranial parts are fused in the only data on the cranium I was able to find (Goto 2001, Fig. 2). Here the topology of processes and apertures permits an estimation of tetrapod homologies. Earlier this method was considered impossible to contentious. Even shark expert, Goto, does not venture to label large areas of the shark skull, only small apertures. Here (Fig. 2) the nares are surrounded by nasals, the brain is surrounded by frontals and parietals, the orbits are bounded posteriorly by a postfrontal, as in tetrapods. Here the palatoquadrate (pq) is re-identified, as before, as the precursor to the lacrimal, the anchor upon which the premaxilla and maxilla are attached as marginal teeth first appear in this taxon.

Figure 2. Stegostoma skull diagram from Goto 2001. Note that Goto labels more apertures than areas. Gray triangles added to show nares. See figure 3 and 4 for premaxilla, maxilla and dentary in anterior view.

Traditionally (according to Wikipedia)
“Teeth are assumed to have evolved either from ectoderm denticles that folded and integrated into the mouth (outside–in theory), or from endoderm pharyngeal teeth (primarily formed in the pharynx of jawless vertebrates) (inside–out theory).”

By contrast, there is no ‘assumed’ in the LRT
where the last common ancestor of all taxa with teeth is Stegostoma (Figs. 1–4). That taxon is a late survivor documenting when and where teeth first appeared in vertebrates. It really is that simple. You don’t have to assume anything if you have a valid cladogram, one that minimizes taxon exclusion.

Prior to adding Stegostoma to the LRT
Ginglymostoma, the closely related nurse shark, was the most primitive taxon with teeth and tooth-bearing structures. Goto 2001 nested Ginglomostoma with Rhincodon, the whale shark and these two nested with Stegostoma based on 136 traits, then again based on mode of reproduction, number of eggs possible in a lifetime and again based on egg case traits. Goto 2001 nested Stegostoma with Rhincodon and these with Ginglymostoma based on 8 soft tissue and tooth traits. So the phylogenetic results of the LRT match those of Goto 2001. That’s confirmation and consensus of the methods employed here. Taxa are more important than characters. Adding taxa makes the LRT more complete. Adding characters does not.

Stegostoma tigrinum
(originally Squalus varius Seba 1758; Forster 1781; 2.5m) is the extant zebra shark. It feeds on small prey hiding in holes and reef crevices. This bottom dweller has a long, straight tail. The zebra shark is oviparous.

Figure 3. Stegostoma premaxilla (yellow) and maxilla (green) producing teeth and distinct from the lacrimal (tan) homolog traditionally labeled the palatoquadrate.
Figure 4. Stegostoma lower jaw with teeth on the dentary homolog arising from the fused articular + angular and surangular homologs.

Fraser et al. 2010 were also interested in the origin of teeth.
From the abstract: “We integrate recent data to shed new light on the thorny controversy of how teeth arose in evolution. Essentially we show (a) how teeth can form equally from any epithelium, be it endoderm, ectoderm or a combination of the two and (b) that the gene expression programs of oral vs. pharyngeal teeth are remarkably similar. Classic theories suggest that (i) skin denticles evolved first and odontode-inductive surface ectoderm merged inside the oral cavity to form teeth (the ‘outside-in’ hypothesis) or that (ii) patterned odontodes evolved first from endoderm deep inside the pharyngeal cavity (the ‘inside-out’ hypothesis). We propose a new perspective that views odontodes as structures sharing a deep molecular homology, united by sets of co-expressed genes defining a competent thickened epithelium and a collaborative neural crest derived ectomesenchyme. Simply put, odontodes develop ‘inside and out,’ wherever and whenever these co-expressed gene sets signal to one another. Our perspective complements the classic theories and highlights an agenda for specific experimental manipulations in model and non-model organisms.”

No phylogenetic analysis appears in Fraser et al. 2010. Stegostoma is not mentioned in the text. Fraser et al. used genes when they should have used a phylogenetic analysis based on traits.

Vaškaninová et al. 2020 sought the origin of teeth in vertebrates.
From the abstract, “The dentitions of extant fishes and land vertebrates vary in both pattern and type of tooth replacement. It has been argued that the common ancestral condition likely resembles the nonmarginal, radially arranged tooth files of arthrodires, an early group of armoured fishes. We used synchrotron microtomography to describe the fossil dentitions of so-called acanthothoracids, the most phylogenetically basal jawed vertebrates with teeth, belonging to the genera Radotina, Kosoraspis, and Tlamaspis (from the Early Devonian of the Czech Republic). Their dentitions differ fundamentally from those of arthrodires; they are marginal, carried by a cheekbone or a series of short dermal bones along the jaw edges, and teeth are added lingually as is the case in many chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). We propose these characteristics as ancestral for all jawed vertebrates.”

According to the LRT, acanthothoracid arthrodires are not the most basal jawed vertebrates with teeth. They are much more highly derived (and degenerate) bony fish. We looked at the Vaškaninová, et al. paper earlier here. It suffers from taxon exclusion.

Figure 5. Subset of the LRT focusing on sharks and kin. Stegostoma is in amber. This is all you have to do to recover the last common ancestor of all vertebrates with marginal teeth.

Take a closer look at the tooth-carrying structures in Stegostoma.
They become granular, no longer joined to one another (except at their common base) at the line where teeth first appear. Like a MC Escher graphic, these grains grow, coalesce and develop cusps to form tooth rows that are maintained posteriorly, like corn rows, as maturation continues.

Forget imaginative hypotheses.
The genesis of teeth in Stegostoma involves the growing and slightly separating granules of the novel tooth-bearing tissues (Fig. 3, 4). Teeth do not appear from the skin or its denticles, nor from the throat or palate. Teeth appear when the premaxilla precursor, the maxilla precursor and the dentary precursor tissues appear. It’s that simple.

You don’t have to always look for fossils.
Sometimes the most primitive member of a clade survives to the present day little changed.

The importance of Stegostoma
to the evolution of marginal teeth in vertebrates has been overlooked by vertebrate paleontologiests and fish experts. If there is a prior mention of this hypothesis, please provide a citation so I can promote it here.

References
Forster JR 1781. Indische Zoologie oder systematische Beschreibungen seltener und unbekannter Thiere aus Indien, mit 15 illuminirten Kupfertafeln erläutert. Nebst einer kurzen vorläufigen Abhandlung über den Umfang von Indien und die Beschaffenheit des Klima, des Bodens und des Meeres daselbst, und einem Anhange, darin ein kurzes Verzeichniss der Thiere in Indien mitgetheilt wird. / Zoologia indica selecta […]. Praemittitur de finibus et indole aeris, soli, marisque indici brevis lucubratio. Seqvitur ad calcem brevis enumeratio animalium Indiae. Gebauer, Halle, 4+iv+42 pp., 15 pls. [German and Latin text; based on Pennant, 1769; second edition in 1795].
Fraser GJ et al. (4 co-authors) 2010. The odontode explosion: The origin of tooth-like structures in vertebrates. Bioessays 32(9): 808–817. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3034446/
Goto T 2001. Comparative Anatomy, Phylogeny and Cladistic Classification of the Order Orectolobiformes (Chondrichthyes, Elasmobranchii). Memoirs of the graduate school of fisheries sciences, Hokkaido University 48(1):1–100.
Vaškaninová V, et al. (6co-authors) 2020. Marginal dentition and multiple dermal jawbones as the ancestral condition of jawed vertebrates. Science, 2020 DOI: 10.1126/science.aaz9431

wiki/Zebra_shark – Stegostoma

Publicity
https://www.sciencedaily.com/releases/2020/07/200709141606.htm

The origin of the spike-tooth in spike-tooth pterosaurs

Apparently this is another traditionally overlooked trait in pterosaurs.
The subject comes back today because it has been getting a lot of hits this week as earlier we looked at the spike tooth in several germanodactylid descendants (Pteranodon, Tapejara, Dsungaripterus).

Here we’ll take a look at other evidence
for anterior premaxillary teeth rotating to point anteriorly and blending to become one spike in two specimens of Germanodactylus (Figs. 1–5) and their ancestors (Fig. 1) The dentary spike tooth is also present at this stage/grade, appearing phylogenetically much earlier in the SMNHS 59395 specimen of Scaphognathus (Fig. 1), not half as tall as the holotype.

Figure 1. Germanodcatylus cristatus and its phylogenetic ancestors back to Scaphognathus. Note the phylogenetic miniaturization during the rotation of the anterior premaxillary teeth. Contra tradition the short rostrum taxa are not juveniles. In this clade going back to Huehuecuetzpalli juveniles have adult proportions and phylogenetic analysis documents this evolution.

Let’s start with the fact
that the pterosaur premaxilla contains a maximum of four teeth. Let me know if you find any exceptions. I’ve studied many (listed in the Large Pterosaur Tree, LPT, 260 taxa) and can find none with more than four teeth. Several derived taxa have fewer, of course.

Figure 2. GIF animation of skull elements (plate and counter plate) with DGS tracings. See figure 3 for reconstruction. Scenes change every 5 seconds. Note the rostral and mandible tip teeth, homologous with those in toothless pterosaurs related to this taxon.
Figure 2. GIF animation of skull elements (plate and counter plate) with DGS tracings. Note the rostral and mandible tip teeth, homologous with those in toothless pterosaurs related to this taxon.
Figure 1. Germanodactylus cristatus, specimen B St 1892 IV 1 (n61 in Wellnhofer's 1970 catalog focusing on the two anterior precursors to the premaxillary spike tooth and single dentary spike. Figure 1. Germanodactylus cristatus, specimen B St 1892 IV 1 (n61 in Wellnhofer's 1970 catalog focusing on the two anterior precursors to the premaxillary spike tooth and single dentary spike.
Figure 3. Germanodactylus cristatus, specimen B St 1892 IV 1 (n61 in Wellnhofer’s 1970 catalog focusing on the two anterior precursors to the premaxillary spike tooth and single dentary spike.

The transition to ‘toothless’ pterosaurs
begins here, with Germanodactylus in the Late Jurassic Solnhofen Formation. Here (Figs 3, 4) the anterior two premaxillary teeth rotate anteriorly, forming a harder beak tip. Ultimately the two teeth merge to form one cylindrical spike (Fig. 4).

Figure 2. Skull of the SMNK-PAL 6592 Germanodactylus focusing on the precursor to the premaxillary spike tooth and dentary spike tooth. Figure 2. Skull of the SMNK-PAL 6592 Germanodactylus focusing on the precursor to the premaxillary spike tooth and dentary spike tooth.
Figure 4. Skull of the SMNK-PAL 6592 Germanodactylus focusing on the precursor to the premaxillary spike tooth and dentary spike tooth.

Also overlooked by pterosaur workers
is the transition from germanodactylids to pteranodontids (Fig. 5), a topic we looked at earlier here. Most workers follow Unwin 2003 and Kellner 2003 nesting Pteranodon with toothy ornithocheirids. Unfortunately taxon exclusion mars these and other pterosaur cladograms.

Matching YPM 1179 to the post-crania of SMU 76476 (Myers 2010) and overprinted with SMNK PAL 6592. The resemblance is indeed remarkable.
Figure 5. Matching YPM 1179 to the post-crania of SMU 76476 (Myers 2010) and overprinted with SMNK PAL 6592. The resemblance is indeed remarkable other than size and teeth.
Figure 6. Pteranodon occidentalis to scale with the SMNK PAL 6592 specimen of Germanodactylus.
Figure 6. Pteranodon occidentalis to scale with the SMNK PAL 6592 specimen of Germanodactylus. The Pteranodon skull is larger and the teeth are missing.

References

reptileevolution.com large pterosaur tree