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?Two more convergent Polyprotodonty transitions to Diprotodonty ...

2026-10-29T23:56:00Z

?Two more convergent Polyprotodonty transitions to Diprotodonty

Yesterday we looked at
a transitional taxon, Gymnobelideus, that linked a polyprotodont ancestor, Dromiciops, to a diprotodont descendant, Petaurus. All three are extant marsupial taxa.
These in turn gave rise to placental 2 multituberculates, rodents and their kin.
Figure 1. Somewhere between Monodelphis kumasi and Acdestis the lower incisors became enlarged, reduced in number and anteriorly-oriented giving rise to ?two more convergent clades displaying diprotodont dentition in the mandible.
Today we will look at
a second and possible third origin for a diprotodont dentition in marsupials like Macropus, the kangaroo, and giant Diprotodon, the namesake for this grade (Fig 1).
Unfortunately, these large reptile tree (LRT) convergent clade topologies split the traditional monophyly of the former monophyletic clade/order Diprotodontia.
If this changes, and it could, I will let you know.
What about Stylindon and kin?
Stylinodontids are placental taxa that convergently develop a diprotodont mandible from ancestors like Ptolemaia, Arctocyon and Sinonyx in the LRT. Traditionally stylinodontids are marsupial taeniodonts, like Trogosus (Fig 1).
The LRT does not recover the traditional stylindont/taeniodont interrelationship.
References
wiki/Diprotodontia

https://pterosaurheresies.wordpress.com/2026/10/29/two-more-convergent-polyprotodonty-transitions-to-diprotodonty/

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One Polyprotodonty transition to Diprotodonty finds a ...

2026-10-28T23:26:07Z

One Polyprotodonty transition to Diprotodonty finds a transitional taxon

Some marsupials
have five premaxillary incisors and four dentary incisors – all about the same size. Dromiciops (Fig 1 top) is an example of that morphology = polyprotodonty = ‘many front teeth’.
This is the plesiomorphic condition for all tetrapods and their finned ancestors.
Other marsupials
greatly enlarge the central incisors of both the premaxilla and dentary. Petaurus (Fig 1 right) is an example of that morphology = diprotodonty = ‘two front teeth’. The dentary is much shorter than the rostrum which accommodates the enlarged, elongated and forward-facing lower incisors
The placental 2 clade that includes multituberculates and rodents (yes, including rabbits and manatees) are derived from marsupials with diprotodonty. .
Paleontologists know this transition happened.
Unfortunately, paleontologists have not yet identified transitional taxa sharing traits, gaining traits and losing traits that model actual evolutionary events.
Genes have not been helpful here despite all the extant taxa (Fig 1) with deep roots.
The extremely rare Leadbeater’s possum, Gymnobelideus
(Fig 1 left) from a geographic pinpoint in South Australia is similar in size, shape and morphology to the South American Monito del monte, Dromiciops (Fig 1 top), and the flying phalanger, Petaurus (Fig 1 right). These three share a long list of traits – but the teeth are different – evolving from the primitive to the derived condition with Gymnobelideus as the only tested transitional taxon.
Figure 1. At top: Dromiciops has a full arcade of teeth that are similar in size other than the upper canine which was also absent in ancestors. At left: Gymnobelideus has one less upper incisor and the fourth one is a vestige. At right Petaurus has three upper incisors. As in Gymnobelideus incisors 1 and 2 are laminated and incisors 3 and 4 are vestiges. No phylogenetic miniaturization at this transition.
In this evolutionary sequence
(Fg 1) the number of premaxillary teeth disappear from back to front while the central = anterior tooth gets bigger. Meanwhile, as the mandible shortens, the first two dentary teeth enlarge, elongate and laminate while incisors 3 and 4 become leftovers. The lower canine (orange) is disappears. There are three dentary premolars in all three taxa, which helps identify what teeth remain despite their reduction and shape change.
Note the lower incisors of Dromiciops (Fig 1 top) are already oriented anteriorly on a slightly shortened mandible. The canine (orange) and no longer sharp is still large and present.
According to Wikipedia Leadbeaters_possum
“Their diet is omnivorous: feeding on a range of wattle saps and exudates, lerps, and a high proportion of arthropods which they find under the loose bark of eucalypts, including spiders, crickets, termites and beetles. Plant exudates make up 80% of their energy intake, but the protein provided by the arthropods is essential for successful breeding.”
Diet drives tooth evolution.
These are all extant taxa. Their phylogenetic split preceded the geologic breakup of Gondwanaland around 180 million years ago. So these genera saw dinosaurs.
This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.
References
wiki/Diprotodontia
wiki/Leadbeaters_possum

https://pterosaurheresies.wordpress.com/2026/10/29/one-polyprotodonty-transition-to-diprotodonty-finds-a-transitional-taxon/

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Gaffneylania: an ‘early’ horned turtle from Eocene Patagonia ...

2026-10-20T15:21:32Z

Gaffneylania: an ‘early’ horned turtle from Eocene Patagonia

Sterli et al 2015
described Eocene Gaffneylania as one of the earliest known meiolaniids – the large horned turtles (Fig 1).
Unfortunately the roof of the skull is not preserved. Skull scutes further obscure the anatomy.
Figure 1. Horned turtles to scale. Ninjemys is primitive among these.
The small bit of shell
that is known had a serrated margin. The specimen is incompletely known. So no reconstruction has been attempted.
The name honors
AMNH turtle paleontologist Eugene S. Gaffney, a specialist in meiolaniids.
Figure 2. Mongolocheys and Cubutemys nest together near, but not at, the base of the hard shell turtles. Both were considered sisters to Meiolania and Niolamia by prior workers who did not include Elginia in phylogenetic analysis.
The authors considered
hornless Chubutemeys (Fig 2) a basal meiolanid. The authors had their cladogram upside-down. It lacked horned pareiasaurs (Fig 1). Chubutemys is a derived hardshell turtle in the LRT.
Meiolanids are the most primitive
hardshell turtles in the large reptile tree (LRT, 2340 taxa). They are derived from Elginia (Fig 1) and Bunostegos (Fig 1). Softshell turtles arose from the small horned pareiasaur, Sclerosaurus in the LRT.
Pareiasaurs are traditionally Middle to Late Permian
in temporal range. Since turtles are extant with some marine genera, that means pareiasaurs still live among us… some chasing cats on little skateboards on YouTube.
References
Sterli J, de la Fuente MS and Krause JM 2015. “A new turtle from the Palaeogene of Patagonia (Argentina) sheds new light on the diversity and evolution of the bizarre clade of horned turtles (Meiolaniidae, Testudinata)”. Zoological Journal of the Linnean Society. 174 (3): 519–548.
wiki/Chubutemys
wiki/Gaffneylania
wiki/Pareiasauria

https://pterosaurheresies.wordpress.com/2026/10/20/gaffneylania-an-early-horned-turtle-from-eocene-patagonia/

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What is Ammonitritor scientiacivium? Sander et al 2926 considered ...

2026-10-19T18:40:21Z

What is Ammonitritor scientiacivium?

Sander et al 2926
considered Ammonitritor (Figs 1–3) a genus of early ichthyosauriform in the family Omphalosauridae (Fig 2), known from the Early Triassic of Norway.
Figure 1 Early Triassic Ammonitritor scientiacivium PGE LE 2024.0.264 from Sander et al 2026. Compared to slightly larger ?Shastasaurus YGMIR SPC VO3108.
Backstory
In the large reptile tree (LRT, 2340 taxa) Omphalosaurus (Fig 2) is a basal enaliosaur = marine younginiform, not closer to ichthyosaurs + mesosaurs + thalattosaurs than to sauropterygians = prior to that split. That was a very difficult reconstruction to make = could have large errors.
Figure 2. Omphalosaurus nevadanus, MBG 1500, the Austria specimen, skull portion in situ, mandible parts, skull parts and reconstruction with matching colors based on Sinosaurosphargis, the only other taxon with such a large set of splenials. The premaxillae are wider than the dentaries. Distinct from Sinosaurosphargis, the premaxillae were much enlarged.
Since the Ammonitritor paper is behind a paywall,
I do not know if the ?Mikadocephalus ichthyosaur YGMIR SPC VO3108 (Fig 1) was compared. There is also a thalattosaur, Miodentosaurus (Fig 3), with similar traits and proportions to the new taxon – along with important differences.
Figure 3. Ammonitritor compared to the thalattosaur Miodentosaurus.
The authors also linked
the basal pachypleurosaurs, Cartorhynchus and Sclerocormus (Fig 4) with Omphalosaurus (Fig 2).
The LRT does not recover that interrelationship.
Figure 4. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms.
Given these several similar taxa from disparate clades,
I’m going to wait for more information before adding Ammonitritor to the LRT. That short snout, deep convex maxilla and other traits pop up several times in the resurrected clade Enaliosauria.
References
Sander PM et al (4 co-authors) 2026. Omphalosauridae (Ichthyosauriformes): enigmatic marine reptiles in the global recovery from the end‐Permian extinction. Biological Reviews. doi:10.1002/brv.70208
wiki/Ammonitritor

https://pterosaurheresies.wordpress.com/2026/10/19/what-is-ammonitritor-scientiacivium/

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Maybe Apternodus is an extinct hedgehog. Maybe an extinct shrew. ...

2026-10-18T08:25:14Z

Maybe Apternodus is an extinct hedgehog. Maybe an extinct shrew.

Maybe both.
This will not be tested and (hopefully) decided until Monday.
So place your bets over the weekend.
Earlier
Eocene-Oligocene Apternodus (Figs 1, 2) nested with Scutisorex the extant shrew (Fig 1) in the large reptile tree (LRT, 2340 taxa). That seemed logical at the time.
Today’s question is: Is this a valid sister taxon interrelationship?
There might be a competing sister (Fig 2).
Figure 1. Apternodus and Scutisorex to scale. The similarities are strong here. Note the anteriorly leaning occiput, lack of a zygomatic arch and polyprotodont dentary incisor.
Apternodus has bulbous cheek teeth
similar to those of sauropterygian placodonts – by convergence – and an upturned premaxilla. At present, those teeth are unique in the mammal subset of the LRT. The dentary presents polyprotodonty = rodent-like incisor, as in Scutisorex (Fig 1).
Maybe it’s those teeth, but Apternodus has been a nagging wild card in scoring the LRT.
Today, comparing extinct Apternodus
to the extant lesser hedgehog Hemiechinus (Fig 2) presents an interesting alternative = competing sister taxon possibility. Both share a rare anterior leaning occiput and more common polyprotodont dentary incisor (Fig 2) as in Scutisorex (Fig 1).
Figure 2. Apternodus compared to the lesser hedgehog, Hemiechinus. Note the large number of similar trait and overall size. The zygomatic arch may be missing due to taphonomy, not phylogeny.
You’ll note the DGS colors have shifted
for Apternodus from figure 1 to figure 2. This reflects the human factor = trying to match traits to another taxon while learning what is what today vs several years ago (Fig 1).
Remember, there is no instruction manual. Frustration mingles daily with insight as this vexing problem = the mammal subset of the LRT has now been under scrutiny for 2.5 years, much longer than any other subset.
References
Asher RJ et al (4 co-authors) 2002. Morphology and relationships of Apternodus and other extinct, zalambdodont, placental mammals. Bulletin of the AMNH 273:1–117.
Matthew WD 1903. The fauna of the Titanotherium Beds at Pipestone Springs, Montana. Bulletin of the American Museum of Natural History 19(6):197–226.
wiki/Scutisorex
wiki/Apternodus – not yet posted

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#fig #apternodus #maybe #extinct #scutisorex #lrt #hedgehog #hemiechinus #bulletin #both

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Chondrosteus under review seven years later We looked at ...

2026-10-17T16:21:17Z

Chondrosteus under review seven years later

We looked at
Chondrosteus (Fig 1) back in 2019 back when there were far fewer fish taxa in the large reptile tree (LRT, 2340 taxa).
Hilton and Forey 2009 reported, “Chondrosteus was a basal member of the order Acipenseriformes (sturgeons, paddlefishes and their fossil relatives) from the Lower Jurassic of England.”
That’s the tradition taught in academic textbooks.
Figure 1. Cetorhinus, Polyodon, Chondrosteus and Strongylosteus in phylogenetic order demonstrating the fourth origin of the operculum.
Hilton and Forey
nested Chondrosteus between Birgeria and Piepiaosteus employing only 11 genera in their taxon list (that includes several species of the sturgeon Acipenser and several species from other genera).
In the LRT Chondrosteus. Piepiaosteus and the paddlefish, Polyodon, nest with the basking shark, Cetorhinus, demonstrating the convergent development of gill covers.
Relative to the LRT, taxon exclusion is apparent in the Hilton and Forey cladogram. Apparently they were focused on a few traits = ‘Pulling a Larry Martin‘.
Figure 2. Image from 2022 when there were far fewer fish in the LRT. Traditional origin of jaws from the ostracoderm, Hemicyclaspis, Thelodus, Acipenser (sturgeon) and Chondrosteus. Now, with more fish in the LRT, there were several, at least three) origins for jaws. Add taxa = learn something. You can see the strong resemblance between Acipenser and Chondrosteus overcome by the LRT when the basking shark, Cetorhinus, entered the taxon list.
As an experiment,
see what happens when more pertinent taxa are added to your own fish cladogram. Use the last common ancestor method based on a long list and a wide gamut of taxa.
Be open and ready to a new experience.
References
Agassiz L 1848. Nomenclatoris zoologici index universalis: continens nomina systematica classium, ordinum, familiarum et generum animalium omnium, tam viventium quam fossilium, secundum ordinem alphabeticum unicum disposita, adjectis homonymiis plantarum, nec non variis adnotationibus et emendationibus.
Egerton PdMG 1858. On Chondrosteus, an Extinct Genus of the Sturionidaek, Found in the Lias Formation at Lyme Regis. Philosophial Transactions of The Royal Society of London 148:871–885.
Hilton EJ and Forey PL 2009. Redescription of Chondrosteus acipenseroides Egerton, 1858 (Acipenseriformes, †Chondrosteidae) from the lower Lias of Lyme Regis (Dorset, England), with comments on the early evolution of sturgeons and paddlefishes. Journal of Systematic Palaeontology. 7(4):427–453.
wiki/Chondrosteus

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