Proteus, the blind cave salamander, enters the LRT

Losing its maxilla
(Fig. 1) did not stop this taxon from sporting a lot of other teeth in the palatine, ectopterygoid and maybe the vomer, even though only the premaxillary teeth line up with dentary teeth.

Figure 1. Skull of Proteus the white olm. Colors added. Note the lack of a lacrimal and maxilla.

Figure 1. Skull of Proteus the white olm. Colors added. Note the lack of a lacrimal and maxilla.

 Proteus the white olm
(Figs. 1, 2), is a blind cave salamander with a long torso, tiny limbs and external gills (Fig. 2).

Figure 2. Skeleton of Proteus, the white olm.

Figure 2. Skeleton of Proteus, the white olm.

Proteus anguinus
(Laurenti 1768) nests with Necturus, the mudpuppy. The lacrimal and maxilla are absent. The postorbital and postfrontal are stretched out. External gills enable Proteus to remain underwater. Apparently the dorsal portion of the vertebral column is very short (about 5 vertebrae), with the majority comprised of lumbar vertebrae (without dorsal ribs).


References
Laurenti JN 1768. Synopsin Reptilium. J.T. de Trattnern, Viennae, pp. 35–36.

wiki/Olm

From Tapanila et al. 2020: Edestus, a scissors ‘shark’, enters the LRT

Among the oddest fish in the late Paleozoic seas,
are relatives of Helicoprion, famous for its buzz saw teeth (Fig. 3) that grew in a single spiral set in the mid-line of the jaws. Unfortunately not enough is known of the skull to attempt a nesting in the large reptile tree (LRT, 1812+ taxa) at present.

Figure x. Shark skull evolution diagram.

Earlier
Harpagofututor (Figs. 2, 3), a Carboniferous relative of today’s moray eel (Gymnothorax), was tentatively allied with the buzz-saw clade because it shared a small medial tooth row.

Today
Edestus heinrichi (Leidy 1856; Fig. 1; FMNH PF2204; 25cm skull length; Pennsylvanian) joins this clade with its scissors-like medial jaws (Fig. 1) and enough skull to work with.

Figure 1. Skull of Edestus from Tapanila et al. 2018 and reconstructed here using DGS methods.

From the Tapanila et al. 2020 abstract
“Sharks of Late Paleozoic oceans evolved unique dentitions for catching and eating soft bodied prey. A diverse but poorly preserved clade, edestoids are noted for developing biting teeth at the midline of their jaws. Helicoprion has a continuously growing root to accommodate >100 crowns that spiraled on top of one another to form a symphyseal whorl supported and laterally braced within the lower jaw. Reconstruction of jaw mechanics shows that individual serrated crowns grasped, sliced, and pulled prey items into the esophagus.”

Figure 2. Harpagofututor skull colored and reconstructed here. Compare to Gymnothorax in figure 4.
Figure 2. Harpagofututor skull colored and reconstructed here. Compare to Edestus in figure 1

From the abstract, continued.
“A new description and interpretation of Edestus provides insight into the anatomy and functional morphology of another specialized edestoid. Edestus has opposing curved blades of teeth that are segmented and shed with growth of the animal. Set on a long jaw the lower blade closes with a posterior motion, effectively slicing prey across multiple opposing serrated crowns.

Figure 5. Harpagofututor male and female skulls. Added here is the best partial skull of the buzz tooth shark, Helicoprion.
Figure 3. Harpagofututor male and female skulls. Added here is the best partial skull of the buzz tooth shark, Helicoprion.

Tradtionally
Edestus and Helicoprion are portrayed with a shark-like body, but phylogenetic bracketing gives it a moray eel-type body (Fig. 5), like Harpagofututor.

Figure 4. From Tapanila et al. 2020, animated here to show the biting cycle of Edestes.
Figure 4. From Tapanila et al. 2020, animated here to show the biting cycle of Edestus.

From the abstract, continued:
“The symphyseal dentition in edestoids is associated with a rigid jaw suspension and may have arisen in response to an increase in pelagic cephalopod prey during the Late Paleozoic.”

Note that Gymnothorax, the extant moray eel (Fig. 6), also has large palatal teeth along the symphysis (= midline) by homology.

Figure 1. Harpagofututor female from Lund 1982.
Figure 5. Harpagofututor female from Lund 1982.
Figure 2. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.
Figure 6. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.

Pulling prey deeper into the jaws
is a trait shared with the moray eel (Gymnothorax, Fig. 6), though done with an extra set of esophageal jaws (Fig. 7), distinct from the buzz-saw and scissors sharks.

Figure 7. GIF animation showing the dual bite of the dual jaws in moray eels. Both are derived from gill bars.
Figure 7. GIF animation showing the dual bite of the dual jaws in moray eels. Both are derived from gill bars.

Special thanks to reader JeholornisPrima
who sent a link to the Tapanila et al. 2020 paper on Edestus this morning to get this ball rolling.


References
Leidy J 1856. Indications of five species, with two new genera, of extinct fishes. Proc Acad Nat Sci Philadelphia 7:414.
Tapanila L, Priuitt J, Wilga CD and Pradel A 2020. Saws, Scissors, and Sharks: Late Paleozoic Experimentation with Symphyseal Dentition. The Anatomical Record 303:363–376. https://doi.org/10.1002/ar.24046

wiki/Edestus

Priacodon: How to tell a crown mammal from a mammal mimic

Jäger et al. 2020 discuss ‘molar’ occlusion
in a tiny taxon, Priacodon fruitaensis (LACM 120451, Fig. 1), they said was a crown mammal (a clade with living relatives). Priacodon is principally represented by a mandible with teeth and a maxilla with teeth. Triconodont ‘molar’ cusps are three in number and aligned like a row of three knives distinct from basal cynodonts and basal mammals.

Figure 1. Priacodon µCT scans from Jäger et al. 2020. Colors and restoration added. This looks like a mammal jaw. The LRT nests it with mammal mimics. That's an odd sort of canine with more than one cusp.

Figure 1. Priacodon µCT scans from Jäger et al. 2020. Colors and restoration added. This looks like a mammal jaw. The LRT nests it with mammal mimics. That’s an odd sort of canine with more than one cusp.

The authors wrote: 
“Triconodontids are a clade of the eutriconodontans which is a clade of early crown mammals with a fossil record from the Late Jurassic through the Late Cretaceous.”

So this clade had plenty of time to develop their unique teeth and convergent jaw joints alongside crown mammals (= monotremes + marsupials + placentals).

By contrast 
the large reptile tree (LRT, 1786+ taxa, subset Fig. 4) nested Priacodon and kin like Sinocodon (Fig. 2), within a clade of mammal mimics arising from the cynodont,  Pachygenelus, and preceding the Last Common Ancestor of all living mammals, Megazostrodon (Fig. 5). That LCA status makes Megazostrodon the most primitive of crown mammals. Any taxa preceding Megazostrodon are excluded from crown mammals. A valid cladogram is needed to place taxa within a crown clade or outside it. Jäger et al. did not provide a cladogram.

Wang et al. 2001 provided a traditional cladogram of mammals and pre-mammals. That was invalidated in 2016 by the addition of taxa to the LRT.

The single replacement of milk teeth with adult teeth
also marks Megazostrodon as a mammal because toothless hatchlings are initially feeding on their mother’s mammary glands, but that’s beside the point. That’s a trait, not a phylogenetic nesting  node.

Figure 1. Sinoconodon growth series including jaws and teeth, here colorized from Zhang et al. 1992.

Figure 2. Sinoconodon growth series including jaws and teeth, here colorized from Zhang et al. 1992. Note the lack of tiny post-dentary bones in this mammal-mimic.

Unfortunately,
this is a continuing problem in mammal paleontology going back before Repenomamus (Fig. 3), an Early Cretaceous mammal-mimic, typically considered the largest mammal in the Cretaceous. According to Wikipedia, “Repenomamus is a genus of triconodonts, a group of early mammals with no modern relatives.” According to the LRT, they have no living relatives because they are pre-mammals or mammal-mimic cynodonts.

Tiny post-dentary bones
This is a classic case of “Pulling a Larry Martin” because both Repenomamus and Priacodon have a certain trait shared with mammals by convergence. They lack the small post-dentary bones thought to be lost only in mammals. As a result they also have a dentary-squamosal jaw joint. The authors put all their money on this single trait and did not recognize the possibility of convergence. They didn’t provide a phylogenetic analysis that included all pertinent taxa.

In counterpoint, 
Megazostrodon (Fig. 5) retains tiny post-dentary bones. These ultimately migrate to help form the middle ear bones of higher mammals.

A few years ago
I had a chat with co-author R Cifelli in Oklahoma with regard to the nesting of multituberculates in Glires in the LRT. Multis redevelop tiny post-dentary bones by reversal according to the LRT, which tests a suite of 235 traits from head to tail. Cifelli wasn’t ready to consider non-traditional solutions based on an expanded taxon list and the possibility of a reversal.

Figure 4. Repenomamus reconstructed using DGS methods. The manus and feet are loose figments at present. Despite its predatory nature, note the reduction in canines, a clade trait.

Figure 3. Repenomamus reconstructed using DGS methods. The manus and feet are loose figments at present. Despite its predatory nature, note the reduction in canines, a clade trait.

Relatives of Sinoconodon replace their teeth multiple times,
(Fig. 2) as in cynodonts and reptiles in general. But even if they had single tooth replacement, their nesting on the LRT apart from crown mammals indicates they are not crown mammals, but mammal-mimics. Like Repenomamus (Fig. 3) and Priacodon (Fig. 1), Sinoconodon also lacked tiny post-dentary bones and had a dentary-squamosal jaw joint.

In their conclusion, the Jäger et al. note:
“Triconodontidae exhibit a molar series that is unique among mammals and is not directly comparable to any extant counterpart.” That’s because triconodonts are not related to extant counterparts, aka: crown mammals. These esteemed authors “Pulled a Larry Martin” by putting a few traits ahead of a suite of hundreds of traits in a phylogenetic analysis.

Convergence runs rampant in the LRT.
The LRT weeds out convergence. That’s why you need to run your own analysis and expand your own taxon list. Don’t rely on a few traditional traits.

Figure 2. Subset of the LRT highlighting the anomodontia and dicynodontia closer to the origin of the Therapsida.

Figure 4. Subset of the LRT from 2019 focusing on the Therapsida. Red taxa were tested separately due to too few characters known for a permanent place in the LRT.

Whatever Jäger et al. discovered
by closely examining the occlusal pattern in Priacodon, their study was hobbled by their invalid assignment of Priacodon to the clade crown Mammalia. Despite years in this profession, they had no idea that triconodonts were mammal mimics. To avoid problems like this, get a wide-angle view before setting up your microscopic views.

Figure 1. Megazostrodon skull in several views. Drawings from Gow 1986. Colors applied here.

Figure 5. Megazostrodon skull in several views. Drawings from Gow 1986. Colors applied here.

Taxon exclusion continues to be the number one problem in paleontology,
as you can see dozens of times if you click here: keyword: taxon+exclusion.


References
Jäger KRK, Cifelli RC and Martin T 2020. Molar occlusion and jaw roll in early
crown mammals. Scientific Reports (2020) 10:22378 https://doi.org/10.1038/s41598-020-79159-4
Wang Y-Q, Hu Y-M, Meng J and Li C-K 2001. An ossified Meckel’s cartilage in two Cretaceous mammals and origin of the mammalian middle ear. Science 294:357–361.

wiki/Crown_group
wiki/Repenomamus
wiki/Priacodon

What do larval sturgeons eat (when they have teeth)?

Today more evolutionary gaps are filled
and gaffs are rectified as novel hypotheses of interrelationships between sturgeons and sharks are further cemented with more data. When all the parts keep falling into place like this, a hypothesis is more likely to be correct.

Yesterday I learned
that larval sturgeons (like larval paddlefish) have small sharp teeth. These are lost when hatchlings grow more than 3cm in length. At this point their diet changes from open water microscopic copepods to river bottom macroscopic arthropods. At the same time their mouth parts become extensible vacuum cleaner tubes, usually carried inside, sometimes everted (Fig. 2b).

Figure x. Medial section of Acipenser larva with temporary teeth from Sewertzoff 1928.
Figure 1. Medial section of Acipenser larva with temporary teeth from Sewertzoff 1928. Looks more like a shark than a sturgeon here because this is where sharks come from in the LRT.

Zarri and Palkovacs 2018 described
larval green sturgeon diets. “Fish smaller than 30 mm had teeth on the oral jaws and showed a strong reliance on zooplankton prey. The developmental loss of teeth in fish greater than 30 mm was associated with decreased zooplankton consumption and increased richness of benthic macroinvertebrates in diets.”

Figure 2. Growth stages in Acipenser transmontanus, a species of white sturgeon.
Figure 2. Growth stages in Acipenser transmontanus, a species of white sturgeon. First the yolk sac is absorbed, then external feeding begins. Adult armor is derived from ostracoderm armor.

According to the online The Fish Report
“The study found that the most common larval sturgeon prey included copepods (a kind of tiny zooplankton), and macroinvertebrates such as mayflies, midges, and blackflies. The scientists also noted an interesting diet shift: larval sturgeon consumed zooplankton and macroinvertebrates in roughly equal amounts until they grew to 30 millimeters in total length, at which point their macroinvertebrate consumption increased. This shift coincided with the young sturgeon losing their teeth (fun fact: unlike humans, sturgeon start out life with teeth and lose them as they grow older).”

Zooplankton prey
include copepods (a kind of tiny zooplankton) that floats freely in open waters.

Benthic macroinvertebrates
such as larval mayflies, midges, and blackflies that live in river sands and muds.

Figure 5. Sturgeon mouth animated from images in Bemis et al. 1997. This similar to ostracoderms, basal to sharks.
Figure 2b. Sturgeon mouth animated from images in Bemis et al. 1997. This is similar to ostracoderms and basal to sharks. The barbels are retained buccal cirri.

Muir et al. 2000 report
a burrowing river amphipod about 1 cm long, Corophium spp., is the most important prey for bottom-feeding juvenile and sub-adult white sturgeon. In adult sturgeons,small bottom-dwelling fish, larvae, crayfish, snails, clams and leeches are on their prey list.

So the loss of teeth and the change in diet
reflects a change from open water predation of microscopic forms that other fish would filter to visible worms and larvae living in river bottoms.

This somewhat mirrors more primitive behavior in lancelets
that feed in open waters as juveniles, then burrow tail first in river bottoms and become sessile feeders. One branch of lancelets kept evolving to become crinoids and later, starfish. The other branch, the one that kept active as adults, became vertebrates.

Figure 11.  Manta compared to Thelodus (Loganellia) and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes, distinct from most fish. Note the lack of teeth. 
Figure 3.  Manta compared to Thelodus (Loganellia) and Rhincodon. Note the lack of teeth in this large, open water filter feeders.

This supports the phylogeny
of the large reptile tree (LRT, 1780+ taxa) which recovers the toothless Chondrosteus + Rhinchodon + Manta clade as the proximal descendants of sturgeons. These increasingly larger taxa continue to feed like larval sturgeons on plankton filtered from open water with larger, more anteriorly directed jaws and branchial cavities.

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

The second largest and second most basal shark in the LRT,
the basking shark, Cetorhinus, is likewise toothless and feeds on open water zooplankton.

Phylogenetically
it was not until larval teeth were retained in adults, like Isurus and similar sharks, that made the capture of larger and larger prey in open water conditions possible. Contra tradition,  filter-feeding, like a whale shark, is a a primitive trait, as documented in the LRT.

After marginal teeth appeared on shark jaws, and stayed there in adults,
evolution took several courses, including a return to benthic feeding in guitarfish, sawfish, rays, ratfish all with pavement-like teeth. Sharks with sharp teeth kept their open water feeding habits. Some of these gradually lost the long rostrum and evolved into several forms, including 2m Hybodus close to the base of bony fish represented by 4cm Prohalecites (Fig. 5).

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.

Given the above gathered data points,
now I’m looking for a juvenile osteostracan. Wonder what it looks like? If less bony, as in sturgeons, they might be hard to find.


References
Muir WD, McCabe, Parsley and Hinton 2000. Diet of first-feeding larval and young-of-the-year white sturgeon in the Lower Columbia River. Northwest Science 74(1):25–33.
Sewertzoff AN 1928. The head skeleton and muscles of Acipenser ruthensus. Acta Zoologica 13:193–320.
Zarri LJ and Palkovacs EP 2018. Temperature, discharge and development shape the larval diets of threatened green sturgeon in a highly managed section of the Sacramento River. Ecology of freshwater fish 28(2): https://doi.org/10.1111/eff.12450

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.

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

Squaloraja: more of a paddlefish than a ratfish

One of the strangest looking of all vertebrates,
Squaloraja polyspondyla, nests alone in the large reptile tree (LRT, 1772+ taxa) between the clade of gnathostomes without marginal teeth and those with marginal teeth.

Figure 1. Squaloraja is not the chimaerid everyone thinks it is, but nests with Scapanorhynchus and Mitsukurina in the paddlefish clade.

Figure 1. Squaloraja is not the chimaerid everyone thinks it is, but nests with Scapanorhynchus and Mitsukurina in the paddlefish clade.

Squaloraja polyspondyla (Agassiz 1843, Woodward 1866, Early Jurassic) is traditionally considered a relative of Chimaera, but here nests as a late-survivor of the basalmost taxon with marignal teeth, here named “Marginodonta“, between the basalmost, toothless, gnathostome clade with Chondrosteus at its base, and all other vertebrates with marginal teeth in the LRT with the paddlefish, Polyodon, at its base.

In a pre-cladistic era,
Squaloraja would have been considered a member of the Chondrostei, since it nests between sturgeons and paddlefish. But now in the LRT, so do whale sharks and mantas.

Grogan, Lund and Greenfest-Allen 2012
nested Squaloraja with chimaerids, but that cladogram excluded Squaloraja pre-shark sister taxa recovered in the wider gamut LRT.

Rather than a continuous notochord,
a series of cartilaginous segments is present, convergent with the situation in bony fish. As an Early Jurassic taxon, Squaloraja had plenty of time to develop this one trait.

Figure 2. Polyodon hatchling prior to the development of the long rostrum with maturity.

Figure 2. Polyodon hatchling prior to the development of the long rostrum with maturity.

These taxa were bottom feeders with a large wide rostrum full of sensors for detecting buried prey. Distinct from rays and sturgeons, but like Chondrosteus and paddlefish (Polyodon), the mouth was wide. Several excellent specimens preserve soft parts. It is worth comparing Squaloraja to a hatchling Polyodon (Fig. 2).


References
Agassiz L 1843. Recherches sur les Poissons Fossiles, III (IV), Imprimerie de Petitpierre, Neuchatel, pp. 157-390.
Grogan ED, Lund R and Greenfest-Allen E 2012. The origin and relationships of early chondrichthyans. In: Carrier JC, Musick JA and Heithaus MR (eds) Biology of Sharks and their Relatives, Edition 2. CRC Press, Boca Raton, Florida: 3–30.
Woodward AS 1886. On the anatomy and systematic position of the Liassic selachian Squaloraja polyspondyla Agassiz. Proceedings of the Zoological Society of London, 1886: 527–538.

Other references online here and here.

wiki/Squaloraja

The LRT confirms a 2015 paper: sharks had a semi-bony past

Long et al. 2015
described a few bits and pieces from a Late Devonian shark, Gogoselachus (Fig 1), with a “highly distinctive type of calcified cartilage forming the endoskeleton.”

I came across this 2015 paper a few days ago, long after sharks nested as taxa derived from cartilaginous sturgeon and semi-bony paddlefish ancestors in the Large Reptile Tree (LRT, 1744+ taxa, subset Fig. 2). So having a basal shark with ‘calcified cartilage’ comes as no surprise to the LRT.

Figure 1. Gogoselache restoration based on the few parts shown here.

Figure 1. Gogoselache restoration based on the few parts shown here from Long et al. 2015.

From the Long et al. ‘Background’
“Living gnathostomes (jawed vertebrates) comprise two divisions, Chondrichthyes (cartilaginous fishes, including euchondrichthyans with prismatic calcified cartilage, and extinct stem chondrichthyans) and Osteichthyes (bony fishes including tetrapods).”

This is the traditional view of fish interrelations, the one told in lectures and textbooks. See figure 2 for the more complete LRT view.

“Most of the early chondrichthyan (‘shark’) record is based upon isolated teeth, spines, and scales, with the oldest articulated sharks that exhibit major diagnostic characters of the group—prismatic calcified cartilage and pelvic claspers in males—being from the latest Devonian, c. 360 Mya. This paucity of information about early chondrichthyan anatomy is mainly due to their lack of endoskeletal bone and consequent low preservation potential.”

Figure x. Subset of the LRT focusing on fish.

Figure 2. Subset of the LRT focusing on fish.

From the Long et al. 2015 Methodology/Principal Findings
“Here we present new data from the first well-preserved chondrichthyan fossil from the early Late Devonian (ca. 380–384 Mya) Gogo Formation Lägerstatte of Western Australia. The specimen is the first Devonian shark body fossil to be acid-prepared, revealing the endoskeletal elements as three-dimensional undistorted units: Meckel’s cartilages, nasal, ceratohyal, basibranchial and possible epibranchial cartilages, plus left and right scapulocoracoids, as well as teeth and scales. This unique specimen is assigned to Gogoselachus lynnbeazleyae n. gen. n. sp.”

From the Long et al. 2015 Conclusions/Significance
“The Meckel’s cartilages show a jaw articulation surface dominated by an expansive cotylus, and a small mandibular knob, an unusual condition for chondrichthyans.”

In the LRT the Meckel’s cartilages are scored as fused mandible bones based on ancestral states in which the mandible bones are not fused.

“The scapulocoracoid of the new specimen shows evidence of two pectoral fin basal articulation facets, differing from the standard condition for early gnathostomes which have either one or three articulations.”

“The tooth structure is intermediate between the ‘primitive’ ctenacanthiform and symmoriiform condition, and more derived forms with a euselachian-type base.”

Of special interest is the highly distinctive type of calcified cartilage forming the endoskeleton, comprising multiple layers of nonprismatic subpolygonal tesserae separated by a cellular matrix, interpreted as a transitional step toward the tessellated prismatic calcified cartilage that is recognized as the main diagnostic character of the chondrichthyans.”

In the LRT phylogenetic analysis, rather than a few interesting and traditionally unexpected traits, elucidates interrelationships. Having bony traces in a basal shark skeleton could have been predicted from the LRT, but the fish portion of the LRT came later, this time providing confirmation rather than prediction.

The Long et al. 2015 paper
earned a fair bit of publicity five years ago.

From Phys.org
“Fossil ancestor shows sharks have a bony past.
This study further supports the idea that sharks must have evolved from bony primitive ancestors and lost their bone early on in the race as they acquired their predatory body shape.”

From: theconversation.com
“No bones about it. Sharks evolved cartilage for a reason.
Most people know that sharks have a distinctive, all-cartilage skeleton, but now a fossil from Western Australia has revealed a surprise ‘missing link’ to an earlier, more bony form of the fish.”

“In testing fossil remains discovered by Professor Long in July 2005 at Gogo in the Kimberley in Western Australia, detailed CT scanning analysis has shown that the three-dimensional remnant skeleton contains a small proportion of bone as well as cartilage.”

“Because sharks and rays have entirely cartilaginous skeletons, Professor Long said it was traditionally thought that they were part of a primitive evolutionary pathway, and that bone in other fish was the more advanced condition. But a series of discoveries in recent years has suggested that sharks are “more evolutionarily derived”, and are likely to be descended from bony ancestors.”


References
Long JA, Burrow CJ, Ginter M, Maisey JG, Trinajstic KM, et al. 2015. First Shark from the Late Devonian (Frasnian) Gogo Formation, Western Australia Sheds New Light on the Development of Tessellated Calcified Cartilage.” PLoS ONE10(5): e0126066. DOI: 10.1371/journal.pone.0126066

The rest of Lonchodraco probably looks like this large unnamed ornithocheird

Only the deep toothy jaw tips,
of the pterosaur Lonchodraco giganteus (Hooley 1914; Rodrigues & Kellner 2013; NHMUK PV 39412; originally Pterodactylus giganteus Bowerbank 1846; Fig. 1) are known. Ever wonder what the rest of this pterosaur looked like?

Well,
the 174-year wait is over.

Figure 1. Lonchodraco jaw tips. Colors added here.

Figure 1. Lonchodraco jaw tips. Colors added here. For the rest of this genus, see figure 2. The nasal (pink) is laminated between the premaxilla (yellow) and maxilla (green). The jugal (blue) also makes an appearance.

What little is known of Lonchodectes turns out to look like
the (so far) unnamed large ornithocheirid, SMNK PAL 1136 (Fig. 2) one of the largest of all flying pterosaurs. The very few parts they have in common are virtually identical, except for size (note the scale bars provided).

Figure 2. The unnamed giant ornithocheirid, SMNK PAL 1136 has a rostrum quite similar to that of Lonchodectes.

Figure 2. The unnamed giant ornithocheirid, SMNK PAL 1136 has a rostrum quite similar to that of Lonchodectes. With such giant wings, soaring over wave tops would have been ideal, dipping occasionally to feed without getting wet.


As one of the largest flying pterosaurs,

SMNK PAL 1136 (Figs. 2, 3) presents no vestigial terminal wing phalanges. No hyper-elongated neck cervicals are present. This pterosaur was built to soar like a big pelican.

Sorry, giant azhdarchids lovers 
(Fig. 3). Those were not volant, as we learned earlier here. They grew to be so big AFTER they became flightless, like flightless birds do. Giant azhdarchids DO have vestigial wing phalanges and a hyper-elongated neck.

Figure 1. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale.

Figure 3. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale.

Earlier workers 
did not match Lonchodraco to the SMNK PAL 1136 specimen. Earlier workers did not name the SMNK specimen. Perhaps someone is working on that specimen at present and other workers are giving him/her the honor/duty of naming it.

Wonder if
the Lonchodraco name will stick to the SMNK specimen?

Recently, Martill et al. 2020 took a close look
at the foramina in the jaw tips of Lonchodraco and thought they indicated enhanced sensitivity of the rostrum tip, which implied tactile feeding. With such giant wings, soaring over wave tops would have been likely, dipping occasionally to feed without getting the wings wet.

Odd that the top workers at the top universities
have decided to spend their time examining tiny pits on a broken 174-year-old pterosaur snout while ignoring the origin of pterosaurs… while ignoring many dozen complete pterosaurs that should be in phylogenetic analysis… while ignoring the lepidosaurs that gave rise to the ancestors of pterosaurs. Unfortunately, that’s the world academics live in today. They keep trying to not upset the lectures and textbooks from which they make their living. Apparently if academics focus on the details they won’t have to worry about the big picture. No one will ever know the difference if no one points out the elephant in the room.


References
Averianov AO 2020. Taxonomy of the Lonchodectidae (Pterosauria, Pterodactyloidea). Proceedings of the Zoological Institute RAS. 324 (1): 41–55. doi:10.31610/trudyzin/2020.324.1.41
Bowerbank JS 1846. On a new species of pterodactyl found in the Upper Chalk of Kent (Pterodactylus giganteus). Quarterly Journal of the Geological Society of London. 2: 7–9.
Bowerbank JS 1848. Microscopical observations on the structure of the bones of Pterodactylus giganteus and other fossil animals”. Quarterly Journal of the Geological Society. 4: 2–10.
Martill DM, Smith RE, Longrich N and Brown J 2020. Evidence for tactile feeding in pterosaurs: a sensitive tip to the beak of Lonchodraco giganteus (Pterosauria, Lonchodectidae) from the Upper Cretaceous of southern England. Cretaceous Research
Available online 3 September 2020, 104637 Cretaceous Research https://doi.org/10.1016/j.cretres.2020.104637
Rodrigues T and Kellner A 2013. Taxonomic review of the Ornithocheirus complex (Pterosauria) from the Cretaceous of England. ZooKeys. 308: 1–112. doi:10.3897/zookeys.308.5559

wiki/Lonchodraco

Toothy Calamopleurus enters the LRT with Amia

Updated January 16, 2021
with additional taxa and some score changes Calampleurus now nests with Amia.

Short one today.
If you like fish with big teeth,
you’ll like Calamopleurus (Agassiz 1841, Early Cretaceous; Figs. 1, 2), a taxon typically considered a relative of the bowfin, Amia.

Figure 1. The skull of Calamopleurus from Long 1995 and reconstructed using DGS methods.

Figure 1. The skull of Calamopleurus from Long 1995 and reconstructed using DGS methods.

When you add in a few more taxa,
Calamopleurus is derived from Trachinocephalus, the extant blunt-nosed lizardfish (Fig. 3) in the large reptile tree (subset Fig. x), with Amia.

Figure 2. Another specimen diagram of Calamopleurus.

Figure 2. Another specimen diagram of Calamopleurus. Looks like a bowfin, but it is closer to lizardfish.

Nesting where it does in the LRT,
(Fig. x) Calamopleurus is basal to virtually all other ray fin bony fish, but Trachinocephalus is close to our own direct ancestry… and also sea horses, sailfish, catfish, spiny sharks and placoderms. That means this fish and this clade of fish had its genesis and initial radiation 300 million years earlier, in the Silurian.

Figure 3. The extant blunt-nosed lizardfish, Trachinocephalus, nests with Calamopleurus in the LRT.

Figure 3. The extant blunt-nosed lizardfish, Trachinocephalus, nests with Calamopleurus in the LRT.

It should come as no surprise
that this clade of fish also includes several hyper-toothy taxa, including Chiasmodon (Fig. 4) and Malacosteus (Fig. 5).

Figure 2. Chiasmodon from Gregory 1938, here colorized. Compared to the lizardfish, Trachinocephalus, in figure 3.

Figure 4. Chiasmodon from Gregory 1938, here colorized.

Based on the preponderance of big teeth
at the base of the big bony fish split (Fig. x), evidently ‘long, sharp teeth’ was a primitive trait later sometimes lost in both lineages.

The LRT proposes a hypothesis of interrelationships
previously untested with extant and extinct taxa from several traditional clades here (Fig. x) tested together for the first time.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Figure x. Subset of the LRT, focusing on fish for July 2020.

LRT change:
The enigmatic wide-mouth, big-eyed fish, Doliodus, now nests with the spiny sharks, Homalacanthus and Acanthoides. a few nodes apart from Xenacanthus, which also has twin-spiked teeth.


References
Agassiz L 1833-43. Recherches sur les poissons fossiles. Imprimerie de Petitpierre et Prince, Neuchâtel.