Updating and inverting Gregory 1933: Pre-shark skulls and the ontogenetic disappearance of teeth

From Gregory 1933:
“The typical fish skull, or syncranium (Fig. 1), notwithstanding the intricacy of its details, is generally recognized to be composed of two sharply contrasting divisions, which may be called the neurocranium, or braincase, and the branchiocranium.”

The neurocranium nests the brain, eyes, pineal and balancing organs.

The branchiocranium includes the gill arches and the mouth parts, which are derived from gill arches.

Some workers include a dermocrarnium, derived from the dermis. That would include the nasals and circumorbitals, not shown in Gregory’s figure (Fig. 1).

Figure 1. Syncranium of a bony fish from Gregory 1933, here with colors added.
Figure 1. Syncranium of a bony fish from Gregory 1933, here with colors added.

From Gregory 1933:
“The subdivision of the skull into separate bones has been conditioned chiefly by the necessities of growth and nutrition and that originally the endocranium was a continuum and the dermocranium consisted of a shell of ectosteal tissue, covering the chief functional regions or organs. Even now after the separate bones have enjoyed many millions of years of individuality, they are primarily regional subdivisions of functionally organic groups or tracts as well as organs in themselves.”

“In nearly all the hosts of typical fishes the syncranium is concerned with the pursuit and capture of living prey, the exceptions being few and peculiar forms such as the parrotfishes and the like, which have given up this freely competitive roving life and become highly specialized for living either on aquatic vegetation or on sessile animals.”

The LRT recovers a different pattern. The earliest ‘fish’ (like Arandaspis) were actually armored lancelets, filtering food in large branchial chambers, rather than pursuing prey. Transitional lancelet-fish, like Birkenia, retained a ventrally open oral cavity, still ventral in osteostracans and sturgeons.

In sturgeons the nasal bone or cartilage becomes an electrosensory organ to detect buried prey. When discovered prey is sucked in with an extensible tube. This is the first step toward feeding on larger prey. That arrangement reappears ventrally in later skates and rays and anteriorly in perch, frogfish, etc.

Figure 1. Chondrosteus animation (2 frames) in situ and reconstructed in lateral view. This is the transitional taxon linking sturgeons to bony fish + sharks.
Figure 2. Chondrosteus animation (2 frames) in situ and reconstructed in lateral view. This is the transitional taxon linking sturgeons to bony fish + sharks.

This tube evolves by neotony to become toothless jaws in Chondrosteus, (Fig. 2) basalmost sharks and manta rays that continue filter-feeding in open waters.

When tiny teeth appear in the paddlefish, Polyodon, larger prey is still not pursued. perhaps because only Polyodon larvae (Fig. 3) have teeth. Adults (Fig. 4) loose teeth. I just learned (from Sewertzoff 1928) that Acipenser (a sturgeon, Fig. 6) larvae also have tiny teeth (Fig. 5). Just like growing paddlefish, these tiny teeth also reduce and disappear as this sturgeon matures.

Figure 2. Polyodon hatchling prior to the development of the long rostrum with maturity.
Figure 3. Polyodon hatchling prior to the development of the long rostrum with maturity.
Figure 4. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.
Figure 4. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.
Figure 5. Medial section of Acipenser larva with temporary teeth from Sewertzoff 1928.
Figure 5. Medial section of Acipenser larva with temporary teeth from Sewertzoff 1928. Not sure if the yolk sac is absorbed before of after teeth appear.
Figure 1. Acipenser, a sturgeon.
Figure 6. Acipenser, a sturgeon.

From Gregory 1933:
“The profound researches of Stensio (1927) and Kiser (1924) have left no reasonable doubt however, that one or another of the ostracoderms gave rise to the modern class of cyclostomes, including the lampreys and hags, thus confirming the earlier views of Cope and others.”

Just the opposite, according to the LRT.

“The ancient ostracoderms, or pre-fishes, are first known from a single plate found in rocks of Middle Ordovician (Harding) age.”

This gives time for poorly ossified sturgeons, paddlefish, sharks and basal bony fish to appear and evolve during the fossil-poor Silurian making way for derived placoderms, like Entelognathus to appear in the Late Silurian.

“The true or gnathostome fishes are not known until the Devonian period and even up to the present time there are no known forms which definitely connect them with the ostracoderms.” 

That was in 1933. Now we have bony fish, like a mislabeled catfish, an osteoglossimorph Sinacanthus , a few lobefins like Guiyu and Psarolepis, and the derived placoderm Entelognathus, in the Silurian. Poorly ossified sturgeons are proximal descendants of ostracoderms in the LRT.

From Gregory 1933:
“As a class the ostracoderms are so inferior to the gnathostomes in their locomotor apparatus that they have even been assumed to be a specialized bottom-living group with no claim to be considered in the line of ascent to the gnathostomes. That was partly because it was further assumed that the continuous “headshield” must always be the result of the fusion of small polygonal plates. But Stensio’s intensive researches have revealed that the primitive ostracoderm shield was supported by a continuous endoskeleton without sutures, which was covered by a bony membrane.”

Sturgeons still have that head shield supported by a continuous endoskeleton without sutures. When sturgeons appeared, the splanchocranium began to separate once again from the neurocranium, as in Birkenia and the thelodonts. This was yet another reversal.

“According to the evidence adduced by Stensio (1925, pp. 160-164; 187-189) it appears that the cartilaginous condition of the skull in modern elasmobranchs is not improbably a result of degeneration, as in the better known cases of the cartilaginous skulls of sturgeons, spoonbills, Ceratodus [a lungfish], salmon, etc. Thus even the exoskeleton of modern sharks is retrogressive and now represented only by the skin and shagreen armor.”

Just the opposite, according to the LRT.

From Gregory 1933:
“Neither the Catopteridae
[no longer used, but refers to releatives of certain paleoniscid bony fish] nor any other known family of Chondrostei [= polyphyletic in the LRT, but traditionally includes sturgeons, paddlefish, bichirs and several extinct clades] however, appear to be directly ancestral to the typical holostean or protospondylous ganoids and later teleosts.”

Just the opposite, according to the LRT, which nests sturgeons, basal to paddlefish, basal to sharks, basal to all bony fish and tetrapods.

Figure x. Shark skull evolution.

From Gregory 1933:
“Stensio also concludes that the saurichthyids, like the sturgeons, palseoniscids, coelancanthids, dipnoans and arthrodires, form a degenerative series. By this he means especially that in such series the adult endocranium is better ossified, less cartilaginous, in the earlier than in the later members of the series.”

The LRT does not score for “better ossified” but relies more on shapes and proportions of scored elements.

“The sturgeon has specialized in the opposite direction from that of the primitive chondrosteans, as it has acquired an excessively small suctorial mouth which is withdrawn far behind the projecting rostrum.”

Just the opposite. The sturgeon mouth is primitive in the LRT.

[In sturgeons] “The whole snou tand fore part of the braincase is warped downward above the capacious orobranchial cavity in order to bring the snout down parallel to the ground.”

Just the opposite. This is the primitive condition, as seen in osteostracoderms.

From Gregory 1933:
“The rostral barbels are specialized tactile organs,”

Not specialized, but primitive, homologous with the buccal cirri of lancelets in which barbels/cirri serve both a chemoreceptive and mechanorerceptive role.

Figure 8. Extant lancelet (genus: Amphioxus) in cross section and lateral view. The gill basket nearly fills an atrium, which intakes water + food, sends the food into the intestine and expels the rest of the water.

From Gregory 1933:
“The neurocranium of the sturgeon and spoonbill are largely cartilaginous but with more or less extensive centers of ossification. It has been assumed by Watson and Stensio that this partly cartilaginous condition is due to retrogressive development (perhaps to the retention of early larval conditions in the adult). Sewertzoff, however, as a result of his embryological investigations (1928) challenges this view and concludes that the recent chondrosteans are much more nearly related to the elasmobranchs than was formerly suspected and that in many respects they are more primitive than the Palaeozoic palasoniscids. He holds among other things that the numerous ossicles in the snout of the sturgeons are more primitive than the few rostral elements of the palaeoniscids.”

“After a careful consideration of these opposing evidences and interpretations, I can only record my impression that the older view is by far the more probable, and that for many reasons, only a few of which may here be noticed.”

The LRT agrees with Sewertzoff 1928, not with Gregory 1933.

“Whatever may be said as to the sturgeon, it can hardly be doubted that the exoskeleton of the spoonbill {Polyodon) is in a highly retrogressive condition. In place of the fully formed ganoid scales of its palaeozoic relatives it has a practically naked body with a few vestigial horny scales in the upper lobe of its heterocercal fin.”

Just the oppositive. The spoonbill (= paddlefish) is primitive and basal to sharks.

Figure 2. Subset of the LRT focusing on one clade of bony fish that includes lobefins, but not exclusively.
Figure 9. Subset of the LRT focusing on one clade of bony fish that includes lobefins, but not exclusively.

From Gregory 1933:
“Moreover, many of the peculiar characters of the sturgeons are foreshadowed by theJurassic Chondrosteus (Fig. 195), which on the other hand retains features that are clearly inherited from a palseoniscoid stock, as well noted by A. S. Woodward (1895, p. viii). Watson (1925, p. 831) has already shown the annectant character of the Chondrosteidse between the palaeoniscids and the sturgeons.”

Just the opposite. In the LRT Chondrosteus is neotonously derived from sturgeons, basal to sharks. Compare the sturgeon larva (Fig.5) to the adult Chondrosteus, (Fig. 1). On the other hand, palaeoniscids, are no longer considered a natural group.


References
Gregory WK 1933. Fish skulls. A study of the evolution of natural mechanisms. American Philosophical Society 23(2) 1–481.
Sewertzoff AN 1928. The head skeleton and muscles of Acipenser ruthenus. Acta Zool., 9:193–319, 9 pis.

Overlooked reversals in vertebrate evolution

Some of the following reversals were covered in earlier posts. 
Others premiere here. Still others remain overlooked or forgotten for the moment. Come back over time to see additions as they spring to mind.

Reversals are distinct from convergent traits
in that reversals also appear in ancestral taxa (in the LRT) while convergent traits do not.

  1. Platypus electrosensory bill — sturgeon, paddlefish, shark electrosensory rostrum
  2. Odontocete simple cone teeth — basal bony fish through pelycosaur simple cone teeth
  3. Multituberculate reappearance of post-dentary bones — cynodont jaw joint
  4. Prohalecites gill cover (operculum) — sturgeon, paddlefish, ratfish gill cover
  5. Minjinia, a disc-head, jawless placoderm — drepanaspid jawless anapsid
  6. Echinosorex, the moonrat and member of Glires lacks gnawing incisors — tree shrews that are not members of Glires also lack gnawing incisors
  7. Fins (dorsal, pectoral, pelvic, caudal) in ichthyosaurs, odontocetes, mysticetes, and other tetrapods — Similar fins in basal tetrapods (= fish)
  8. Loss of hind limbs in snakes, whales, amphisbaenids — lampreys, Birkenia
  9. Acanthostega radius twice as long as the ulna — as in pre-tetrapod lobefin fish
  10. Ossified skin (bony plates) in ankylosaurs, glyptodonts, etc. — Ossified scales in basal vertebrates (= fish)
  11. Flightless birds — flightless pre-bird theropods
  12. Loss of a flexible neck in mysticetes — basal vertebrates and tetrapods
  13. Heterodont dentition in Longisquama + pterosaurs and, by convergence in cynodonts —as in Hybodus, a shark basal to bony fish
  14. New world vulture overall morphology (pigeon sisters) — Old world vultures (hawk sisters)
  15. Long-legged shore birds (stilts, Himantopus, derived from short-legged Eocypselus) — long-legged basal birds like seriemas (Cariama).
  16. Atavistic tails in humans — monkeys, lemurs
  17. Extensible ventral mouth parts in skates — as in pre-gnathostome sturgeons
  18. Gill openings ventral to pectoral fins in skates and rays — as in osteostracans
  19. Separation of the gill basket from the neurocranium in sturgeons — as in Birkenia
  20. Fusion of the gill basket with the neurocranium in osteostracoderms — as in Arandaspis.
  21. Extended rostrum in pachycormiforms — as in Chondrosteus and sharks.

Figure 1. Skulls of pterosaur ancestors from Huehuecuetzpalli through Macrocnemus, Cosesaurus, Longisquama and the pterosaur Bergamodactylus.

Figure 1. Skulls of pterosaur ancestors from Huehuecuetzpalli through Macrocnemus, Cosesaurus, Longisquama and the pterosaur Bergamodactylus. Note the heterodont dentition (#13). These taxa were omitted from the recent pterosaur precursor paper by Ezcurra et al. 2020, by Hone and Benton 2007, 2008 and every other cladogram (Kellner 2003, Unwin 2003) over the last twenty years.

Prohalecites: the new tiny ancestor of all bony ray fin fish

Updated February 10 2021
with a some details modified in the morphology resulting in a shifting of this taxon to the base of the ray-fin fish clade (not the spiney/lobe-fin fish clade).

…and it still looks like Hybodus,
(Fig. 2) its 50x larger proximal ancestor.

A nice surprise today
as a phylogenetically miniaturized hybodontid shark with gill covers and ray fins, Prohalecites porroi (Figs. 1, 4, 5, Belloti 1857, Deecke 1889, Tintori 1990, MCSNIO P 348, Middle Triassic; 4cm), enters the large reptile tree (LRT, 1780+ taxa) as THE basalmost bony ray-fin fish. 

Figure 1. Prohalecites porroi in situ from Arratia 2015, colors added. No dorsal spines here.

Figure 1. Prohalecites porroi in situ from Arratia 2015, colors added. No dorsal spines here.

That makes Prohalecites close to a late-surviving
human, mammal, reptile, tetrapod and bony fish ancestor. Prohalecites needs to be in every paleo textbook from here on out.

No trace of scales is preserved
in any specimen. No neurocranial material is preserved. Hemichordacentra are present. The preoperular is so slender it is twig-like.

Figure 2. Hybodus fraasi fossil in situ is 50x larger than an adult Prohalecites, the basalmost bony fish.

Figure 2. Hybodus fraasi fossil in situ is 50x larger than an adult Prohalecites, the basalmost bony fish.

Surprisingly little has been written
about Prohalecites. While Arratia 2015 considered it “the oldest of the Teleosti”, she did not mention Hybodus, its proximal ancestor in the LRT.

Tintori 1990 left Prohalecites as a Neopterygian incertae sedis,
“because its characters do not perfectly fit in any of these cited groups.” 

Arratia and Tintori 1998 wrote, 
“Prohalecites possesses an interesting mosaic of primitive and advanced chalacters, some of which have been previously interpreted as synapomorphies of Teleostei.” 

“The election of the outgloup plays a significant role in the phylogenic position of Prohalecites and other neopterygians. Unquestionably, Prohalecites is not a Teleostei.”

Their cladograms nested Prohalecites between Amia and all higher bony fish. Neither sharks nor Hybodus are mentioned in the text. So taxon exclusion hampers an otherwise highly focused study.

Figure 1. Subset of the LRT focusing on ray-fin fish, their speed, niches and extant.

Figure 1. Subset of the LRT focusing on ray-fin fish, their speed, niches and extant.

Once again,
too much focus, not enough of a wide-angle view hampered prior workers. Whenever taxa are tested together that have never been tested together before, new relationships can be recovered. That’s why the LRT was created 10 years ago. You should have so many taxa in your cladogram that it tells you which taxa to include in your more focused study. Cherry-picking taxa has become outdated. That traditional practice leads to false positives and enigmas.

Figure 4. Prohalecites skull from Arratia 2015, colors added.

Figure 4. Prohalecites skull from Arratia 2015, colors added.

Arratia 2015,
wrote on the history and current status of the fish clade Teleostei (Müller 1845).

Figure 3. Prohalecites diagram from Tintori 1990, colors added.

Figure 5. Prohalecites diagram from Tintori 1990, colors added.

According to Arratia,
Müller defined the clade based on soft tissue traits not visible in fossils. Thus, the taxon content of the clade has changed several times over the last century.

From the Arratia abstract:
“The monophyly of the total group Teleostei, which now includes Triassic pholidophorids, is supported by numerous synapomorphies.” This, of course, would be “Pulling a Larry Martin“, which happens frequently out there. Remember, it is better to define a clade by establishing two taxa that recover a last common ancestor on a wide gamut, comprehensive cladogram. Don’t rely on a few or a few dozen traits. Convergence must be allowed in your hypothetical model, because convergence and reversal did happen.

Arratia also wrote,
“Prohalecites from the Ladinian/Carnian (Triassic; c. 240 Ma) boundary represents the oldest stem teleost.” That piqued my interest in this tiny fish only half as long as a human finger.

According to Arratia, 
“during most of the last 170 years there has been a dichotomy in the treatment of teleosts, where fossil and living groups have been studied separately, including distinct classifications.”

Looking at the simple cladogram in figure 5 of Arratia 2015,
it looks like Teleostei includes Pholidophorus, Leptolepis, their last common ancestor and all descendants. Two other cladograms are shown in Arratia figure 8 based on earlier analyses. A full page cladogram is shown in Arratia figure 9 placing Amia and Lepisosteus as two of five outgroup taxa. Basal ingroup taxa include Pachycormus and Aspidorhynchus. Synapomorphies were listed for each node followed by a report on the pertinent traits. All this was for nought because the phylogenetic context was incomplete and invalid.

Arratia concludes, 
“The results demonstrate the importance of including fossil teleosts in the phylogenetic analysis, especially because some of their characters and combination of characters introduce a new perspective in understanding the origin and early radiation of the group, and indirectly provide a new scenario to interpret homologous characters.”

It goes without saying that Arratia 2015 did not include
placoderms, or lobefins in a teleost clade defined by Pachycormus and Aspidorhynchus in the LRT.

Prohalecites demonstrates, once again,
phylogenetic miniaturization at the genesis of a major clade, despite its late (Middle Triassic) appearance in the fossil record.

Was Prohalecites larger in the Silurian?
Maybe. It’s worth looking for. Or maybe bony fish began by neotony.

Earlier we looked at the origin of bone ‘islands’
on a cartilage substrate in the hatchlings and juveniles of the extant taxon, Amia. Prohalecites documents the origin of bone in the tiny adult bony fish descendants of hybodont sharks.


References
Arratia G and Tintori A 1999. The caudal skeleton of the Triassic actinopterygian †Prohalecites and its phylogenetic position, p. 121–142. In: Mesozoic Fishes 2—Systematics and Fossil Record. G. Arratia and H.-P. Schultze (eds.). Verlag Dr. F. Pfeil, München.
Arratia G 2015. Complexities of early Teleostei and the evolution of particular morphological structures through time. Copeia 103(4):999–1025.
Bellotti C 1857. Descizione di alcune nuove specie di pesci fossili di Perledo e di altre localtta lombarde. 419–432. In Sopani A (ed) Studi geologici sulla Lomabardia. Editore Turati, Milano.
Deecke W 1889. Über Fischea ùs verschiedenen Horizonten der Trias. Palaeontogaphica 45:97–138.
Müller J 1845. Über den Bau und die Grenzen der Ganoiden, und über das natürliche System der Fische. Physikalisch-Mathematische Abhandlungen der ko¨niglichen Akademie der Wissenschaften zu Berlin 1845:117–216.
Tintori A 1990. The actinopterygian fish Prohalecites from the Triassic of northern Italy. Palaeontology 33:155–174.

 

wiki/Prohalecites
wiki/Teleostei

The origin of European eels and the origin of four-eyed fish

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

Today the extant topminnow,
Fundulus (Figs. 1), nests in ‘the Right Side’ of the Osteichyes, the clade that includes only ray fins (Fig. 2). The more taxa, the better cladodgram. Earlier errors are here corrected by the addition of taxa and data, some of which provide views not available earlier. Such work is still rewarding.

Figure 3. The four-eyed fish, Anableps, from three data sources. Compare to Fundulus in figure 4.

Figure 1. Skull of Fundulus from Gregory 1938.  Note the jugal (cyan blue). Compare to the barracuda, Sphyraena, in figure 2. 

Figure 2. Skull of the barracuda, Sphyraena. Compare to the killifish, Fundulus, in figure 1.

Figure 2. Skull of the barracuda, Sphyraena. Compare to the killifish, Fundulus, in figure 1.

Adding characters would never have resolved this issue.
Only adding taxa can do so, contra what so many PhDs say. Not sure why. It didn’t make sense in 2012 and it still doesn’t make sense in 2020. More characters are not needed. More taxa smooth out all the rough edges, illustrating the microevolution that ultimately creates macroevolution.

Part 2.
An overlooked European eel ancestor,
Bavarichthys (Arratia and Tischliner 2010; Late Jurassic) is here identified.

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

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

Bavarichthys incognitus
(Arratia and Tischlinger 2020; Late Jurassic) was originally considered a member of the “Crossognathiforms with a large head about 30% in standard length and a characteristically elongate snout, more than 25% in head length. In the LRT it nests between the extant anchovy, Elops and the extant European eel, Anguilla.

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

Figure 6. Skull of Anguilla, the European eel, compares well with that of Bavarichthys. Note the loss and reduction of preorbital bones.

Protanguilla palau 
(Johnson et al. 2011; 18cm; Fig. 7) is a newly discovered ‘living fossil” transitional taxon from Bavarichthys to Anguilla. Distinct from eels, Protanguilla has gill rakers, fewer than 90 vertebrae, pterotic does not approach anterior margin of pterosphenoid, and the latter bone participates in the posterior margin of the orbit. Eels are traditionally associate with Elops. These new taxa fill in the gaps.

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

Figure 7. Protanguilla is a recently discovered short eel, transitional from Bavarichthys in the LRT.

The nesting of Bavarichthys
basal to Protanguilla and Anguilla appears to be a novel hypothesis of interrelationships. Let me know if there is an earlier citation so I can promote it.


References
Arratia G and Tischlinger H 2010. The first record of Late Jurassic crossognathiform fishes from Europe and their phylogenetic importance for teleostean phylogeny. Fossil Record 13(2):317-341.
Johnson GD, Ida H, Sakaue J, Sado T, Asahida T and Miya M 2012. A ‘living fossil’ eel (Anguilliformes: Protanguillidae, fam nov) from an undersea cave in Palau. Proceedings of the Royal Society. (in press): 934–943. doi:10.1098/rspb.2011.1289

denmark/scientists-solve-the-riddle-of-eel-evolution/1420760
wiki/Killisfish – Fundulus
wiki/Pupfish
wiki/Anableps

wiki/Protanguilla

Traditional fish cladograms and skull bones

López-Arbarello and Sferco 2018
provide a traditional cladogram (Fig. 1) of the Neopterygii (= new-ray fin fish) (= “the dominant group of fishes.) 

From the abstract:
“The phylogenetic relationships of the recently described genus †Ticinolepis from the Middle Triassic of the Monte San Giorgio are explored through cladistic analyses of the so far largest morphological dataset for fossil actinopterygians, including representatives of the crown-neopterygian clades Halecomorphi, Ginglymodi and Teleostei, and merging the characters from previously published systematic studies together with newly proposed characters. †Ticinolepis is retrieved as the most basal Ginglymodi and our results support the monophyly of Teleostei and Holostei, as well as Halecomorphi and Ginglymodi within the latter clade.”

  1. Teleostei96% of all extant species of fish.
  2. Holostei – extant gars and bowfins + extinct kin
  3. Halecomorphi – extant bowfins (Amia) only + extinct kin
  4. Ginglymodi – extant gars (Lepisosteus) only +  extinct kin

Earlier the LRT nested
Ticinolepis crassidens with Perleidus, Tarrasius and Annaichthys, apart from Ticinolepis longaeva, which nests at the base of lobefin fish with coelacanths, like Latimeria.

Figure 1. Cladogram from Lopez-Arbarello and srenco

Figure 1. Cladogram from Lopez-Arbarello and Sferco 2018. Gray tone added. Open boxes are taxa in the LRT. Yellow boxes are new taxa in the LRT. Compare to figure 2.

The López-Arbarello and Sferco 2018 cladogram does not match
the fish portion of the large reptile tree (LRT, 1778+ taxa; subset Fig. 2) due to a wider gamut of taxa in the LRT that attracts various fish outside of their too inclusive clade (Fig. 1). Their outgroup taxon, Pteronisculus, is a derived taxon in the Palaeonisciformes in the LRT. Both cladograms nest Boreosomus close to Pteronisculus.

Figure 2. Subset of the LRT focusing on one clade of bony fish that includes lobefins, but not exclusively.

Figure 2. Subset of the LRT focusing on one clade of bony fish that includes lobefins, but not exclusively.

Scheenstia is added to the LRT
(Figs, 2, 3). This large Late Jurassic ganoid-scaled fish is a good example of what happens when fish bones develop over a cartilaginous template in hatchlings. Here (Fig. 3) several bones have tetrapod homolog names. Others do not. The colors indicate which contiguous small bones are homologs of tetrapod bones, as if they were fused together.

Figure 3. Scheenstia diagram from Lopez-Arborello and Sfenco 2018. Colors added here to show tetrapod homologs. Gray tone overprints bones that need tetrapod homologs. Others already have them.

Figure 3. Scheenstia diagram from Lopez-Arborello and Sfenco 2018. Colors added here to show tetrapod homologs. Gray tone overprints bones that need tetrapod homologs. Others already have them. This is how bony fish are scored in the LRT.

It takes a lot of related fish
to see which bone plates belong to others. It’s all about identifying patterns and exceptions and it is easy to make mistakes since this is a pioneering hypothesis. Earlier we looked at the immature skull of the extant bowfin, Amia, which has similar bone ‘islands’ that often, but not always fuse to form larger facial bones in the adult.

Sometimes a wider view from an outsider
not trained in traditional fish morphology is needed to shed light on simplifying and unifying skull nomenclature across all chordate clades. This probably won’t happen in my lifetime, but it needs to be done. You can see (Fig. 1) what happens whenever the focus is too narrow. It will be okay to have a narrow focus again AFTER a wider understanding of clades becomes more universal. That’s why the LRT is here, to take that first step.


References
López-Arbarello A and Sferco E 2018. Neopterygian phylogeny: the merger assay. Royal Society open science 5: 172337. http://dx.doi.org/10.1098/rsos.172337

https://en.wikipedia.org/wiki/Neopterygii

Pterosaur tooth scratches and diets

Bestwick et al. 2020 wrote:
“Pterosaurs, the first vertebrates to evolve active flight, lived between 210 and 66 million years ago. They were important components of Mesozoic ecosystems, and reconstructing pterosaur diets is vital for understanding their origins, their roles within Mesozoic food webs and the impact of other flying vertebrates (i.e. birds) on their evolution.

Vital? Is that what they call ‘hyperbole?’ For their outgroup, the authors employ the basal bipedal crocodylomorph with tiny hands and no toe 5, Scleromochlus, so… so far tooth scratches are not proving ‘vital for understanding their origins.‘ They ignored citations, scratches and common sense. Not a good start.

“However, pterosaur dietary hypotheses are poorly constrained as most rely on morphological-functional analogies. Here we constrain the diets of 17 pterosaur genera by applying dental micro wear texture analysis to the three-dimensional sub-micrometre scale tooth textures that formed during food consumption. We reveal broad patterns of dietary diversity (e.g. Dimorphodon as a vertebrate consumer; Austriadactylus as a consumer of ‘hard’ invertebrates) and direct evidence of sympatric niche partitioning (Rhamphorhynchus as a piscivore; Pterodactylus as a generalist invertebrate consumer).

That’s refreshing! Delivering results in an abstract. Unfortunately, there’s nothing new here and Nature papers usually break new ground.

“We propose that the ancestral pterosaur diet was dominated by invertebrates and later pterosaurs evolved into piscivores and carnivores, shifts that might reflect ecological displacements due to pterosaur-bird competition.”

Again, nothing new here.

The authors downplay fossilized stomach contents 
due to their limited preservation, so they put greater emphasis on the scratched enamel of pterosaur teeth. Comparisons are made to extant reptile tooth scratches from crocs and monitor lizards. Iguanids are not mentioned. The word ‘arboreal’ is likewise not found in the text.

Figure 3. Dsungaripterus single teeth at the tips of the jaws. Phylogenetically these began with Germanodactylus (Fig. 4).

Figure 1. Dsungaripterus single teeth at the tips of the jaws. Phylogenetically these began with Germanodactylus (Fig. 4).

Those tooth scratches are rather indistinct.
Odd that the authors downplay stomach contents in pterosaurs (based on their rarity) given the headline of their paper. So-called toothless pterosaurs are ignored despite the fact that the tips of beaks are teeth (Fig. 1). Oddly, so are dsungaripterids (Fig. 1) and ctenochasmatids, both of which have marginal teeth.

Pterodaustro adult with manual digit 3 repaired.

Figure 2. Pterodaustro adult with manual digit 3 repaired.

Juvenile diets are not mentioned appropriately
Rather phylogenetically miniaturized adult basal Rhamphorhynchus specimens are considered juveniles, forgetting the fact that all pterosaurs mature isometrically, as demonstrated by Pterodaustro (Fig. 2) and Zhejiangopterus ontogenetic series. We also have one juvenile Rhamphorhynchus, identical to larger adult.


References
Bestwick J, Unwin DM, Butler RJ and Purnell MA 2020. Dietary diversity and evolution of the earliest flying vertebrates revealed by dental micro wear texture analysis. Nature Communications https://doi.org/10.1038/s41467-020-19022-2

Bestwick J, Unwin DM, Butler RJ, Henderson DM and Purnell MA 2018. Pterosaur dietary hypotheses: a review of ideas and approaches. Biological Reviews https://doi.org/10.1111/brv.12431

Ubirajara jubatus: Shoulder rods? Or long skinny leg bones?

Smyth et al. 2020
brings us a new, articulated, partial, crushed skeleton of a small Aptian (Early Cretaceouse) compsognathid theropod with interesting soft tissue. The authors compared the integumentary structures of Ubirajara jubatus to those of the standard wing bird-of-paradise. A reconstruction (Fig. 1) shows four “stiff rod-like structures projecting from its shoulders,” according to Karina Shah, writing for NewScieintist.com.

We’ve never seen anything like this,
which makes it newsy. But is it real?

This taxon will not go into the LRT
because too little is known of the skeleton (Figs, 2, 3).

Figure 1. Ubirajara illustration showing proposed four "stiff rod-like structures projecting from its shoulders."

Figure 1. Ubirajara illustration showing proposed four “stiff rod-like structures projecting from its shoulders.”

The specimen reconstruction (above) was restored
from a plate and counter plate (Fig. 2) with bones at the periphery and a big glob in the middle.

Figure 2. Plate and counter plate image and tracing from Smyth et al. 2020. The tracings were combined by Smyth et al. here in figure 3.

Figure 2. Plate and counter plate image and tracing from Smyth et al. 2020. The tracings were combined by Smyth et al. here in figure 3. Sorry for the low resolution. This is just for display.

Fortunately, Smyth et al. provided a combined tracing
(Fig. 3). Note both legs are missing.

Or are they?
Instead Smyth et al. identify two pairs of straight 15 cm rods, which you can see in their illustration above (Fig. 1). Their diagram shows BMFIs directed outside the blob, aiming toward the top of the scapula.

Occam’s Razor suggests
those paired rods emanating from the shoulders may instead be long, straight legs, knees flexing near the shoulders, splitting posteriorly as shown on the overlays (Fig. 3) toward an absent pelvis for the femur and an absent foot for the tibia. This alternate restoration is a guess based on the scant evidence shown here and an aversion to completely new structures.  But somebody has to say it, just to open this discussion. If I’m wrong, I’m wrong.

Figure 3. From Smyth et al. 2020 with overlays suggesting the possibility that the paired rods growing from the shoulders may instead just be legs with knees near the shoulders. Just a hypothesis awaiting confirmation or refutation. Here the vertebrae are also renumbered.

Figure 3. From Smyth et al. 2020 with overlays suggesting the possibility that the paired rods growing from the shoulders may instead just be legs with knees near the shoulders. Just a hypothesis awaiting confirmation or refutation. Here the vertebrae are also renumbered and the hand is reconstructed.

Anyone can make a mistake.
Even if there are four co-authors. We’ve seen this sort of thing before in Yi qi and Ambopteryx where the authors mistook a displaced ulna or radius for a novel bone, their styliform. The important thing is to not perpetuate the myth of an entirely new structure, if it is a myth. This Ubirajara example is not so clear (based on indistinct impressions) so I could be wrong. Let’s figure this out. This is the loyal opposition talking, building on the tenth man rule (from World War Z).

Figure 4. Ubirajara rough reconstruction from diagram in Smyth et al. 2020.

Figure 4. Ubirajara rough reconstruction from diagram in Smyth et al. 2020 (Fig. 3).

Has anyone else
come up with this novel hypothesis? Let me know if this leg idea can be readily refuted.


References
Smyth RSH, Martill DM, Frey E Rivera-Silva HE and Lenz N 2020. A maned theropod dinosaur from Brazil with elaborate integumentary structures. Cretaceous Research. doi:10.1016/j.cretres.2020.104686

wiki/Ubirajara_jubatus

Rhinochimaera is added to the LRT as another ratfish

Adding taxa continues to clarify hypothetical interrelationships
among all included taxa in the LRT. especially in the shark grade/clade where skull elements are cartilaginous and tend to fuse together leaving fewer clues/landmarks in the more derived taxa.

Didier 1995 reports,
“There are two hypotheses on the origin of Holocephali (Bonaparte 1832). The first and most generally accepted scenario is that holocephalans have evolved from some lineage of bradyodont sharks. The second hypothesis suggests that holocephalans are most closely related to placoderms.”

In the LRT placoderms are not basal to sharks, but nest with bony fish in a clade that reverted to a cartilaginous internal skeleton while keeping a bony dermal skeleton. So the second hypothesis is falsified.

According to Wikipedia, “Most Bradyodonti fossils consist of jaws and teeth. These indicate that Bradyodonti ate mollusks and other shelled invertebrates. Their bodies were probably broad and flattened, like modern rays.”Bradyodonti” can also refer to the present-day Chimaera or ratfish of the order Chimaeriformes, which have an upper jaw fused to the braincase and a flap of skin covering the gill slits.”

So, once again suprageneric taxon labels leave us all a little confused since Bradyodonti = Chimaeriformes in some circles.

Figure 4. Shark skull evolution according to the LRT. Compare to figure 1.

By adding taxa
to the large reptile tree (LRT, 1776 taxa, subset Figs. 1, 2) holocephali (= chimaera, ratfish) arise from taxa near Squalus and Heterodontus (Fig. 8) close to the shark/ray split where marginal teeth become like paving stones.

By adding colors to skulls,
fused and obscure elements may be identified with tetrapod homologs. That makes scoring and identifying errors easier.

Earlier we looked at
a dorsal view of the skull of the dogfish shark, Squalus (Fig. 1) here. You’ll note that there is much more fusion in the skull cartilage of ratfsh (Figs. 5–7) including the fusion of the lacrimal complex (= traditional palatoquadrate) with the neurocranium and dermocranium.

Figure 6. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.
Figure 6. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.

Didier 1995 reports,
“The adductor muscles of Heterodontus also lie anterior to the eye and superficially they resemble chimaeroid fishes in this respect. I interpret this as a convergent feature of heterodontids and chimaeroids.” That is the only mention of Heterodontus (Fig. 1) in the text. Squalus is the outgroup taxon in Didier’s figure 46 cladogram (Fig. 3).

Figure 1. Cladogram from Didier 1995, colors added to reflect taxon inclusion, exclusion according to the LRT (see figure 2).
Figure 3. Cladogram from Didier 1995, colors added to reflect taxon inclusion, exclusion according to the LRT (see figure 2).

Getting back to Rhinochimaera
(Fig. 4–6). It should come as no surprise that, with its long rubbery snout, Rhinochimaera is among the most derived chimaeras in the LRT (subset Fig. 2). That proboscis is supported by a single slender nasal cartilage articulating on a joint with the rest of the smaller, underlying nasal cartilages (Fig. 6), homologs with similar, smaller elements in Callorhinchus (Fig. 7).

Figure 1. The long-nosed chimaera (Rhinochimaera africana?).
Figure 4. The long-nosed chimaera (Rhinochimaera africana?).
Figure 5. Fused cartilage skull of Rhinochimaera lacking the tactile/sensory probe supports. Compare to diagram in figure 6.
Figure 5. Fused cartilage skull of Rhinochimaera lacking the tactile/sensory probe supports. Compare to diagram in figure 6.
Figure 6. Diagram of Rhinochimaera pacifica from Didier 1995. Inverted area and colors added to show interpretations of element boundaries based on Callorhinchus (Fig. 7) and other related taxa.
Figure 6. Diagram of Rhinochimaera pacifica from Didier 1995. Inverted area and colors added to show interpretations of element boundaries based on Callorhinchus (Fig. 7) and other related taxa.

Rhinochimaera nests with
Callorhinchus (Fig. 6) in the LRT (subset Fig 2), The latter helps identify elements in the former (Figs. 5, 6). Note the lateral rostral rods (l. rost. rod) arises from the lacrimal. The medial rostral rod (m. rost. rod) arises from the nasal.

Figure 7. Callorhinchus milii skull in several views. All the cartilage is fused here, so color identifies elements. Note the tactile rostral elements are smaller and not associated with the premaxilla (contra Didier 1995).
Figure 7. Callorhinchus milii skull in several views. All the cartilage is fused here, so color identifies elements. Note the tactile rostral elements are smaller and not associated with the premaxilla (contra Didier 1995).

Heterodontus
(Fig. 8) likewise helps identify skull elements in chimaeroids prior to the fusion of the lacrimal complex (= traditional palatoquadrate) with the dermocranium and neurocranium.

Figure 8. Heterodontus skull with colors added to identify elements as tetrapod homologs.
Figure 8. Heterodontus skull with colors added to identify elements as tetrapod homologs.

Every added taxon
helps clarify the position of every nested taxon as every included taxon affects every other. Likewise, all included and tested taxa help identify fused elements whenever they appear in taxa like Rhinochimaera (Figs. 4–6). Earlier guesses have been repaired. Current guesses will be repaired as soon as errors are discovered. Sutures may not be visible, but the jaw joint is still the quadrate. The large strut above it is still the hyomandibula. The nasal still extends over the nares. Etc. etc.

Some say I need to look at specimens firsthand.
There’s an answer to that. Although I have examined many specimens firsthand, that’s not my job at present. Precision observations will come, but first a wide-angle view of hundreds of taxa is what is required, because 1) specialists, by definition, are not going to look outside their speciality, and 2) no one has done this before. This one time, just let one guy on the planet do this and the rest of the specialists can benefit from whatever insights are recovered here in this wide-angle view of many taxa at once, the LRT.


References
Bonaparte CL 1832. Iconografia delle fauna italica per le quattro classi degli animali vertebrati. Tomo III. Pesci. Roma. [Issued in puntata (installments), without pagination; total of 556 pp., 78 pls.
Didier DA 1995. 
Phylogenetic Systematics of Extant Chimaeroid Fishes (Holocephali, Chimaeroidei). American Museum Novitates 3119:86pp.
Lund R 1977. New information on the evolution of the bradyodont chondrichthyes. Fieldiana 33(28)521–538.
Venkatesh B et al. 2014. Elephant shark genome provides unique insights into gnathostome evolution. Nature 505:174–179.

Basal bony fish descendants of hybodontid sharks

Moving on from sharks in general,
hybodontid sharks (Fig. 1)  have the most heavily ossified skulls… without a rostrum… with jaws extending to the anterior margin, as in bony fish.

For those following reader comments
on the latest heresy, reader comments do not refer to ALL the skull bones only the dermatocranium. Keep this in mind when reading the following from the U. West Vancouver labs online study of skulls accessible here.

The neurocranium (= chondrocranium) surrounds the brain and certain sense organs (parietal, postparietal, intertemporal, supratemporal, tabular and all occipital bones). In sharks the neurocranium is composed of cartilage, but in most other vertebrates the cartilage is replaced by bone.

The splanchnocranium consists of the gill arches and their derivatives… part cartilage, part endochondral bone. The splanchnocranium evolved to become the bones of the human face (below the frontals, sans nasals = maxilla + premaxilla + lacrimal + jugal + quadrate + dentary + ear bones (= former hyomandibular + jaw bones)) and the face of Amia the bowfin (Figs. 1, 2). The preopercular disappears in basal tetrapods no longer breathing with gills.

The dermatocranium consists of the original dermal scales (= armor) of ostracoderms and sturgeons. The authors say “The dermatocranium forms most of the skull,” but really all that is left over from the above lists are the nasals, frontals and circumorbitals (= prefrontals, postfrontals, postorbitals). The squamosal and quadratojugal appear later as cheek bones split in two, then split again. And also do so by convergence in unrelated taxa. So what are we arguing about with regard to shark-bony fish homologies? Not many bones after all.

Figure 1. Fish evolution from Hybodus to Amia documenting the shark to bony fish transition.
Figure 1. Fish evolution from Hybodus to Amia documenting the shark to bony fish transition.

Keys to understanding this issue include:

  1. The elements of the dermocranium in shark outgroup taxa (sturgeon and paddlefish)  = bone sheath over cartilage.
  2. The elements of the dermocranium in sharks  = prismatic cartilage, more ossified in hybodonts
  3. The elements of the dermocranium in proximal shark descendants (Amia and the moray eel, Gymnothorax, Fig. 1) = bone redevelops surrounding sensory cells over a cartilage bauplan (Fig. 3).
Figure 4. Skull of the extant bowfin (Amia). Compare to figure 3.
Figure 2. Skull of the extant bowfin (Amia). Compare to figure 3.

As a quick review, Bemis et al. 1997 report, 
“the bones more or less closely ensheath the underlying endochondral rostrum” of sturgeons and paddlefish. Sharks lack this sheath of bone.

As reported earlier, Pehrson 1940 examined
a series of embryonic stages of Amia calva (Fig. 3). Pehrson was a fan of naming fish bones in accord with those of pre-tetrapods, as he reports, “There seems to be no doubt that the intertemporal and supratemporal parts of the developing composite bone correspond to the similarly named bones in Osteolepidae and Rhizodontidae.” Thus Pehrson labels the intertemporal and supratemporal. Perhaps he was the first. I repeated the experiment and came to the same conclusions in sharks. Note the reduction of the long nasals in bony fish precursors, the hybodontid sharks.

Figure x. Embryo development in the bowfin, Amia. The facial bones develop as buds surrounding dermal sensory organs 'floating' on top of a cartilage base.
Figure 3. Embryo development in the bowfin, Amia. The facial bones develop as buds surrounding dermal sensory organs ‘floating’ on top of a cartilage (chondral) and prechondral base.

Some anterior Hybodus teeth start to look like Amia teeth (Fig. 4).
Blazejowski 2004  reported, “Gradual height reduction of the principal cusp is observed in successive tooth rows: the lateral teeth have low, long crowns with characteristic large lingual process, sometimes less pronounced as a buttress. Root is strongly ad−
joined to the crown in every tooth.”

Figure 4. Teeth of Hybodus species from Blazejowski B 2004, colors added. Note the wide variety and how two specimens approach the narrow cone morphology found in the basal bony fish, Amia and Gymnothorax (Fig. 1).
Figure 4. Teeth of Hybodus species from Blazejowski B 2004, colors added. Note the wide variety and how two specimens approach the narrow cone morphology found in the basal bony fish, Amia and Gymnothorax (Fig. 1). Blazejowski reported, “Gradual height reduction of the principal cusp is observed in successive tooth rows: the lateral teeth have low, long crowns with characteristic large lingual process, sometimes less pronounced as a buttress. Root is strongly ad− joined to the crown in every tooth.”

Pehrson 1940 reports:
“Three different stages of the formation of the premaxillary are shown. The anterior, dental part of the bone is clearly distinguishable from the posterior and dorsal part, situated above the cartilage.” Pehrson also describes the appearance of ossification where prior cartilage has dissolved, convergent with the process of fossilization.

Figure x. Shark skull evolution.

On the other hand… What taxa came before sharks?
Phylogenetically, that is (Fig. 5). Answer: Paddliefish. Chondrosteus. Sturgeons. Osteostraci. Birkenia (Fig. 5) in that order. All are bottom feeders with a ventral mouth, like the ventral mouth of basal sharks, like the goblin ‘shark’, now nesting with paddlefish in the LRT.

According to Bemis et al.
“We discuss five features fundamental to the biology of acipenseriforms [= sturgeons + paddlefish] that benefit from the availability of our new phylogenetic hypothesis:

  1. “specializations of jaws and operculum relevant to jaw protrusion, feeding, and ram ventilation;” (Chondrosteus, the goblin shark (Mitsukurina, and other basal sharks also protrude the jaws)
  2. “anadromy or potamodromy and demersal spawning;” (anadromy = migration of fish, from salt water to fresh water, as adults; potamodromy = freshwater fish; demersal spawning = mouth brooding)
  3. “paedomorphosis and evolution of the group;” (= retention of juvenile or larval traits in adulthood. Note the resemblance of larval paddlefish to basal sharks, Fig. 5).
  4. “the biogeography of Asian and North American polyodontids and scaphirhynchines;
  5. “the great abundance of electroreceptive organs in the rostral and opercular regions.” (e.g. sturgeons + paddlefish vs. sawfish, goblin sharks, hammerheads, etc).

According to Wikipedia,
Notable characteristics of Acipenseriformes include:

  1. Cartilaginous endoskeleton – as in sharks and fish more primitive than sharks
  2. Lack of vertebral centrum – as in fish more primitive than sharks
  3. Spiral valve intestine – as in sharks, bichirs, gars and lungfish, the last two by reversals.
  4. Conus arteriosus = infundibulum, a conical pouch found in the heart from which the pulmonary trunk artery arises. (not scored in the LRT, which looks at bones and their homologs).

Bemis et al. report,
“Acipenseriforms are central to historical ideas about the classification and evolution of fishes.”

Indeed. The LRT comes to the same conclusion.

“Acipenseriforms also are noteworthy because of their unusual mixture of characters, which caused early debate about their classification.”

Ray fins + armor + cartilage skeleton + ventral oral cavity + lack of jaws are some of these mixed characters. Actually, these are just primitive, something that has been overlooked until the LRT added taxa to recover a new family tree topology.

“Two aspects of living Acipenseriformes were especially problematic for early ichthyologists: (1) reduced ossification of the endoskeleton combined with presence of an extensive dermal skeleton; and (2) the presence of a hyostylic jaw suspension and protrusible palatoquadrate recalling the jaws of sharks.”

This is going to piss off ichthyologists: The palatoquadrate is not a palatine and only a small portion is a quadrate. The palatoquadrate is largely homologous to the lacrimal with fusion of the preopercular in some taxa. On taxa with teeth we find the fusion of the premaxilla and maxilla (tooth-bearing elements) to the much larger lacrimal. The former and future jugal are also involved.

“The current conventional view (developed and refined by many authors… holds that Acipenseriformes evolved from a ‘paleonisciform’ ancestor via paedomorphic reduction of the skeleton and specialization of the feeding system, but there is much more to the history of ideas about the systematics of this group.”

The current conventional view is incorrect according to the LRT, which tests a wider gamut of fish and nests traditional asipenseriformes basal to unarmored sharks, derived from armored osteostracoderms (Fig. 5). There was no paedomorphic reduction of the skeleton. Instead, sturgeons were basal to the origin of the jaws and skeleton.

Bemis et al. reviewed the history of sturgeon taxonomy, 
reporting: “Throughout this period [Linneaus 1788 through Heckel 1836]. most workers adhered to the classical idea that sturgeons must be closely related to sharks because they appeared to share a largely cartilaginous endoskeleton and similar jaw suspension. Chondrosteus, was named by Agassiz (1844) and described by Egerton (1858). Müller (1846) defined three grades of bony fishes — Chondrostei, Holostei and Teleostei — on the basis of increasing degrees of ossification. In doing this, Müller rejected the classical idea that sturgeons are closely related to sharks and accepted them as osteichthyans. Sewertzoff (1925, 1926b, 1928) was the only 20th century ichthyologist to seriously consider a closer link between sturgeons and chondrichthyans. Sewertzoff (1925) presented his conclusions as a phylogenetic tree, in which chondrosteans are shown as the sister group of all other bony fishes, and emphasized the presence of a protrusible palatoquadrate in both elasmobranchs and sturgeons. We now regard palatoquadrate protrusion as derived independently within chondrosteans (see additional discussion in the final section of this paper). Norris (1925) and others noted neuroanatomical similarities between sturgeons and sharks, but these are almost certainly plesiomorphic features (see Northcutt & Bemis 1993), and few workers ever accepted Sewertzoff’s view (see Berg 1948b and Yakovlev 1977 for additional history and critique).”

“It was not until later, when Gardiner (1984b) published the first generic level cladogram including fossil and recent Acipenseriforms, that interest in their phylogenetic interrelationships began to grow. Gardiner’s (1984b) analysis was controversial because he suggested that paddlefishes were diphyletic,

“From this brief history [much abbreviated above], it is clear that phylogenetic studies of Acipenseriformes are still in their infancy.”

This is only due to taxon exclusion and traditional bias (= textbooks). Including more taxa without bias (Fig. 5) as in the LRT, clarifies phylogenetic studies.

Figure 4. Paddlefish (Polyodon) hatchling in 2 views. This taxon marks the origin of marginal teeth. Barbels go back to whale sharks (Fig. 5). From the caption: Scanning electron micrographs of Polyodon spatula larva: The olfactory pit has not yet completely subdivided into anterior and posterior nares. Many clusters of ampullary electroreceptors are visible on the cheek region dorsal to the upper jaw. The teeth of the upper jaw are erupting in two series. Additional erupting teeth can be seen at the leading edge of infrapharyngobranchial.
Figure 6. Paddlefish (Polyodon) hatchling in 2 views. This taxon marks the origin of marginal teeth. Barbels go back to whale sharks (Fig. 5). From the caption: Scanning electron micrographs of Polyodon spatula larva: The olfactory pit has not yet completely subdivided into anterior and posterior nares. Many clusters of ampullary electroreceptors are visible on the cheek region dorsal to the upper jaw. The teeth of the upper jaw are erupting in two series. Additional erupting teeth can be seen at the leading edge of infrapharyngobranchial.

Sturgeon-like barbels (not those of catfish, carp, hagfish or zebrafish)
originate with sturgeons and continue in paddlefish (Fig. 6). Whale sharks retain barbels (Fig. 7), but they tuck them away into the corners of their mouth. Manta rays (Fig. 8) lose their barbels. Sawsharks keep theirs. Not sure yet about the Mandarin dogfish.

Figure 7. Whale shark (Rhincodon) mouth. Note the lack of marginal teeth, presence of barbels and single nares.
Figure 7. Whale shark (Rhincodon) mouth. Note the lack of marginal teeth, presence of barbels extending the mouth corners  and single nares.
Figure 8. Manta ray mouth lacking a barbel. Compare to its living sister, Rhynchodon, the whale shark.
Figure 8. Manta ray mouth lacking a barbel. Compare to its living sister, Rhynchodon, the whale shark. Cephalic lobes are anterior extensions of the pectoral fins.

The nesting of sturgeons and paddlefish 
primitiive to sharks appears to be a novel hypothesis of interrelationships recovered by the LRT simply by adding taxa. In like fashion, the nesting of moray eels and bowfins arising early from sharks also appears to be a novel hypothesis of interrelationships. If there is a prior citation to either, please let me know so I can promote it.


References
Bemis WE, Findeis EK and Grande L 1997. An overview of Acipenseriformes. Environmental Biology of Fishes 48: 25–71, 1997.
Blazejowski B 2004. Shark teeth from the Lower Triassic of Spitsbergen and their histology. Polish Polar Research 25(2)153–167.
Maisey JG 1983. Cranial anatomy of Hybodus basanus Egerton from the Lower Cretaceous of England. American Museum Novitates 2758:1–64.
Maisey JG 1987. Cranial Anatomy of the Lower Jurassic Shark Hybodus reticulatus
(Chondrichthyes: Elasmobranchii), with Comments on Hybodontid Systematics. American Museum Novitates 2878: 1–39.
Pehrson T 1940. The development of dermal bones in the skull of Amia calva. Acta Zoologica 21:1–50.

Splanchnocranium

https://en.wikipedia.org/wiki/Acipenseriformes

https://www.zoology.ubc.ca/~millen/vertebrate/Bio204_Labs/Lab_3__Skull.html

Overlooked convergence: sharks and whales have a gelatinous snout

Short one today.
The pictures tell the story.

Everyone knows
the snout of the sperm whale is shaped by large sacs of spongy gelatinous material, the spermaceti organ and the melon (Fig. 1).

Figure 1. Sperm whale head diagram showing  the spermaceti organ and the junk (melon) sitting atop the elongate rostrum, as in sharks, more or less.  See figure 2.

Figure 1. Sperm whale head diagram showing the spermaceti organ and the junk (melon) sitting atop the elongate rostrum, as in sharks, more or less. See figure 2.

Shark skulls are not shaped like hydrodynamic bullets.
like the skulls of sturgeons, paddlefish and bony fish. Rather, shark skulls (Fig. 2), like sperm whale skulls, have gelatins that fill the voids and support their bullet-shaped snouts.  Since I didn’t see anything like this when I ‘googled’ it, I thought to add it to mix.

Figure 2. Skull of the dogfish shark, Squalus, superimposed on a graphic of the invivo shark. Yellow areas added to show the extent of the gelatinous material that fills the empty spaces above and below the cartilaginous rostrum (nasal homolog).

Figure 2. Skull of the dogfish shark, Squalus, superimposed on a graphic of the invivo shark. Yellow areas added to show the extent of the gelatinous material that fills the empty spaces above and below the cartilaginous rostrum (nasal homolog).

Yesterday’s post on shark skull cartilage
and the bony homologs one can clearly see by coloring the elements (the now common DGS method) invited a reader’s comments that what I’m doing ‘is the death of science.’ As longtime readers know, I follow the evidence and point out flaws in traditional hypotheses, including instances of taxon omission. That this is necessary points not to the death of science, but to the willingness of someone to test untested hypotheses and taxon lists.

I welcome evidence to the contrary.
I make changes constantly. I follow the evidence, not the textbooks and not the professors, unless the evidence supports them.

Thank you
for your interest in this ongoing online experiment of a life-long learner and heretic.