New Scleromochlus/pterosauromorph paper excludes tested pterosaur ancestors

Foffa et al 2022 reports,
“Pterosaurs, the first vertebrates to evolve powered flight, were key components of Mesozoic terrestrial ecosystems from their sudden appearance in the Late Triassic until their demise at the end of the Cretaceous. However, the origin and early evolution of pterosaurs are poorly understood owing to a substantial stratigraphic and morphological gap between these reptiles and their closest relatives, Lagerpetidae.

Lagerpetids are proterochampsid archosauriformes not related to pterosaurs in the large reptile tree (LRT, 2162 taxa).

“Scleromochlus taylori [Fig 1], a tiny reptile from the early Late Triassic of Scotland discovered over a century ago, was hypothesized to be a key taxon closely related to pterosaurs, but its poor preservation has limited previous studies and resulted in controversy over its phylogenetic position, with some even doubting its identification as an archosaur.

This is why vertebrate paleontologists need to build their own LRT. If you exclude pertinent taxa you will never find for yourself the origin of pterosaurs.

“Here we use microcomputed tomographic scans to provide the first accurate whole-skeletal reconstruction and a revised diagnosis of Scleromochlus, revealing new anatomical details that conclusively identify it as a close pterosaur relative within Pterosauromorpha (the lagerpetid + pterosaur clade).

Adding taxa invalidates the Foffa et al hypothesis of interrelationships.

“Scleromochlus is anatomically more similar to lagerpetids than to pterosaurs and retains numerous features that were probably present in very early diverging members of Avemetatarsalia (bird-line archosaurs). These results support the hypothesis that the first flying reptiles evolved from tiny, probably facultatively bipedal, cursorial ancestors“.

Scleromochlus IS closer to lagerpetids than pterosaurs in the LRT. And the first flying reptiles (e.g. Bergamodactylus) did evolve from tiny, bipedal cursorial ancestors.

Figure 1. Scleromochlus.

My reply to the Paleocast video (below) interview with lead author Foffa:
“A look through the citation list reveals a citation omission: Peters D 2000. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336. Scleromochlus has tiny hands and no pedal digit 5. Pterosaurs have large hands and a tanystropheid-like pedal digit 5 shared with Cosesaurus, Sharovipteryx, Longisquama and Langobardisaurus, the four taxa (see above) nesting closer to pterosaurs than any archosaur. Cosesaurus has a sternal complex (clavicles + interclavicle + sternum), pteroid and prepubis plus extradermal membranes trailing all four limbs, as in pterosaurs. Scleromochlus lacks these traits. Scleromochlus nests with basal bipedal crocodylomorphs when permitted to do so. Taxon exclusion is the number one problem facing paleontology. Details at ReptileEvolution dot com.”

Figure 2. Scleromochlus from Foffa et al 2022 sporting a longer, previously buried tail. Note the deep chevrons. Pterosaurs and their ancestors lack these.

Davide Foffa was kind enough to send a PDF while writing today’s blogpost.
Here’s my reply, ‘Thank you for the prompt and courteous reply to my PDF request. I also heard your Paleocast podcast.

You expressed an interest in finding pterosaur precursors. I was in your shoes in the late 1990s, just getting started writing papers (without a degree). In the following years several were published including:

Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.

That’s a citation missing from your reference list. In addition, a manuscript attempting to correct my freshman mistakes can be found here:

Since 2011 I have been building an online cladogram of 2160 vertebrates including Scleromochlus, pterosaurs and their precursors back to Ediacaran worms. I note that the four genera tested in the Rivista paper were omitted from your team’s taxon list. Taxon omission appears to be the number one problem in paleontology. For instance, Vancleavea nests with thalattosaurs when those taxa are included.

Pterosaur origin omissions are systematic, as chronicled here:

If you’re really interested in pterosaur ancestry, please go see Cosesaurus in Barcelona. I found it wrapped in toilet paper when it should have had a place of honor. Here’s a link to that taxon online: http://reptileevolution.com/cosesaurus.htm

I have also studied Sharovipteryx and Longisquama. You’ll find links to those two on the Cosesaurus web page and more data in the ResearchGate manuscript.

Here’s that large and growing larger cladogram that nests Lagerpeton with Tropidosuchus within the Proterochampsidae and Scleromochlus within the basal bipedal Crocodylomorpha. http://reptileevolution.com/reptile-tree.htm

I try to avoid incomplete taxa. Those are set aside in dark red on the cladogram and then omitted from the .nex file. I also show my data on the page of that website. So if there is a mistake, let me know.

The lack of a tanystropheid-like fifth toe was the first clue I had that Scleromochlus was not related to basal pterosaurs. The second clue was the tiny hand and digit four was not the longest. You’ll note that Cosesaurus, Sharovipteryx and Longisquama all have that odd fifth toe. They also increasingly emphasize manual digit 4 as taxa nest closer to pterosaurs. Cosesaurus has a prepubis and pteroid, a sternal complex (clavicles + interclavicles + sternum), an attenuated tail, uropatagia, an elongate ilium with 4-5 sacrals,  simple hinge ankle joint, an antorbital fenestra, etc. etc. None of these are found in archosaurs, but the last two by convergence.

Here’s a link to the origin of pterosaur wings from ancestral lepidosaurs: http://reptileevolution.com/pterosaur-wings.htm

It’s been a fascinating twenty-two years watching as colleagues I’ve interacted with at symposia have studiously avoided testing taxa presented so long ago in a peer-reviewed paper that resolved the origin of pterosaurs question.

Congratulations on getting your work published in Nature. It’s unfortunate that taxon omission ruined an otherwise laudable paper.

Let’s keep in touch. And let me know whenever I can help.

References
Foffa D et al (10 co-authors) 2022. Scleromochlus and the early evolution of Pterosauromorpha. Nature https://doi.org/10.1038/s41586-022-05284-x
Peters D 2000. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336.

Paleocast video interview of lead author Davide Foffa.

Do pterosaur tongue bones look like bird tongue bones?

You decide.
Here are images (Fig 1) from Li, Zhou and Clarke 2018 for you to compare.

Li, Zhou and Clarke 2018 wrote:
“Here, we bring together evidence from preserved hyoid elements from dinosaurs and outgroup archosaurs, including pterosaurs, with enhanced contrast x-ray computed tomography data from extant taxa. Midline ossification [= basihyoid] is a key component of the origin of an avian hyoid. The elaboration of the avian tongue includes the evolution of multiple novel midline hyoid bones and a larynx suspended caudal to these midline elements.

The myth that pterosaurs are archosaurs is supported only by systematic taxon exclusion. When you see cladogram borrowing and taxon exclusion like this, red flags should pop up. The authors are working from an invalid phylogenetic analysis. That means their conclusions are tainted to mistaken.

Phylogenetic analysis recovers Cosesaurus (Fig 2) as a lepidosaur pterosaur ancestor.

Figure 1. Image from Li, et al 2018. Simplified here. Pterosaur added here.
Figure 1. Image from Li, Zhou and Clarke 2018. Simplified here. Pterosaur (Ludodactylus) added here. Question: which tongue is most like the pterosaur tongue? The complex bird tongue? Or the simple tuatara tongue?

Li, Zhou and Clarke 2018 continued:
“While variable in dentition and skull shape, most bird-line archosaurs show a simple hyoid structure. Bony, or well-mineralized, hyoid structures in dinosaurs show limited modification in response to dietary shifts and across significant changes in body-size. In Dinosauria, at least one such narrow, midline element is variably mineralized in some basal paravian theropods.

That ‘midline element’ was labeled the basihyoid in Jiang, Li, Cheng and Wang 2020.

“Only in derived ornithischians, pterosaurs and birds is further significant hyoid elaboration recorded. Furthermore, only in the latter two taxa does the bony tongue structure include elongation of paired hyobranchial elements that have been associated in functional studies with hyolingual mobility.”

And that is why the word ‘convergent’ is in the authors’ headline. Thankfully the authors did not make the phylogenetic mistake of Mike Benton concerning dinosaur feathers and convergent pterosaur pycnofibers. But they did consider pterosaurs as archosaurs. Very bad.

Nowhere mentioned in the text:
The pterosaur precursor, Cosesaurus (Fig 2), likewise has gracile, bent Y-shaped hyoids. This taxon has been systematically excluded from pterosaur origin studies.

Figure 2. Cosesaurus nasal crest (in yellow).
Figure 2. Cosesaurus nasal crest (in yellow). Hyoids shown in green. It could flap, but could not fly.

Two years later…
Jiang, Li, Cheng and Wang 2020 wrote: “The new fossil material revealed a novel type of hyoid apparatus and demonstrations the first basihyal in pterosaurs, revealed the hyoid morphology previously unseen. The hyoids in pterosaurs have a trend to shorten relative to the length of skulls, indicating the diminished role in lingual transport of food from the non-pterodactyloids to the pterodactyloids. The new gallodactylid, Gladocephaloideus, represents one of the least effective lingual retractions in all pterosaurs. Based on the elongated ceratobranchials and shape of the retroarticular process, the function of the Y-shaped istiodactylid tongue is unlike that of chameleons but closer to that of scavenging crows, which is consistent with the interpretation of the scavenging behavior in pterosaurs. More fossil samples are needed for further study on the function of other hyoids.”

Li Zhiheng is a co-author on both papers.

References
Jiang S, Li Z, Cheng X and Wang X 2020. The first pterosaur basihyal, shedding light on the evolution and function of pterosaur hyoid aparatuses. PeerJ https://peerj.com/articles/8292/
Li Z, Zhou Z and Clarke JA 2018 Convergent evolution of a mobile bony tongue in flighted
dinosaurs and pterosaurs. PLoS ONE 13(6):e0198078. https://doi.org/10.1371/journal.
pone.0198078

.

Pampaphoneus biccai enters the TST: Carnivore? Or herbivore?

According to Cisnernos et al 2012,
Middle Permian South American Pampaphoneus (Fig 1) was a “member of the Anteosauridae, an early therapsid predator clade known only from the Middle Permian of Russia, Kazakhstan, China, and South Africa.”

After testing in the Therapsid Skull Tree (TST, 77 taxa) nests Pampaphoneus between Titanoponeus and two specimens of Anteosaurus slightly distinct from the topology recovered by Cisneros et al.

Figure 1. Pampaphoneus skull in three views.

According to Cisoneros et al
“The genus is characterized, among other features, by postorbital bosses, short, bulbous postcanines, and strongly recurved canines. Phylogenetic analysis indicates that the Brazilian dinocephalian occupies a middle position within the Anteosauridae, reinforcing the model of a global distribution for therapsids as early as the Guadalupian.”

Figure 2. Titanophoneus, Pampaphoneus and two specimens of Anteosaurus to scale.

These taxa radiated across Pangaea
from South America to the Russian Urals during the Middle Permian. They left no descendants.

Figure 3. The Therapsid Skull Tree brought up to date with colors for likely carnvores and herbivores. Pampaphoneus and kin nest among other herbivores.

Carnivore? Or herbivore?
Cisneros et al reported, “Anteosaurids were the carnivore lineage within Dinocephalia, including the South African Anteosaurus magnificus and the Russian Titanophoneus potens, which were the largest (∼6 m long) terrestrial predators of the Permian.”

Phylogenetic bracketing indicates Titanophoneus and its descendants nested within other clearly herbivorous therapsids. The cheek teeth of Pampaphoneus are blunt and egg-shaped. Perhaps members of this clade were more like other extant herbivorous with big teeth, like mesonychids and hippos.

References
Cisneros JC et al (5 co-authors) 2012. Carnivorous dinocephalian from the Middle Permian of Brazil and tetrapod dispersal in Pangaea. Proceedings of the National Academy of Sciences of the United States of America. 109 (5): 1584–1588.
www.pnas.org/cgi/doi/10.1073/pnas.1115975109

wiki/Pampaphoneus
wiki/Anteosaurus

Sespia: an oreodont with an antorbital fenestra

Sespia (Schultz and Falkenbach 1968, Late Oligocene, 25 mya, Fig 1) is a genus of four species (Fig 2) of basal oreodont in the large reptile tree (LRT, 2159 taxa). Genus members were cat-sized to goat-sized and known from thousands of specimens from California to Nebraska. Apparently few to none are close to complete.

Figure 1. Sespia ultima in several views from Schultz and Falkenbach 1968. Note the large antorbital fenestra (aof) here and in other species (Fig 2). Arrow points to the very loose jaws joint apparently not so loose in two other species (Fig 2). Note the very large tympanic bulla (dark yellow) and raised auditory meatus, as in extant horses (Fig 4) by convergence.

Sespia was allied with Leptauchenia
(Fig 3, Schultz and Falkenbach 1968). Leptauchenia has not yet been tested in the LRT.

From a recent master’s thesis:
“Consensus is, that the oreodonts were an early group of artiodactyls. Most evidence puts the oreodonts in the suborder Tylopoda (Wikipedia, 2012). The cranium proper of the oreodonts is similar to that of the llama and camel.”

Why rely on consensus? That indicates laziness, the inability or lack of interest in finding out for oneself by examining data, creating a matrix and recovering a cladogram. Relying n consensus indicates trust in what others are saying. That quickly turns into hearsay, then rumor then mythology. Try not to rely on consensus. Build your own LRT.

Figure 2. Four species of Sespia from Schultz and Falkenbac 1968. S californica is the smallest. Note the large canines in S ultima, indicating male. Compare to the female in figure 1.

In the LRT
oreodonts are not close to camels, nor do they nest within Artiodactyla. Rather they nest with Phenacodus, basal to mesonychids and hippos on one branch, Homalodotherium + Protypotherum and then artiodactyls on the other branch.

An antorbital fenestra is present.
That’s really odd for a mammal. Schultz and Falkenbach called it a nasal-facial vacuity. From their footnote: “The term “nasal-facial vacuity” is used to distinguish the area from a facial vacuity which does not invade the nasal bone and little, if any, of the frontal. The nasal-facial vacuity invades the maxilla, nasal, frontal, and lacrimal bones and also opens into the orbit through the usually solid anterior orbital wall.” And later in their text: “Also noteworthy is the large nasal-facial vacuity which extends posteriorly through the anterior wall of the orbit. This character is not present in other oreodonts, nor in mammals in general.”

So far, I haven’t found any hypotheses regarding the presence of this vacuity, but my first guess is a relationship with the raised orbit and raised external auditory meatus (= eye hole and ear hole). Because the eyes and nostrils were placed high on the head.

Figure 3. Leptauchenia decora in water and sand up to their sensory organs. Neither is appropriate. Likely it was just the larger jaw muscles needed for grazing teeth that migrated the sensory organs dorsally, as in convergent horses (figure 4).

According to Wikipedia,
“it was long assumed that Leptauchenia was an aquatic, or semi-aquatic animal.” In counterpoint, Prothero and Sanchez 2008 suggested leptauchenids were desert-dwellers. The high-placed eyes, nostrils and ears served to filter out sand while burrowing, or while digging themselves free of sand dunes since their fossils are found in sand dunes.” See figure 3 to see an illustration of three niche hypotheses. The third is proposed below.

Figure 1. Equus the extant horse.
Figure 4. Equus the extant horse with high-placed nose, eyes and ears.

In counter-counterpoint,
another animal with deep jaws below high-placed eyes and ears is the extant horse. Equus is another running herbivore with deeply rooted molars (compare to Sespia in figure 1). Perhaps it was the convegent need for larger jaw muscles in grazing leptauchenid oreodonts that was responsible for moving the sensory organs dorsally. Neither an aquatic nor a sand burrowing niche seems appropriate (Fig 3). Instead, like little horses, oreodonts appear to be running, grazing herbivores adapted to tough land plants filled with grit.

Figure 1. Pika skull (genus: Ochotona) in three views.
Figure 5. Pika skull (genus: Ochotona) in three views. Note a similar antorbital fenestra.

Why did an antorbital fenestra develop
in Sespia (Fig 1) and Leptauchenia, distinct from almost all other mammals? The extant pika (Ochotona, Fig 5) has something similar by convergence. All ideas are welcome.

References
Prothero DR and Sanchez F 2008. Systematics of the Leptaucheniine oreodonts (Mammalia: Artiodactylia) from the Oligocene and earliest Mioceneof North America. In: Lucas et al., eds., 2008, Neogene Mammals. New Mexico Museum of Natural History and Science Bulletin 44.
Schultz CB and Falkenbach CH 1968. The phylogeny of the oreodonts, Parts 1 and 2. Bulletin of the American Museum of Natural History 139:498pp.

wiki/Sespia
wiki/Leptauchenia
wiki/Merycoidodontoidea = Oreodonta

The earliest hylobatid (gibbon) from the Late Miocene of China

Ji et al. 2022 report,
“Yuanmoupithecus xiaoyuan, a small catarrhine from the Late Miocene of Yunnan in southern China, was initially suggested to be related to Miocene proconsuloids or dendropithecoids from East Africa, but subsequent reports indicated that it might be more closely related to hylobatids. Here, detailed comparisons of the material, including seven newly discovered teeth and a partial lower face of a juvenile individual, provide crucial evidence to help establish its phylogenetic relationships. Yuanmoupithecus exhibits a suite of synapomorphies that support a close phylogenetic relationship with extant hylobatids. Furthermore, based on the retention of several primitive features of the dentition, Yuanmoupithecus can be shown to be the sister taxon of crown hylobatids.

Yuanmoupithecus maxilla and cheek teeth.

Ji et al. 2022 continue:
“Currently then, Yuanmoupithecus represents the earliest known definitively identified hylobatid and the only member of the clade predating the Pleistocene. It extends the fossil record of hylobatids back to 7–8 Ma and fills a critical gap in the evolutionary history of hominoids that has up until now remained elusive. Even so, molecular estimates of a divergence date of hylobatids from other hominoids at about 17–22 Ma signifies that there is still a substantial gap in the fossil record of more than 10 million years that needs to be filled in order to document the biogeographic origins and early evolution of hylobatids.”

Figure 1. Earlier the LRT nested gibbons, rather than more chimp-like australopitheciens in the lineage of humans.

Based on molar sizes,
the authors estimate their Miocene gibbon weighed about six kilograms,the same as gibbons today. Molar structure indicates a gibbon-like fruit diet. Sahelanthropus (Fig 1) is from Chad (Africa) 7mya. Proconsul (Fig 1), from Kenya, is 2x-3x older.

References
Ji X et al (10 co-authors) 2022. The earliest hylobatid from the Late Miocene of China. Journal of Human Evolution 171:103251

Apternodus enters the LRT with Solenodon and Desmana

Apternodus baladontus (Matthew1903, Asher et al 2002; Eocene to Oligocene, 35mya, Fig 1) was traditionally considered a member of the Soricomorpha (= shrew-forms) within Insectivora a now abandoned clade. Here in the large reptile tree (LRT, 2158 taxa) Apternodus nests with Solenodon (Fig 2) and they nest with Desmana, a taxon not mentioned by Asher et al.

Figure 1. Apternodus skull from Asher et al 2002. Both sides of the same skull are shown. Colors added here. Don’t look for canines. This clade lacks them. Yes, five molars are present in Apternodus as in monotremes. That is a reversal from the traditional four, three or fewer molars in more primitive taxa.

Note the bulbous upper second premolar
and pavement-stone-like lower premolars on Apternodus. The jugals are tiny to absent. By contrast the squamosal is extra large.The top of the dentary coronoid process is unmiquely curled laterally. The lacrimal opening is quite large. In dorsal view the nasals meet the parietals in a narrow bridge, splitting the frontals.

Figure 2. Solenodon data used in the LRT. Note the four molars. Compare to Apternodus in figure 1.

Solenodon has the more primitive teeth,
but it survived to the present day. According to Wikipedia, “Oligocene North American genera, such as Apternodus, have been suggested as relatives of Solenodon, but the origins of the animal remain obscure.” So this interrelationship is not novel.

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.
Brandt JF von 1833. De Solenodonte, novo mammalium insectivorum genere. Mem. de l’Acad. de St. Petersbourg, II 1833:459-478.
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/Apternodus – not yet posted
wiki/Solenodon
wiki/Soricomorpha

Tiny Early Silurian Shenacanthus reconstructed and reidentified

This is a follow-up to
yesterday’s post on several tiny Early Silurian fish from China. Among the specimens was one plate and counterplate of tiny Shenacanthus vermiformis (Zhu et al 2022, Figs 1, 2).

Figure 1. Shenacanthus vermiformis images from Zhu et al 2022. Not a chondrichthyan, but an arthrodire placoderm, as suspected yesterday.
Figure 1. Shenacanthus vermiformis traced and reconstructed using DGS techniques. Colors added here.
Figure 1. Shenacanthus vermiformis traced and reconstructed using DGS techniques. Colors added here.

From the Zhu et al diagnosis:
“Small chondrichthyan, approximately 22 mm from the rostrum to the anal fin. Fusiform body shape; small cranium (~3.5 mm from the rostrum to the shoulder girdle) with blunt rostrum; dentition absent; branchial region posteriorly positioned in relation to the cranium; branchiostegal and hyoidean plates absent, shoulder girdle covered in large dermal plates both dorsally and ventrally, two median dorsal plates, the anterior one smaller and oblate, the posterior one larger and teardrop-shaped, with vermiform ornament; paddle-like pectoral fins lacking fin spine; Anal fin also lacking fin spine. Small, diamond-shaped scales. Small scutes or dermal plates with linear ornament along the dorsal and ventral midlines.”

The reconstruction (Fig 1) confirms an earlier suspicion that Shenacanthus was a tiny arthrodire placoderm, not a chondrichthyan (= sharks, rays and ratfish). Apparently the ‘dorsal spine’ is instead part of the dorsal shield. There is no anal fin. Claspers are identified here.

Figure 3. The iconic spiny shark, Climatius. Shown about 2x life size.

Zhu et al. nested Shenacanthus
between the spiny sharks Paucicanthus, Gladbachus, Climatius (Fig 3) and Doliodus + crown-group chondrichthyans in an unresolved clade. Taxon exclusion is a problem.

Gladbachus is an extinct whale shark.
Doliodus is a primitive deep-sea, big-mouth actinopterygian.
Spiny sharks are not chondrichthyans, but basal bony fish in the lobefin clade.

Figure 4. Early Silurian Shenacanthus demonstrates extreme phylogenetic miniaturization at the origin of arthrodire placoderms. That’s the headline here.

Here
in the large reptile tree (LRT, 2158 taxa) tiny Shenacanthus nested with tiny Millerosteus with such a similar trait list that these two are likely congeneric. Only size and time separate them. Millerosteus is not mentioned in the Zhu et al text. Their cladogram includes only a suprageneric clade ‘Arthrodira’.

This appears to be a novel hypothesis of interrelationships.

References
Zhu Y-A et al (10 co-authors) 2022. The oldest complete jawed vertebrates from the early Silurian of China. Nature 609:954–958. online

wiki/Shenacanthus – not yet posted

More tiny fish from the Early Silurian! No wonder they’ve been so hard to find.

Zhu et al 2022 report,
“Molecular studies suggest that the origin of jawed vertebrates was no later than the Late Ordovician period (around 450  million years ago.”

Unfortunately, Zhu et al did not realize placoderms (Fig 2) developed their own jaws and lateral fins by convergence with gnathostomes (Fig 1), according to the large reptile tree (LRT, 2157 taxa), which tests many more outgroup taxa omitted by others.

Figure 1. Origin of lateral fins and jaws in the gnathostome line.
Figure 1. Origin of lateral fins and jaws in the gnathostome line. Note how many late surviving taxa precede Haikouichthys preserved in Early Cambrian strata. This is heresy. Kalanaspis is a new addition. Not to scale.

Tiny Late Silurian Bianchengichthys,
(Fig 2) remains the most primitive known placoderm with jaws sans teeth. Similarly, large Early Jurassic Chondrosteus (Fig 1) remains the most primitive known gnathothostome with jaws sans teeth. The extant nurse shark, Ginglymostoma, and a tiny extinct nurse shark, Ramirosuarezia (Fig 8), are the most primitive tested taxa in the LRT with jaws + teeth.

Zhu et al continue:
“Together with disarticulated micro-remains of putative chondrichthyans from the Ordovician and early Silurian period, these analyses suggest an evolutionary proliferation of jawed vertebrates before, and immediately after, the end-Ordovician mass extinction. However, until now, the earliest complete fossils of jawed fishes for which a detailed reconstruction of their morphology was possible came from late Silurian assemblages (about 425 Ma).”

Figure 2. The origin of arthrodire placoderms to scale and full scale @ 72dpi. None of these have teeth per se, nor do they have a premaxilla, maxilla or dentary.

Zhu et al continue:
“The dearth of articulated, whole-body fossils from before the late Silurian has long rendered the earliest history of jawed vertebrates obscure.”

Sometimes extant taxa can provide all the data one needs as illuminated in the LRT.

Figure 3. Early Silurian Loganellia compared to extant Rhincodon (whale shark) pup.
Figure 3. Early Silurian Loganellia compared to extant Rhincodon (whale shark) pup. Both have jaws without teeth.

Zhu et al continue:
“Here we report a newly discovered Konservat-Lagerstätte, which is marked by the presence of diverse, well-preserved jawed fishes with complete bodies, from the early Silurian (Telychian age, around 436 mya) of Chongqing, South China.”

This was a wonderful discovery with several tiny fish on a small plot.

Figure 4. Xiushanosteus from Zhu et al 2022, Colors added here on second frame. Scale bars = 1cm. Shown 2x life size. Xiushanosteus nests in the LRT basal to Lunaspis + Shearsbyaspis.

Zhu et al continue:
The dominant species, a ‘placoderm’ or jawed stem gnathostome, which we name Xiushanosteus mirabilis gen. et sp. nov., combines characters from major placoderm subgroups and foreshadows the transformation of the skull roof pattern from the placoderm to the osteichthyan condition.”

Correction: the last common ancestor of placoderms and bony fish (= osteichthyans) was jawless, finless, unarmored Metaspriggina, a short-bodied, lamprey-like taxon (Fig 1).

Figure 5. Shenacanthus from Zhu et al 2022, and at full size on a 72dpi monitor. This appears to be a tiny arthrdire placoderm which had a mandible (not preserved) lacking teeth.

Zhu et al continue:
“The chondrichthyan Shenacanthus vermiformis gen. et sp. nov. exhibits extensive thoracic armour plates that were previously unknown in this lineage, and include a large median dorsal plate as in placoderms combined with a conventional chondrichthyan bauplan..”

Apparently Zhu et al mslabel Shenacanthus a ‘chondrichthyan’ because they misidentified a dorsal plate as a dorsal spine or this placoderm had a dorsal spine. Otherwise this is a typical tiny arthrodire placoderm smaller than Millerosteus (Fig 2).

Figure 6. The toothless Early Silurian galeapsid, Tujiaaspis.

“Together, these species reveal a previously unseen diversification of jawed vertebrates in the early Silurian, and provide detailed insights into the whole-body morphology of the jawed vertebrates of this period.”

According to interviews at upi.com Science_News:
Gai Zhikun said Tujiaaspis fossils (Fig 6) revealed “that these animals possessed paired fins that extended continuously, all the way from the back of the head to the very tip of the tail. This is a great surprise since galeaspids have been thought to lack paired fins altogether.”

You can see what was known of galeaspids prior to this discovery on their ReptileEvolution.com page here.

Figure 6. Qianodus tooth whorls enlarged and shown full size on a 72dpi monitor.
Figure 7. Qianodus tooth whorls enlarged (below) and shown full size on a 72dpi monitor (above). These create science headlines in the era of the Internet.

The Early Silurian tooth whorl: Qianodus duplicis
Andreev et al 2022 reported, “Here we provide, to our knowledge, the earliest direct evidence for jawed vertebrates by describing Qianodus duplicis, a new genus and species of an early Silurian gnathostome based on isolated tooth whorls from Guizhou province, China. The whorls possess non-shedding teeth arranged in a pair of rows that demonstrate a number of features found in modern gnathostome groups. These include lingual addition of teeth in offset rows and maintenance of this patterning throughout whorl development. Our data extend the record of toothed gnathostomes by 14 million years from the late Silurian into the early Silurian (around 439 million years ago) and are important for documenting the initial diversification of vertebrates. Our analyses add to mounting fossil evidence that supports an earlier emergence of jawed vertebrates as part of the Great Ordovician Biodiversification Event (approximately 485–445 million years ago).”

This second paper also in the same issue of Nature
(Andreev et al 2022) sparked headlines worldwide for tiny spiral tooth whorls.

Meanwhile, back in the LRT Ramirosuarezia (Fig 8, Pradel, Maisey, Tafforeau and Janvier 2009) preserved tiny teeth and tiny skull in this Middle Devonian tiny nurse shark. Loganellia, the extinct whale shark with a carpet of teeth is also from the Early Silurian.

Co-author Zhu My was aware of Loganellia,
reporting in blazetrends.com, “among vertebrates there is a jawless minority group (the agnathians), but even “the oldest teeth of these jawless fish are pharyngeal denticles or tooth-like oral elements, Loganelia telodon (see Fig 3) from the Silurian of Scotland, about 425 million years ago”, he continues.”

Jawless minority? No.
Younger? Yes.
Complete preservation (not just a tooth?) Yes (Fig 3).
Modern relatives? Yes, but these are not mentioned to reporters.

Figure 8. Ramirosuarezia, a tiny Middle Devonian nurse shark, preserves teeth only laterally on the jaws.

Friedman 2022 provided some in-house publicity for this series of papers.
and he supports a single origin for jawed vertebrates. Strangely Friedman does not mention the sub-guppy size of many specimens.

References
Andreev PS (9 co-authors) 2022. The oldest gnathostome teeth. Nature 609:964–968. online.
Pradel A, Maisey JG, Tafforeau P and Janvier P 2009. An enigmatic gnathostome vertebrate skull from the Middle Devonian of Bolivia. Acta Zoologica (Stockholm) 90
(Suppl. 1):123–133.
Zhu Y-A et al (10 co-authors) 2022. The oldest complete jawed vertebrates from the early Silurian of China. Nature 609:954–958. online

Nature’s In-house Publicity
Friedman M 2022. Fossils reveal the deep roots of jawed vertebrates. Nature News&Views 609:897–898.

Publicity
for all the above taxa focused on the tiny tooth whorl (genus: Qianodus, Fig 7), which was promoted as the oldest vertebrate teeth (sans the rest of the anatomy) ever discovered. Published illustrations rarely if ever provided a sense of their tiny size. Just the opposite. Google search: Qianodus publicity

heurekalert.org/news-releases/966129
hsmithsonianmag.com/science-nature/haul-of-fossil-fish-pushes-back-the-origin-of-teeth-and-jaws-180980849/
upi.com/Science_News/2022/09/28/fossils-galeaaspids-fins-arms-legs/
blazetrends.com/an-ancient-shark-from-china-is-our-oldest-jawed-ancestor/?utm_source=rss&utm_medium=rss&utm_campaign=an-ancient-shark-from-china-is-our-oldest-jawed-ancestor

Nectocaris: chordate or squid? Or transitional from one to another?

Back to enigmatic invertebrates today.
Let’s take a look at Middle Cambrian Nectocaris (Figs 1–3, Morris 1976 ), known from a single specimen for a long time. Now it is known from 90 additional specimens.

Figure 1. Nectocaris pteryx illustration, lacking segmentation (see figure 2).

Smith and Caron 2010 wrote:
“Nautiloids, traditionally considered basal within the cephalopods, are generally depicted as evolving from a creeping Cambrian ancestor whose dorsal shell afforded protection and buoyancy. Although nautiloid-like shells occur from the Late Cambrian onwards, the fossil record provides little constraint on this model, or indeed on the early evolution of cephalopods. Here, we reinterpret the problematic Middle Cambrian animal Nectocaris pteryx as a primitive (that is, stem-group), non-mineralized cephalopod, based on new material from the Burgess Shale. This clade extends the cephalopods’ fossil record by over 30 million years, and indicates that primitive cephalopods lacked a mineralized shell, were hyperbenthic [= above the sea floor], and were presumably carnivorous. The presence of a funnel suggests that jet propulsion evolved in cephalopods before the acquisition of a shell. The explosive diversification of mineralized cephalopods in the Ordovician may have an understated Cambrian ‘fuse’.”

Figure 2. Nectocaris from Smith 2013, layered and colored here. Note the fins are supported by rays. The central organs are finely subdivided into segments corresponding to the rays.

Earlier,
in 1988 Alberto Simonetta wondered, “Is Nectocaris pteryx a chordate?,” based on the single original specimen. Smith and Caron 2010 did not address that hypothesis, but did cite that paper.

Figure 3. From Smith 2013. Colors added here.

I sent the following email to Dr. Martin Smith, Ontario, Canada,
author and co-author of several Nectocaris papers (cited below).

Dear Dr Smith:
Thank you for publishing on Nectocaris.

I took the liberty of apply colors to the head and funnel region of one of your closeup images of Nectocaris. See attached. It appears to follow an earlier hypothesis of a chordate origin for cephalopods. Here the notochord is the cuttlebone. The long twin ‘tentacles’ are not mouth parts, but sensory structures, as in hagfish, which also evert their mouth parts during feeding. This could be a variation on that Bauplan.
Your thoughts?
Best regards,

Figure x. Nematodes and hagfish side-by-side, focusing on the eversible mouth parts and keratin teeth.
Figure 4. Nematodes and hagfish side-by-side, focusing on the eversible mouth parts and keratin teeth.

Longtime readers might remember
an earlier hypothesis presented here linking lancelets (Branchiostoma) with nautiloids (Nautilus, Fig 5) and a cladogram that linked hagfish (Myxine) with Nautilus (Fig 6). Among other traits, the presence of large eyes (below the skin in extant hagfish) was a cephalopod synapomorphy not shared with blind lancelets.

Figure 5. A lancelet and nautilus compared from July 2021.

Getting back to chordates, Simonetta 1988 wrote,
“A revision of the morphology of Nectocaris pteryx Conway Morris, 1976, and a comparison with the morphology of living Chordates supports the inclusion of Nectocaris in the phylum Chordata. The supposed somewhat crustacean‐like valves, which sheath the forepart of the animal are probably better considered as being the dermo‐epidermal folds that limit the peribranchial cavity of most lower Chordates, while the tail closely resembles the tail of the larval Tunicata and of Branchiostoma. The large eyes are a unique feature.”

An affinity with hagfish is perhaps more appropriate given the new data from dozens of other specimens. That’s where Nautilus nested here back in July 2021.

Figure 6. Cladogram from July 2021 nesting Nautilus with Myxine, the hagfish.

Here’s a problem worth noting.
Hagfish swim like lancelets and fish: with vertical tail fins and lateral undulations. By contrast shell-less cephalopods, like squids, do not undulate the torso and swim by undulating horizontal fins, as in Nectocaris (Figs 1, 2).

Simmonetta interpreted the original (holotype) Nectocaris
with myomeres, vertical fins and a subterminal anus, as in lancelets and fish. That’s not the case with the latter 90 specimens presented by Smith and Caron 2010 and Smith 2013, the ones under study here (Figs 1, 2). So, getting back to the vertical vs horizontal fin problem…

Figure 5. IFrom July 2021 diagramming hypothetical transitional taxa between the lancelet and nautilus. Lancelets bury their tail in sediment, perhaps encouraging the evolution of a U-shaped gut and funnel to eliminate the waste outside the burial tunnel.

The solution was presented here a year ago
in which a step-wise reduction in lateral undulation and a stiffening of the notochord (Fig 5 transition 1) ultimately evolving into an immobile cuttlebone (= siphuncle), whether a shell was present or not, or later lost. Thereafter, to increase mobility and stability, lateral fins developed de novo in Nectocaris – just as they did by convergence in armored placoderms and again by convergence in armored osteostracans (Hemicyclaspis) followed by less armored Thelodus and sturgeons. So fin orientation from hagfish to cephalopods is not an insurmountable problem.

References
Simonetta AM 1988. Is Nectocaris pteryx a chordate? Bollettino di Zoologia. 55 (1–2): 63–68.
Smith MR and Caron JB 2010. Primitive soft-bodied cephalopods from the Cambrian. Nature 465 (7297): 469–472.
Smith MR 2013. Nectocaridid ecology, diversity and affinity: Early origin of a cephalopod-like body plan”. Paleobiology. 39 (2): 291–321.
Smith MR 2019. An Ordovician nectocaridid hints at an endocochleate origin of Cephalopoda. Journal of Paleontology. 94: 64–69.

wiki/Nectocaris

Publicity
wired.com/2011/07/nectocaris-what-the-heck-is-this-thing/
“On May 27th, 2010 paleontologists Martin Smith and Jean-Bernard Caron announced that they had found a spectacular solution to one of the fossil record’s long-running mysteries. Since its description in 1976, the 505 million year old fossil Nectocaris pteryx from British Columbia’s famous Burgess Shale had vexed scientists. Known from a single specimen – appearing as little more than a smear on a rock slab – this creature seemed to be equal parts chordate and arthropod. No one could say what it was. Thanks to the discovery of nearly 100 additional specimens, however, this Cambrian oddball could finally be reexamined and its affinities resolved. In the pages of Nature, Smith and Caron presented Nectocaris as the early, Cambrian cousin of all other cephalopods, informally promoted as the ur-squid.”

nationalgeographic.com/science/article/nectocaris-mystery-fossil-was-actually-a-500-million-year-old-squid-relative https://zoologynews.wordpress.com/

External gills: first appearance, radiation, disappearance

Curiosity drove this blogpost.
Where did external gills first appear? How widespread are external gills?

According to Wilkipedia:
“External gills are exposed to the environment, rather than set inside the pharynx and covered by gill slits, as they are in most fishes. The respiratory organs are set on a frill of stalks protruding from the sides of an animal’s head.”

Figure 1. Hemidactylum scutatum larval amphibian. Note the several (3 tan gills per side) external gills, plus that blue one on the left.

The first chordates,
lancelets like Branchiostoma, have internal gills as juveniles and adults. Sturgeon and their larvae, like Acipenser, have internal gills.

Larvae of the banded houndshark
(Triakis) have poorly organized external gills (Fig 2) prior to hatching, still attached to their yolk sac.

Figure 2. External gills appear in taxa from sharks to amphibians.

According to NotesOnZoology.com:
“External gills, though rare in fishes, are found in some larval forms of lampreys, Polypterus (bichir) has one pair of external gills. Dipnoi (Lepidosireri) have four pairs of filamentous external gills attached to the outer edges of the branchial arches.”

Figure 3. Lamprey embryo. Arrow points to possible external gills. Still not sure. Larvae do not have external gills. They have seven shark-like tall gill slits. Adults reduce these gill slits to small circular openings.

Larval and neotonic adult amphibians,
like Hemidactylum scutatum (Fig 1) display the most commonly known examples of external gills. Larval fish close to the fin-to-finger transition also have external gills (Figs 2, 4). Examples include Polypterus (Fig 2), the extant Nile bichir with one large pair of external gills.

Figure 3. Polypterus adult and larval forms. 1 pair of external gills are present in the juvenile, completely absent in the adult. This may be the post primitive example of external gills. Phylogenetically this grade of taxa was present in the Early Devonian, perhaps Late Silurian.

Polypterus bichir
(Geoffroy Saint-Hilaire 1802) is the extant Nile bichir. Given that it breathes air and can walk on land, early scientists were unsure whether this was a fish or an amphibian, then later unsure whether this was a crossopterygian or an actinopterygian. Here it nests between the Early Devonian dipnomorph, Powichthys and the mid-Devonian tetrapodomorphs, the lobefins that eventually developed fingers and toes.

Stundi et al. 2019 reported,
“This type of gill is most commonly observed on the aquatic larva of most species of salamanders, lungfish, and bichirs (which have only one large pair), and are retained by neotenic adult salamanders and some species of adult lungfish. They are present on non-transforming salamander species, such as most members of the family Proteidae (the olm and mudpuppies) and the family Sirenidae, which naturally never metamorphose into an air-breathing form.”

“The embryos of frogs and caecilians also develop external gills at some point in their development, though these are either resorbed before or disappear shortly after hatching. Fossils of the distant relatives of modern amphibians, such as Branchiosaurus and Apateon, also show evidence of external gills.”

Figure 1. Apateon overall and the skull in palatal and dorsal views. This taxon nests between Doleserpeton and Gerobatrachus in the LRT.
Figure 4. Apateon overall and the skull in palatal and dorsal views.

“The external gills commonly consist of a single stalk (rami) protruding from a gill arch behind the head of the animal, above an associated gill slit. The stalk usually contains muscle tissue, and may be moved by the animal as a free appendage, in order to stir up stagnant water. The stalk is lined by many thinly walled filaments (fimbriae), containing the majority of blood vessels used in gas exchange. Animals usually have one external gill originating on each gill arch (except the hyoid), which leads to there being three pairs of external gills in salamanders, and four in the gilled larvae of lungfish.”

“Polypterid bichirs represent the earliest diverged living group of ray-finned (Actinopterygian) fishes and they are often referred to as the most relevant species for studying character states at the dichotomy of ray- and lobe-finned fishes.”

The large reptile tree (LRT, 2155 taxa) does not recover that relationship. Bichirs are not the earliest diverging living group of ray-finned fish in the LRT, but among the latest, just before the fin-to-finger transition.

“This places bichirs in a unique phylogenetic position among vertebrates, which can be exploited for evolutionary and developmental comparative studies. Adult bichirs possess several intriguing characteristics that have been associated with air-breathing during the transition from water to land, such as ventral paired lungs or spiracular openings on the head. Moreover, bichirs also share several key larval features with lungfishes or amphibians, such as cranial adhesive organs, and larval external gills.”

That’s because bichirs are closely related to taxa in the fin-to-finger set of transitional taxa in the LRT.

“The external gills of bichirs represent prominent adaptive structures, and constitute major breathing organs of their free-living embryos and early larvae. Strikingly, while external gills of amphibians and lungfishes derive from branchial arches as a rule, those of bichirs have historically been considered as unique hyoid arch derivatives due to their blood supply from the hyoid aortic arch. Importantly, the external gills of bichir embryos represent the first cranial structures to appear, emerging before the eyes or mouth are evident.”

References
Stundi J et al.(8 co-authors) 2019. Bichir external gills arise via heterochronic shift that accelerates hyoid arch development. eLife 8:e43531. https://doi.org/10.7554/eLife.43531

wiki/External_gills
NotesOnZoology.com