Cui et al document the heretofore missing half of the small-eyed ‘placoderm’, Entelognathus

Cui et al wrote,
“The 425-million-year-old fish Entelognathus (Fig 1) combines an unusual mosaic of characters typically associated with jawed stem gnathostomes or crown gnathostomes. Strikingly, its scales are large and some are rhomboid, bearing distinctive peg-and-socket articulations; this combination was previously only known in osteichthyans and considered a synapomorphy of that group.”

Don’t rely on traits to define a clade. We call this “Pulling a Larry Martin.” Instead use the last common ancestor method in phylogenetic analysis (Fig 2) and then describe the traits, making allowances for possible (or probable) convergence elsewhere.

Taxon exclusion appears to be responsible
for the phylogenetic issues that vexed these authors. By testing more taxa in the large reptile tree (LRT, 2306 taxa, Fig 2) Entelognathus nested with other very similar taxa with robust scales, like Guiyu, Miguashaia and Dialipina. All four nested between traditional placoderms and traditional catfish, including Hoplosternum, the extant armored catfish. Among the three closest relatives in the LRT only Guiyu is mentioned in the Cui et al text. Catfish are not usually included in placoderm analyses.

Figure 1. Enteolgnathus model in two views from Cui et al 2023.. LRT related taxa added here include Dialipina, Miguashaia and Guiyu. Note all four share a similar size, overall shape and differ only in the subtle details. All four are heavily scaled.

Cui et al wrote,
“The presence in Entelognathus of an anal fin spine, previously only found in some stem chondrichthyans, further illustrates that many characters previously thought to be restricted to specific lineages within the gnathostome crown likely arose before the common ancestor of living jawed vertebrates.”

Anal fins, rather than spines, are preserved in two LRT related taxa (Fig 1). The anal portion of Guiyu is not exposed. A tiny primitive taxon, Shenacanthus, has an anal spine seen here.

The authors made the traditional mistake of assuming a single genesis of jaws in living vertebrates. The LRT falsified that in October 2023.

Figure 2. Subset of the LRT focusing on placoderms and kin surrounding Entelognathus. Here it nests with similar taxa with small eyes and large scales including Dialipina, Miguashaia and Guiyu. Only the latter is mentioned in the text.

Cui et al wrote,
“The phylogenetic analysis placed Entelognathus and Qilinyu (Fig 3) in a clade as the immediate sister lineage of crown gnathostomes, confirming both the pivotal position and themonophyly ofmaxillate placoderms.”

By contrast, in the LRT Qiilinyu (Fig 3) nests with a more similar jawless taxon, Poraspis (Fig 3, not mentioned in the text), marking the genesis of placoderms prior to the invention of an anteriorly curved moveable mandible in this clade of gnathostomes.

Remember, our ancestors developed jaws independent of placoderms, sharks and catfish, as documented in October 2023 here. This very recent news post-dates submission of the Cui et al manuscript and figures to the editors of Nature. So no one in academia knew this then.

Figure 3. Jawless Poraspis to scale with the related basal placoderm, Qilinyu. New tetrapod homology colors are applied here. At first glance, Qilinyu does resemble Entelognathus, but other taxa in the LRT are more similar to each one, separating them from each other phylogenetically.

Cui et al reported,
“Our analysis generated 100,000 trees,” which was their ‘maximum trees in memory’ limit. When this happens, something (usually scoring), is wrong, based on 25 years of experience. Go back and review your scores and get rid of taxa based on scraps.

Entelognathus primordialis
(Zhu et al. 2013; Zhu et al 2016, Cui et al 2023; Late Ludlow, Late Silurian, 419 mya; IVPP V18620) is a genus of placoderm fish with tiny eyes. Here (Fig 4) skull bones are re-identified with their tetrapod homologies. Pre-teeth are tiny pustules and wrinkles on the bone. Only a few days ago we looked at the scooping mouth of Entelognathus.

Documenting the back half of Entelognathus is welcome news.
The heavy scalation comes as no surprise to the LRT which was expecting that based on the similar traits found in related taxa (= phylogenetic bracketing, Fig 1 ). It is also important to keep working on your cladogram if it keeps recovering the maximum limit of trees (see above). Add taxa and re-check your scores. Ideally a single, fully-resolved tree should be your goal (if you can avoid using taxa based on scraps).

References
Cui X-D, Friedman M, Yu Y, Zhu Y-A and Zhu M 2023. Bony-fish-like scales in a Silurian maxillate placoderm. Nature Communications doi.org/10.1038/s41467-023-43557-9
Zhu M, Yu X-B, Ahlberg PE, Choo B and 8 others 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 502:188–193.
Zhu M et al. 2016. A Silurian maxillate placoderm illuminates jaw evolution. Science 354.6310 (2016): 334-336.

wiki/Entelognathus

A new scooping mouth tip for the small-eyed placoderm, Entelognathus

A postfrontal looking and acting exactly like a hyomandibular

I was walking around with a cartoon question mark over my head
for the longest time whenever I studied Jagorina (Fig 2) and Gemuendina (Fig 3), two ray-like traditional placoderms. I wondered, ‘what were the transitional taxa that connected them with more traditional placoderms?’ It seemed they tended to stand apart from all the others.

In evolution no taxon should ever stand alone or apart.

Once again,
it took a plesiomorphic Bauplan to understand an otherwise cryptic derived taxon. This time the largely traditional, but notably ultrawide-skull placoderms, Stenosteus (Fig 2) and Titanicthys (Fig 1) provided that transitional Bauplan. Both seem to have been weak-jawed bottom feeders sifting and filtering quantities of sand for randomly buried prey items.

Figure 1. Late Devonian Titanichthys compared to scale with Late Silurian Entelognathus. See figure 2 for more closely related taxa. Note the large red quadrate, the jaw joint, and its relationship to the jaw joint anchor, the hyomandibular (dark green), a bone that started externally, but soon moved internally to do its job.

Starting with Titanichthys
(Fig 1) note the proximity of the postfrontal (orange) to the fused postorbital-preoperuclar-lacrimal (amber-light yellow-tan) compared to the more posterior hyomandibular (dark green in Fig 1). Also note the medial connection of the postfrontal to the two small skull bones, the intertemporal and supratemporal (yellow-green and green).

In almost all gnathostomes the hyomandibular connects to the jaw joint (the red quadrate) with an internal process (not shown here).

If you’re looking for teeth, these taxa probable had a premaxilla pasted beneath the tiny nasals, but the maxilla had not yet appeared.

Figure 2. Jagorina (left) and Stenosteus (right). Colors added here. Note the fusion of the parietals, the loss of the frontals and nasals and the connection of the bar-like postfrontal to the fused preorbital-preopercular-lacrimal in Jagornia. That same connection is not made in Stenosteus, which has a more primitive skull. The postfrontal was identified here based on its geographic relationship with other bones, not by what it does in this case, which is different from nearly all other vertebrates.

Compare the Titanichthys setup with the similar, but different elements
in the more derived wide-skull of Jagornia (Fig 2 left). Also compare Titanichthys (Fig 1) to the more primitive Stenosteus (Fig 2 right), which is narrower and closer to Coccosteus Fig 2 lower right corner. In Jagornia we see the fusion of the parietal elements, the loss of the frontals + nasals and the retained connection of the now bar-like postfrontal to the fused preorbital-preopercular-lacrimal, now also reduced to a curved bar forming the palate.

The same postfrontal connection is made in Gemuendina (Fig 3), a ray-like relative of Jagorina. The quadrate (red) is reduced to a vestige in both. The hyomandibular remains a broad surface plate in both alongside the tabulars (light red).

Figure 3. The ray-like placoderm Gemuendina skull in situ. Colors added here. Compare to Jagorina in figure 2. Note the plate-like hyomandibular (dark green) not associated with the mandible, which is anchored here by the postfrontal (orange).

Now that the cartoon question mark over my head has popped,
and the (hypothetical) solution is shared, it’s worthwhile to really appreciate the prevalence of convergence in vertebrates. Problems like this, especially when not recognized, lead to incorrect scoring in phylogenetic analysis. This is why the fish subset of the LRT is taking so long to complete. Hope this helps in your own studies.

If this is already taught at the uiniversity level, let me know.

Evolution and synonyms of the hyomandibular and intertemporal

Five fat, flat basal gnathostomes compared

Sometimes it is worthwhile
to gather together and compare related taxa in one image so we can more clearly see and appreciate both the subtle and obvious traits and proportions that lump and separate them in analysis. These taxa (Fig 1) are all basal gnathostomes close to or within traditional placoderms in the LRT. We looked at each one earlier. Here they are collected together and updated letting one inform on another. None are larger than a human hand. Some are as small as a finger.

This is a difficult bunch. The original authors assigned several to lobe fin clades.

Figure 1. Bianchengichthys, Miguashaia, Dialipina and Guiyu in situ and reconstructed using DGS methods. In the LRT these four nest close to one another. Note the fuzzy-tipped posterior fins in the top three taxa along with the armored pectoral fins sporadically preserved. Also note the lack of any internal vertebrae in the bottom two taxa, both opened up by similar a ‘bite mark’, in contrast to Dialipina. Also note the transformation of the carapace into a dorsal spine in the bottom three taxa, displaced to the tail in Dialpina.

The fifth flat, fat basal gnathostome,
Early Devonian Drepanaspis (Fig 2), is re-presented here with more attention to detail and revised DGS colors based on the Bauplan of Bianchengichthys (top image Fig 1). Drepanaspis lacks a thoracic shield, but has a heavily scaled thorax and tail, as in Middle Devonian Miguashaia, Early Devonian Dialipina and Late Silurian Guiyu (Fig 1). Under closer examination with Bianchengichthys and the other three taxa (Fig 1) as my new guides:

Here in Drepanaspis nares are identified atop the nasals, as in Bianchengichthys.

Here a premaxilla (yellow) with tiny teeth is revealed beneath a broken piece of nasal.

Here a tiny vestige of a quadrate (red) is located anterior to the tiny orbit notch.

Here the former caudal fin is reinterpreted as a dorsal fin appearing prior to what appears to be a broken off caudal fin, creating a sort of double caudal fin.

Figure 2. Drepanaspis, is presented here with more attention to detail and revised DGS colors.

If you know of another published interpretation of these five taxa
with as much attention to detail, let us all know in the comments. Mistakes will be corrected.

Once again
having a good Bauplan (Fig 1) really helps to understand difficult taxa (Fig 2) ~ one more reason to keep adding taxa to your own analysis and studies. Each one informs on the other, especially in the most difficult taxa.

YouTube’s Raptor Chatter takes on Longisquama

Video here:

Response here:
As someone who has personally examined Longisquama (Fig 1), added it to three previously published phylogenetic analyses and had a manuscript peer-reviewed and published in Rivista Italiana (Peters 2000), I can tell you that Longisquama is more completely preserved than indicated in your video. It is a lepidosaur (like Huehuecuetzpalli) and a tiny tanystropheid (like Sharovipteryx, Cosesaurus and Langobardisaurus). It is also the current proximal outgroup taxon to the Pterosauria (like Bergamodactylus), but it was evolving in its own direction, as a plumed bipedal sprinter (proportions like Sharovipteryx). Think of Longisquama as a Triassic frillneck lizard (Chlamydosaurus). The plumes were not paired. There was no mandibular fenestra.

Figure 1. Flapping Longisquama with the acme of plume development in this clade.

Longisquama had pycnofibers and a sternal complex (clavicles + interclavicle + single sternum, as in pterosaurs and just assembling itself in Cosesaurus). It also had a slender scapula and a stem-like, locked-down coracoid (as in pterosaurs, Sharovipteryx and Cosesaurus… and birds). This means it was flapping without flying. So it was a real active and flamboyant spectacle during mating rituals. Pre-pterosaurs emphasized their flapping wings during these rituals, so their wings grew larger. Longisquama emphasized its dorsal frills (also present in Cosesaurus), so its wings did not grow larger. Nevertheless, the fourth manual digit in Longisquama’s small hand was much longer than the other digits, and fibers trailed the forelimbs (as in Cosesaurus and pterosaurs). So Longisquama had small foldable ‘wings’, able to flap only (not fly) for mating rituals.

Longisquama had an antorbital fenestra (as in Cosesaurus, Sharovipteryx and pterosaurs) and the back teeth were multicusped (as in Bergamodactylus). One of the misinterpreted plumes, the one that goes off at an odd angle, is a leg. The feet are both present (twisted back atop the backbone at the base of the plumes) and a simple hinge ankle is present (as in Cosesaurus, Sharovipteryx and pterosaurs).

Figure 2. Click to enlarge. New tracings of Longsiquama (B) soft tissues and (C) bones.

It is unfortunate that this information has been kept under wraps, despite peer review publication over twenty years ago. Part of the blame goes to professor Mike Benton who writes textbooks that continue the myth that pterosaurs are archosaurs close to dinosaurs. Remember: a long finger four, a long toe five, and an interclavicle are never found in archosaurs. In 1999 Benton promoted Scleromochlus as a pterosaur and dinosaur ancestor, so you could imagine how he felt when a year later a paper came out that said his conclusions were false due to taxon exclusion.

Google: “Cosesaurus aviceps, Sharovipteryx mirabilis and Longisquama insignis Reinterpreted” and “A Reexamination of four proclacertiforms with implications for pterosaur phylogenesis” for more information on Longisquama. Google: “Timeline of pterosaur origin studies” for more information on the suppression of Longisquama research when dealing with pterosaur origins.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E. Buffetaut & D.W.E. Hone (eds.), Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica doi: 10.4202/app.2009.0145 online pdf
Jones TD et al 2000. Nonavian Feathers in a Late Triassic Archosaur. Science 288 (5474): 2202–2205. doi:10.1126/science.288.5474.2202. PMID 10864867.
Martin LD 2004. A basal archosaurian origin for birds. Acta Zoologica Sinica 50(6): 978-990.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277-301.
Peters D unpublished. Cosesaurus aviceps, Sharovipteryx mirabilis and Longisquama insignis Reinterpreted
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, DeKalb, IL, 1-279.
Senter P 2004. Phylogeny of Drepanosauridae (Reptilia: Diapsida) Journal of Systematic Palaeontology 2(3): 257-268.
Sharov AG 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologiceskij Zurnal (1): 127–130.

reptileevolution.com/longisquama.htm
wiki/Longisquama
researchgate.net/A_Reexamination_of_four_proclacertiforms_with_implications_for_pterosaur_phylogenesis
researchgate.net/Cosesaurus_aviceps_Sharovipteryx_mirabilis_and_Longisquama_insignis_Reinterpreted

A new scooping mouth tip for the small-eyed placoderm, Entelognathus

Late Silurian Entelognathus is distinctly different from
classic arthrodire placoderms, like Coccosteus and its large-eyed kin. Instead Entelognathus (Fig 1) has tiny eyes, so it was not a sight predator. Nor did it have sharp jaws. More likely it was a shallow water benthic (= sea floor) feeder, like a modern catfish.

Taking another look at the palate view of Entelognathus (Fig 1) revealed overlooked paired elements inside the palate (cyan) that matched the broken jaw tips when cut and pasted using DGS colors and a GIF reconstruction.

Figure 1. Entelognathus has a taphonomically distorted skull. Using DGS the elements are straightened out and a previously overlooked pair of jaw tips (cyan) are added.

Entelognathus could not be unique
in having relatively small eyes and a scooping lower jaw. So I went looking for other similar taxa.

Figure 2. Late Devonian Titanichthys compared to scale with Late Silurian Entelognathus. See figure 3.

Giant Middle Devonian Titanichthys
(Fig 2) and tiny Late Silurian Bianchengichthys (Fig 3) are two such small-eyed placoderms. Both had flattened, sand scooping transverse mandibles.

I finally realized that hole in the skull of Titanichthys (Fig 2) must be where the otherwise missing intertemporal and supratemporal bones were once located. So they are replaced here.

Figure 3. Late Silurian Entelognathus to scale with the much smaller and more primitive Late Silurian Bianchengichthys, both basal placoderms.

Readers might remember the pre-gnathostome, Qilinyu,
had a transverse ventral mandible that rotated, if at all, like a rope held taut. It provided no gape. By contrast, the arched mandible of Bianchengichthys (Fig 3) permitted a wide gape due to its curved geometry and placement at the margin of the wide rostrum. That big arc on those little jaws made all the difference between the two taxa.

Figure 4. Another bottom feeder, Guiyu, has a little proecting tip on its dentary.

Where else have we seen that little scoop at the jaw tips
of Entelognathus (Fig 1) and Titanicthys (Fig 2)? Once in the armored catfish, Hoplosternum, and again in the walking catfish, Clarias. Whenever placoderms get mentioned, these two extant catfish keep entering the conversation. We also see it in Late Silurian Guiyu (Fig 4), which evolved heavy interlocking scales in place of the former solid sheets of placoderm thoracic armor.

Entelognathus primordialis
(Zhu et al. 2013; Zhu et al 2016, Late Ludlow, Late Silurian, 419 mya; IVPP V18620) is a genus of placoderm fish with tiny eyes. Here skull bones are re-identified with their tetrapod homologies. Pre-teeth begin here as tiny pustules and wrinkles on the bone.

References
Zhu M, Yu X-B, Ahlberg PE, Choo B and 8 others 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 502:188–193.
Zhu M et al 2016. A Silurian maxillate placoderm illuminates jaw evolution. Science 354.6310 (2016): 334-336.

wiki/Entelognathus

Tiny Triassic Boreosomus and its larger Early Jurassic descendants

Again,
once the solution comes about it appears obvious. When you start to analyze fish you’ll find yourself becoming more familiar with the hundreds of tested fish taxa the more they are studied.

Figure 1. Boreosomus, Pachycormus, Euthynotus and Ohmdenia are related to one another in the LRT, here 3 of 4 of them are shown to scale. Currently this is the sister clade to the Porolepiformes, which gave rise to lungfish and tetrapods.

This time
tiny, speedy, streamlined Boreosomus (Fig 1) from Triassic Spitzbergen to Madagascar gives rise to a larger taxon attributed to Early Jurassic Pachycormus (BRLSI M1332, Fig 1), then Early Jurassic Euthynotus (Fig 1) and finally the rather large but left scattered in situ, Early Jurassic Ohmdenia (Fig 1) shown here reduced relative to the others in order to get more than just the nose in.

Boreosomus arcticus
(aka Diaphorognathus, Woodward 1912; Priem 1924; Early Triassic; 250 mya, 10-20cm) nests with two pachycormids including Ohmdenia. Note the procumbent dentary teeth and small anterior dorsal fin.

References
Cawley JJ, Kriwet J, Kug S and Benton MJ 2019. The stem group teleost Pachycormus (Pachycormiformes: Pachycormidae) from the Upper Lias (Lower Jurassic) of Strawberry Bank, UK. PalZ 93(2):285–302.
Hauff B 1953. Ohmdenia multidentata nov. gen. et nov. sp. Ein neuer grober Fischfund aus den Posidonienschiefern des Lias e von Ohmden/Holzmaden in Wü rttemburg. Neues Jahrb. Geol. P.-A. 97, 39–50.
Priem F 1924. Paleontologie de Madagascar. XII. Les Poissons fossiles. Ann. Paleont., vol. 13: 105–132.
Woodward AS 1912. Notes on some fish-remains from the Lower Trias of Spitzbergen. Bulletin of the Geological Institution of the University of Upsala 11:291-297.

wiki/Ohmdenia
wiki/Pachycormus
wiki/Boreosomus

Saurichthys and Yelangichthys revisited

Fang and Wu 2022 pulled together
many congeneric and other close relatives of the traditionally enigmatic ‘living torpedo’ of the Triassic, Saurichthys (Fig 1). That data enabled more scoring on Yelangichthys (Fig 2) which was previously scored on a skull lacking lateral facial bones, here restored based on a congeneric specimen (Fig 1).

Figure 2. The genus Saurichthys and kin to scale and about full size on 72-dpi monitors chiefly from Fang and Wu 2022 and scaled here. Luganoia and Saurichthys minimahleri added here.

According to Argyriou et al 2018,
“Their exact phylogenetic position is uncertain, though it is agreed that they are not members of Neopterygii. Historically, they have been seen as close relatives of the Acipenseriformes (which includes living sturgeon and paddlefish) as part of the Chondrostei, though this has been strongly questioned by modern studies, which suggests that it may lie outside the Actinopterygii crown group.”

Figure 2. More data on Yelangichthys informs the missing pieces from the prior data on this genus, now nesting with Saurichthys in the LRT.

According to Fang and Wu 2022,
“Saurichthyidae (Saurichthyiformes) have been resolved variously as the sister group to Acipenseriformes (sturgeons and their fossil relatives) (Xu et al. 2014) or Birgeriidae (Argyriou et al. 2018), as a stem chondrostean (Ren et al. 2021), or even a stem neopterygian lineage (Giles et al. 2017).”

Figure 3. The skull(s) of Sauricthys compared at scale to Luganoia and another related taxon, Semionotus. All three are Triassic fish.

Apparently, no one else
has yet tested tiny Luganoia as a proximal outgroup to the Saurichthys clade (Fig 1) and the Actinista (= coelacanths) where they all nest together in the large reptile tree (LRT, 2306 taxa). According to the LRT coelacanths are not related to other lobefins. They developed those lobe fins independently.

References
Argyriou T et al (5 co-authors) 2018. “Internal cranial anatomy of Early Triassic species of †Saurichthys (Actinopterygii: †Saurichthyiformes): implications for the phylogenetic placement of †saurichthyiforms”. BMC Evolutionary Biology. 18 (1): 161.
Fang G-Y and Wu F-X 2022. The predatory fish Saurichthys reflects a complex underwater ecosystem of the Late Triassic Junggar Basin, Xinjiang, China. Historical Biology
https://doi.org 10.1080/08912963.2022.2098023
Wu F, Chang M-m, Sun Yand Xu G 2013. A New Saurichthyiform (Actinopterygii) with a Crushing Feeding Mechanism from the Middle Triassic of Guizhou (China). PLoS ONE 8(12): e81010. doi:10.1371/journal.pone.0081010
Wu F-X, Sun Y-L and Fang G-Y 2018. A new species of Saurichthys from the Middle Triassic (Anisian) of Southwestern China. Vertebrata PalAsiatica 56(4):287–294. pdf

wiki/Luganoia
wiki/Saurichthys
wiki/Yelangichthys

Other than that set of giant teeth, these two taxa resemble one another

More work needs to be done on the LRT,
but this current pairing of time-separated extinct fish seemed worth sharing.

Not the origin of the preopercular (Fig 1, light yellow) in this clade from a larger cheek cover in tiny toothless and unnamed ANU V244 from the Early Devonian that breaks into three parts in larger toothier Calamopleurus from the Early Cretaceous.

At the same time, note the genesis of the jugal (cyan) splitting and expanding to form a tripartite operculum in just a few hundred million years.

Figure 1. The tiny unnnamed genus (ANU V244) from the Early Devonian compared to the much larger Cretaceous predator, Calamopleurus. Note the extreme width of the skull in both along with the large coverage of the postorbital (light yellow) covering most of the cheek. The former is virtually toothless, the later is blessed with long, sharp teeth. Note also the expansion and splitting of the jugal to form a three-part operculum, convergent with several other fish clades.

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

wiki/Calamopleurus

New paper on oldest bats cherry-picks the wrong outgroup taxa

Rietbergen et al 2023 reported,
“Here, we describe a new species of Icaronycteris based on two articulated skeletons discovered in the American Fossil Quarry northwest of Kemmerer, Wyoming. The relative stratigraphic position of these fossils indicates that they are the oldest bat skeletons recovered to date anywhere in the world.”

Remember: ‘oldest’ does not mean ‘most primitive.’

Figure 1. Icaronycteris gunnelli (ROM:Palaeobiology-Vertebrate Fossils:52666). One of the oldest bat fossils in the world.

We’ve seen this fossil before.
I based my drawing of Icaronycteris for ReptileEvolution.com on it in 2015 (Fig 2).

Figure 2. Icaronycteris reconstruction from several years ago based on the fossil in figure 1.

Not sure why bat experts continue to do this, but
the authors of this paper cherry-picked two bat outgroup taxa not related to bats: Erinaceus, the hedgehog, and Sorex, the shrew. This is a university tradition that needs to go away.

Whale experts do this, too, nesting extinct deer, cattle and pigs basal to whales and odontocetes basal to mysticetes.

Pterosaur experts do this, too, nesting phytosaurs, Euparkeria, Lagerpeton and/or Scleromochlus as outgroup taxa… anything to avoid considering Cosesaurus.

By contrast,
the large reptile tree (LRT, 2306 taxa, subset Fig 3) documents bat outgroup taxa back to Cambrian worms. The LRT nests the tiny ‘primate’ Microcebus at the base of the Chiroptera (the bat clade). Strangely, there was no mention of extant Tadarida in the text of Rietbergen et al 2023, nor does it appear in their cladogram.

BTW: The Green River bat 2022 in the LRT (Fig 3) is still unpublished.

Figure 3. Subset of the LRT focusing on bats and their ancestor, Microcebus, a mouse lemur.

Taxon exclusion continues at the end of 2023
as the number one problem facing paleontology. Never cherry-pick your outgroup taxa. Always let your wide-gamut cladogram pick for you. This is something you should be hearing from a PhD professor, not a home-schooled amateur blogger.

References
Rietbergen TB, van den Hoek Ostende LW, Aase A, Jones MF, Medeiros ED, Simmons NB 2023. The oldest known bat skeletons and their implications for Eocene chiropteran diversification. PLoS ONE 18(4): e0283505. https://doi.org/10.1371/journal.pone.0283505

reptileevolution.com/icaronycteris
wiki/Icaronycteris

A third convergent origin of branchials (throat bones)

Overlooked earlier,
but worth observing and considering. Let’s talk about placoderm branchials.

Figure 1. Coccosteus, Romundina and Campbellodus to scale. Compare to Cheirodus, Eurynotus, Bobasatrina and Platysomus below. DGS colors added here. Note the emergence of proto-branchials (magenta) in Campbellodus.

Branchials
(= largely parallel strips of bone developing beneath the jaws that help expand the throat) also developed in late-surviving discoidal placoderms, like Eurynotus (Fig 2) and Cheirodus (Fig 3).

Figure 2. Eurynotus nests between Campbellodus nd Cheirodus in the LRT. Note the appearance of branchials (magenta), as in Cheirodus in figure 3.

Here we can see the initial breakup
of the once solid ventral plate extending anteriorly from the plastron of Romundina (Fig 1) and Campbellodus (Fig 1) as it splits apart forming rather typical and convergent branchials in Eurynotus (Fig 2) and Cheirodus (Fig 3).

Figure 3. Cheirodus nests as a late-surviving placoderm in the LRT. DGS colors are updated here.

Earlier
Cheirodus and Eurynotus entered the placoderm clade. That hypothesis of interrelationships remains untested, unconfirmed, unrefuted and unmodified. Expand your own taxon list to test this hypothesis. Let us know what you get.

Four late-surviving placoderms convergent with bony fish: Eurynotus, Bobasatrania, Cheirodus and Platysomus