Anteosaurus: a killing machine? No.

Benoit et al. 2021
“reconstruct Anteosaurus [Figs. 1-4] as an agile terrestrial predator based on the enlarged fossa for the floccular lobe of the cerebellum and semicircular canals of the inner ear.” 

Yes, that’s what they wrote. Not the teeth. Not the limbs. The inner ear.

Figure 6. Anteosaurus scale model.

Figure 1. Anteosaurus scale model.

From the Material and Methods section:
“The disarticulated skull (BP/1/7074) of a juvenile Anteosaurus magnificus from the middle Permian of the South African Karoo…”

The BP/1/7074 specimen (Figs. 2–4) does not nest with Anteosaurus (Figs. 1–4) in the Therapsid Skull Tree (TST; Fig. 3) as we learned earlier here after testing (Fig. 3).

Figure 2. Kruger et al. 2017 figure 21. provided "Ontogenetic changes in the skull of Anteosaurus; A. juvenile; B, intermediate sized; C, adult sized, redrawn from Kammerer 2011. Their figure 20 labeled the intermediate sized skull as Titanophoneus. So this is a phylogenetic series, not an ontogenetic one.

Figure 2. Kruger et al. 2017 figure 21. provided “Ontogenetic changes in the skull of Anteosaurus; A. juvenile; B, intermediate sized; C, adult sized, redrawn from Kammerer 2011. Their figure 20 labeled the intermediate sized skull as Titanophoneus. So this is a phylogenetic series, not an ontogenetic one.

 

Figure 3. Therapsid Skull Tree with herbivorous clades colored.

Figure 3. Therapsid Skull Tree with herbivorous clades colored.

Figure 1. Anteosaurus magnifies compared to the smaller and coeval BP/1/7074 specimen others considered a juvenile. Other more closely related specimens in the TT are also shown alongside BP/1/7074 specimen.

Figure 4. Anteosaurus magnifies compared to the smaller and coeval BP/1/7074 specimen others considered a juvenile. Other more closely related specimens in the TT are also shown alongside BP/1/7074 specimen.

Phylogenetic context is paramount and required.
There are several problems with the conclusions of Benoit et al. 2021.

  1. The specimen is not Anteosaurus.
  2. Dinocephalians were all herbivores.
  3. Those huge teeth were as sharp as bananas, like hippo teeth.
  4. The bones of the inner ear do not determine whether you are predator or prey.

What is going on
at the universities nowadays?? Is phylogenetic analysis old-fashioned? Let’s get back to basics.


References
Benoit J, Kruger A, Jirah S, Fernandez V and Rubidge BS 2021. Palaeoneurology and palaeobiology of the dinocephalian therapsid Anteosaurus magnificus. Acta Palaeontolgocia Polonica 66(X):xxx-xxx. https://doi.org/10.4202/app.00800.2020

https://phys.org/news/2021-03-prehistoric-machine-exposed.html?fbclid=IwAR0ZhQ_5_Qgn4LscUgK0rUVcUv8XmwDAdtKdDXJJ6pHNG3M3UAjvRpw9d-s

Correction: European eels are neotonous swordfish

Before you say, “That’s crazy!” did you ever notice
that swordfish lack ribs and pelvic fins (Fig. 4)? So do European eels.

More importantly, did you ever notice
that baby swordfish look like eels (Fig. 4)? Okay. With that in mind, let’s start with a little backstory and cover all the bases.

Traditionally swordfish have been allied with 
barracuda, marlin and several extinct billfish, including Blochideae (i.e. Blochius, Fig. 4), based on overall appearance, open sea niche and apex predator status. According to Wikipedia, “They [swordfish] are the sole member of their family, Xiphiidae.” Gregory and Conrad  1937 compared the morphologies of the sailfish and swordfish. Earlier I followed the lead of these experts in nesting the sailfish, Istiophorus (Figs. 5, 7), and the swordfish, Xiphiias, with the barracuda, Sphyraena. That was a mistake.

Today we’ll compare
swordfish and sailfish morphology to two other more closely related taxa: the anchovy, Elops (Fig. 6) and the European eel, Anguilla, which turns out to be more closely related to swordfish despite their outward differences as adults. Turns out that swordfish go through a metamorphosis as they develop from eel-like hatchlings with teeth (Fig. 4).

The LRT scores skeletal traits 
rather than superficial morphologies, which are always prone to reversal and convergence. The large reptile tree (1793+ taxa) is designed to test taxa together that have not been tested together before. Some surprises were recovered earlier using this method here, here and here.

In their description of Bavarichthys
(Fig. 1) Arratia and Tischlinger 2010 did not mention or test the eel, Anguilla, or the swordfish, Xiphias. Turns out, they should have done so.

Recent revisions
of several fish taxa (now that I have 250 fish taxa and the experience that brings to bear) reveal a hitherto overlooked hypothesis of interrelationships between eels and swordfish. Sound crazy? Keep reading. This is one of those ‘moment of discovery’ moments I want to share with you.

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.

Let the cheek plates evolve away in Bavarichthys
(Fig. 1) and you’l have the basic skull of both swordfish (Fig. 2) and European eels (Fig. 3). Note the triangular profile, the slender insertion of the nasal between the anterior frontals, the extreme brevity of the post-orbital portion of the skull, including a vertical quadrate. No other tested fish taxa have these traits.

Figure 2. Diagram of the swordfish (Xiphias) skull. Compare to figures 1 and 3.

Figure 2. Diagram of the swordfish (Xiphias) skull. Compare to figures 1 and 3.

Billfish came first. 
The European eel, Anguilla, is derived from swordfish, sailfish and Late Jurassic Bavarichthys. Hatchlings of swordfish are eel-like (Fig. 4) and Bavarichthys-like (Fig. 1). That means European eels are neotonous swordfish. They achieve adulthood while still in the hatchling swordfish stage. European eels also develop traits not found in swordfish, like additional vertebrae and a long, low operculum. European eels don’t develop pelvic fins of dorsal ribs. Neither do swordfish.

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

Figure 3. Skull of Anguilla, the European eel, compares well with that of Bavarichthys. Note the loss and reduction of preorbital bones.

Earlier the LRT nested
Late Jurassic Bavarichthys with closely related anchovies (genus: Elops), then with more closely related European eels (genus: Anguilla). Now it nests basal to both swordfish and European eels.

Other eels,
like the moray eel (Gymnothorax) and electric eel (Electrophorus) nest elsewhere, both near the base of the bony fish. So eels were in the gene pool.

Figure 4. Swordfish ontogeny (growth series). Hatchings have teeth, a short bill and an eel-like body still lacing pelvic fins.

Figure 4. Swordfish ontogeny (growth series). Hatchings have teeth, a short bill and an eel-like body still lacing pelvic fins. Hatchlings go through an eel-like phase and a sailfish-like phase.

Xiphias gladius
(Linneaus 1758; Gregory and Conrad 1937; up to 4.5m in length) is the extant swordfish, nesting between Bavarichthys and Anguilla. 1cm long hatchlings more closely resembled little eels, then growing to little sailfish before reducing the long dorsal fin. The sword is not used to spear, but to slice and maim smaller fish traveling in schools. The pelvic fins and ribs are absent, as in eels. Larger females produce more eggs, up to 29 million.

Figure 5. Skull of the sailfish, Istiophorus. Compare to Elops in figure 6.

Figure 5. Skull of the sailfish, Istiophorus. Compare to Elops in figure 6.

Figure 2. Elops is the extant anchovy. Compare to Bavaricthys in figure 1 and Istiophorus in figure 5.

Figure 6. Elops is the extant anchovy. Compare to Bavaricthys in figure 1 and Istiophorus in figure 5.

Figure 1. Istiophorus, the sailfish, nests with the cobria (Fig. 2) in the LRT, not with the swordfish.

Figure 7. Istiophorus, the sailfish, nests with the anchovy, Elops, not with, but close to the sailfish, Xiphias.

Sailfish have long slender pelvic fins,
like those of anchovies, unlike swordfish and eels. Sailfish have a broad postorbital, like anchovies, unlike swordfish. Sailfish have a zig-zag frontal-nasal suture, like anchovies, unlike swordfish. The list of subtle, but scoreable differences continues. More importantly, no other tested taxa share more traits with swordfish and sailfish than eels and anchovies, respectively.

Figure 8. Subset of the LRT focusing on ray fin fish. Eel-like taxa are highlighted.

Figure 8. Subset of the LRT focusing on ray fin fish. Eel-like taxa are highlighted.

With the sailfish and swordfish gone, where does that leave the lonely barracuda?
In the LRT the barracuda nests with the similar long-bodied remora (Remora) and cobia (Rachycentron), derived from the mahi-mahi (Coryphaena) all with mandibular prognathism. This is non-tradional. Other workers prefer to nest billfish with barracuda.


References
Arratia G and Tischlinger H 2010. The first record of Late Jurassic crossognathiform fishes from Europe and their phylogenetic importance for teleostean phylogeny. Mitteilungen aus dem Museum für Naturkunde in Berlin. Fossil Record; Berlin 13(2): 317–341.
Gregory WK and Conrad GM 1937. The comparative anatomy of the swordfish (Xiphias) and the sailfish (Istiophorus). The American Museum Novitates, 952:1-25.
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

https://pterosaurheresies.wordpress.com/2020/07/04/bavarichthys-a-late-jurassic-solnhofen-anchovy/

wiki/Istiophoriformes

wiki/Swordfish

 

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.

Ichthyostega and Acanthostega: secondarily more aquatic

More heresy here
as the large reptile tree (LRT, 1036 taxa) flips the traditional order of fins-to-feet upside down. Traditionally the late Devonian Ichthyostega and Acanthostega, bridge the gap between lobe-fin sarcopterygians, like Osteolepis.

In the LRT
Acanthostega, ‘the fish with limbs’, nests at a more derived node than its precursor, the more fully limbed, Ossinodus (Fig. 1). Evidently neotony, the retention of juvenile traits into adulthood, was the driving force behind the derived appearance of Acanthostega, with its smaller size, stunted limbs, smaller skull, longer more flexible torso and longer fin tail.

Figure 1. Ossinodus is the more primitive taxon in the LRT compared to the smaller Acanthostega, the tadpole of the two.

Figure 1. Ossinodus is the more primitive taxon in the LRT compared to the smaller Acanthostega, essentially the neotenous ‘tadpole’ of the two.

Likewise
Ichthyostega is more derived than both fully-limbed Ossinodus and Pederpes, which had five toes. As in Acanthostega, the return to water added digits to the pes of Ichthyostega. In both taxa the interosseus space between the tibia and fibula filled in to produce a less flexible crus.

Figure 2. Ossinodus, Pederpes were more primitive than the more aquatic Icthyostega.

Figure 2. Long-limbed Ossinodus and Pederpes were more primitive than the more aquatic Icthyostega.

So, Acanthostega and Ichthyostega were not STEM tetrapods.
Instead, they were both firmly nested within the clade Tetrapoda. Ossinodus lies at the base of the Tetrapoda. The proximal outgroups are similarly flattened Panderichthys and Tiktaalik. The extra digits displayed by Acanthostega and Ichthyostega may or may not tell us what happened in the transition from fins to feet. We need to find a derived Tiktaalik with fingers and toes.

Figure 3. Tiktaalik specimens compared to Ossinodus.

Figure 3. Tiktaalik specimens compared to Ossinodus.

In cases like these
it’s good to remember that ontogeny recapitulates phylogeny. Today and generally young amphibians are more fish-like (with gills and fins) than older amphibians.

It’s also good to remember
that the return to the water happened many times in the evolution of tetrapods. There’s nothing that strange about it. Also the first Devonian footprints precede the Late Devonian by tens of millions of years.

Figure 4. From the NY Times, the traditional view of tetrapod origins.  Red comment was added by me.

Figure 4. From the NY Times, the traditional view of tetrapod origins. 

Phylogenetic analysis teaches us things
you can’t see just by looking at the bones of an individual specimen. A cladogram is a powerful tool. The LRT is the basis for many of the heretical claims made here. You don’t have to trust these results. Anyone can duplicate this experiment to find out for themselves. Taxon exclusion is still the number one problem that is largely solved by the LRT.

You might remember
earlier the cylindrical and very fish-like Colosteus and Pholidogaster convergently produced limbs independently of flattened Ossinodus, here the most primitive taxon with limbs that are retained by every living tetrapod. By contrast, the Colosteus/Pholidogaster experiment did not survive into the Permian.

References
Ahlberg PE, Clack JA and Blom H 2005. The axial skeleton of the Devonian trtrapod Ichthyostega. Nature 437(1): 137-140.
Clack JA 2002.
 Gaining Ground: The origin and evolution of tetrapods. Indiana University Press.
Clack JA 2002. An early tetrapod from ‘Romer’s Gap’. Nature. 418 (6893): 72–76. doi:10.1038/nature00824
Clack JA 2006. The emergence of early tetrapods. Palaeogeography Palaeoclimatology Palaeoecology. 232: 167–189.
Jarvik E 1952. On the fish-like tail in the ichtyhyostegid stegocephalians. Meddelelser om Grønland 114: 1–90.
Jarvik E 1996. The Devonian tetrapod Ichthyostega. Fossils and Strata. 40:1-213.
Säve-Söderbergh G 1932. Preliminary notes on Devonian stegocephalians from East Greenland. Meddelelser øm Grönland 94: 1-211.
Warren A and Turner S 2004. The first stem tetrapod from the Lower Carboniferous of Gondwana. Palaeontology 47(1):151-184.
Warren A 2007. New data on Ossinodus pueri, a stem tetrapod from the Early Carboniferous of Australia. Journal of Vertebrate Paleontology 27(4):850-862.

wiki/Ichthyostega
wiki/Acanthostega
wiki/Ossinodus
wiki/Pederpes