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. 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. 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 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 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/

Lancelets and Nautilus compared

Phylogenetic bracketing indicates the Nautilus siphuncle is a remnant notochord

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 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

Moqisaurus: a new basal squamate from the Early Cretaceous close to Liushusaurus

Dong et al 2019 described
a new basal squamate, Moqisaurus (Fig 1) “We report a new genus and species of fossil lizard, Moqisaurus pulchrum gen. et sp. nov., from the Early Cretaceous Moqi Fauna of eastern Inner Mongolia, China. The new lizard differs from other Late Jurassic and Early Cretaceous taxa in the combination of an interdigitated frontoparietal suture, paired frontals and parietals, absence of angular process on mandible, and relatively short limbs.”

Figure 1. Moquisaurus pulchrum skull. Compare to Liushusaurus in figure 2.

Moqisaurus pulchrum
(Dong, Wang and Evans 2022, Early Cretaceous) nests with Liushusaurus in the large reptile tree (LRT, 2155 taxa). The well-preserved pectoral girdle in the new lizard provides the earliest fossil record of a mesosternal fontanelle.

Figure 2. Basal squamates and outgroup taxa in the LRT. Here Euposaurus and Liushusaurus are basal members of Iguania, a basal clade of Scleroglossa. Calanguban and Scandensia are basal to Scleroglossa.

Here,
in in the LRT, Moqisaurus nests with Liushusaurus at the base of the clade Iguania. Calanguban (Fig 2) from the Crato formation of Brazil nests as the last common ancestor of all squamates and then over a dozen taxa go back to tiny Late Permian Lacertulus all nesting within the Protosquamata, apart from other lepidosaurs.

Figure 3. Taxa at the base of the Lepidosauria include Paliguana, Tridentinosaurus, Lanthanolania, Lacertulus, Gephyrosaurus, Megachirella, Lacertulus and Palaegama.

So lepidosaurs radiated all across Pangaea
from the Late Permian through the Early Cretaceous (Fig 3). Some became pterosaurs by the Late Triassic.

References
Dong L, Wang Y, Mou L, Zhang G and Evans SW 2019. A new Jurassic lizard from China in Steyer J.-S., Augé M. L. & Métais G. (eds), Memorial Jean-Claude Rage: A life of paleo-herpetologist. Geodiversitas 41 (16): 623-641. https://doi.org/10.5252/geodiversitas2019v41a16.
http://geodiversitas.com/41/16

Little Millerosteus enters the LRT basal to small to giant arthrodire placoderms

Here’s a graphic demonstrating a portion of the arthrodire placoderm subset
of taxa tested so far (Fig 1) in the large reptile tree (LRT, 2153 taxa).

The newest addition,
goldfish-sized Millerosteus (Fig 1), nests shortly after the origin of placoderm jaws in ultra-tiny Bianchengichthys (Fig 1) and before a long, but gradual size increase culminating in the giant iconic placoderm, Dunkleosteus (Fig 1).

Figure 1. Arthrodire placoderm evolution full size and to scale @ 72dpi. Here little Millerosteus nests between the origin of jaws and the genesis of larger and larger taxa, culiminating in giant Dunkleosteus.

Not surprisingly, here again,
phylogenetic miniaturization attends the genesis of new body parts. In this case placoderm mandibles appear in ultra tiny Bianchengichthys, a taxon smaller than both its predecessors and successors (Fig 1).

Here as well,
you can clearly see the origin of the entire clade of placoderms from jawless armored taxa with pointed snouts, like Poraspis (Fig 1). That matches the pointed snout and heavily armored morphology of the basalmost tested placoderm, Qilinyu (Fig 1).

Figure 2. Origin of jaws from the ostracoderm, Hemicyclaspis, Thelodus, Acipenser (sturgeon) and Chondrosteus.

The dual origin of jaws
here in placoderms (Fig 1) and separately in gnathostomes (Fig 2) was recovered by the LRT, contra traditional hypotheses seeking a single origin of jaws in vertebrates.

These appear to be novel hypotheses of interrelationships
and developmental biology. If not please provide a citation so I can promote it here.

PS
Has anyone else noticed that prior to 2010 most papers seem to have been written by one author? Rarely a pair of authors? This contrasts with more recent papers in which that number grows, often to eight or ten. Are scientists more magnanimous in the last decade (= more willing to share credit)? Give a boost to assistants, students and post-grads within a university? Farming the work out to others at other universities (thereby seeking more affinity with anonymous referees or skill sets not found locally)? Or taking on assignments and working with technologies that are much too involved for a single aging author who still holds sway but doesn’t want to learn new software? Just curious…

References
Stensiö EA 1959. On the pectoral fin and shoulder girdle of the arthrodires. K. svenska VetenskAkad. Handl. (9):2.

wiki/Coccosteus
wiki/Mcnamaraspis
wiki/Dunkleosteus
wiki/ANU244 not yet posted
wiki/Eastmanosteus
wiki/Arthrodira
wiki/Placodermi
wiki/Heterosteus
wiki/Incisoscutum
wiki/Homosteus
wiki/Dickosteus
wiki/Millerosteus

Tenontosaurus enters the LRT transitional to duckbill dinosaurs

Often portrayed as the victim
of a frenzied flock of Deinonychus (Fig 1), the pre-ornithopod, Tenontosaurus (Ostrom 1970, Figs 1, 2), enters the large reptile tree (LRT, 2150 taxa) transitional between Late Jurassic Dryosaurus (Fig 2) and Late Cretaceous duckbills like Edmontosaurus (Fig 2).

Figure 1. Cover art for the book Raptors! by Don Lessem, featuring Deinonychus without feathers, as requested by the author, attacking Tenontosaurus.

The Changchunsaurus > Edmontosaurus clade
nests between the stegosaurs (Lesothosaurus) and ceratopsians (Laquintasaura) (in the LRT. Basalmost ornithopod, Changchunsaurus, is from the Early Cretaceous.

According to Wikipedia,
“Throughout the Cloverly Formation, Tenontosaurus is by far the most common vertebrate, five times more abundant than the next most common, the ankylosaur Sauropelta.”

Figure 2. The origin of ornithopods as told by skulls beginning with Daemonosaurus in the Late Triassic and ending with Edmontosaurus in the Late Cretaceous. The last three, Dryosaurus, Tenontosaurus and Edmontosaurus are shown to one scale. Others above are shown to another scale.

Tenontosaurus is one of the earliest taxa
with a hyperelongated tail provided with the same tall neural spines and deep chevrons that characterize ornithopods. These, along with a longer length create what seems to be an oversize tail, which readily identifies Tenontosaurus. The hands retained dull claws on five short fingers. These would evolve to become flat hooves in Edmontosaurus. Manus digit 1 is retained in Tenontosaurus, then lost in Edmontosaurus. Pedal digit 1 is retained in Tenontosaurus, then lost in Edmontosaurus.

References
Ostrom JH 1970. Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana. Peabody Museum Bulletin 35:1–234.

wiki/Changchunsaurus
wiki/Dryosaurus
wiki/Tenontosaurus
wiki/Edmontosaurus

Teyumbaita enters the LRT next to the rhynchosaur Hyperodapedon with a traditional, rather sticky controversy

This placement was a fait accompli.
Rhynchosaurs are truly bizarre. Derived rhynchosaurs, like Teyumbaita and Hyperodapedon (Fig 1) push the definition of ‘bizarre’ to its limits. And they are two of a kind.

The problem is, the addition of this taxon brings up, once again, the widespread and traditional rhynchosaur origin mistakes still taught at the university level in Benton’s Vertebrate Paleontology textbook.

Figure 1. Teyumbaita on the left compared to scale with Hyperodapedon, two highly derived rhynchosaurs. Note the palatine (lavendar) fused to the maxilla (green) creating a groove the dentary slide through. Note the baroque decoration of the Teyumbaita jugal. Distance from premaxilla curve to lateral temporal fenestra is 10 cm.

For the last eleven years, according to
the large reptile tree (LRT, 2152 taxa, rhynchosaurs, azhendohsaurs and trilophosaurs were ALL descendants of sphenodonts (= rhynchocephalians). If it was going to change, it would have changed a long time ago. It has not changed in eleven years.

Decades ago, two experts cherry-picking traits created the current problem.
Carroll (1988) revisiting Carroll (1977) reported, “It was long thought that rhynchosaurs were closely related to modern sphendontids on the basis of general similarities of the skull and dentition. The common presence of primitive features such as the lower temporal bar only points to their common origin among early diapsids. Although the dentition appears to be vaguely similar, it is fundamentally different.”

So what? All other traits are the same. Carroll was cherry-picking traits, otherwise known as “Pulling a Larry Martin.” Don’t do that. You’ll end up embarrassed.

“Sphenodontids have only a single row of acrodont teeth in the maxilla, but rhynchosaurs have multiple rows of teeth set in sockets. Sphenodontids have a second row of teeth in the palatine, but this bone is edentulous in the rhynchosaurs. What appear to be long premaxillary teeth in the rhynchosaurs are actually processes from the premaxillary bones. Sphenodontids have true premaxillary teeth.”

So what? That is evolution in progress. Carroll also made an easy mistake. The palatine in rhynchosaurs is not edentulous (Fig 2). It is toothy and anteriorly fused to the maxilla. That may be the cause of Carroll’s error in the years prior to software-assisted phylogenetic analysis.

Figure 2. Sphenodon, Priosphenodon and Teyumbaita palates. Double arrows show groove between maxilla teeth and palatine teeth a trait not found in other clades.

The other expert making mistakes was textbook author Michael Benton.
Benton (1983) reported, “Rhynchosaurs have no special relationship with the sphenodontids. The supposed shared characters are either primitive (e.g. complete lower temporal bar, quadratojugal, akinetic skull, inner ear structure, 25 presacral vertebrae, vertebral shape, certain character of limbs and girdles) or incorrect (e.g. rhynchosaurs do not have acrodont teeth, the ‘beak-like’ premaxilla of both groups is quite different in appearance, the ‘tooth plate’ is wholly on the maxilla in rhynchosaurs but on maxilla and palatine in sphenodontids).”

Benton did not realize the lower temporal bar was derived in sphenodontians. Early lepidosaurs don’t have it. Acrodont teeth are also derived from socketed teeth, so all sphenodontids had to do was stop fusing their teeth to their skull in order to go back to the socketed teeth found in rhynchosaurs. Rhynchosaurs stop fusing their ankles and stop fusing their teeth to their jaws. That’s a reversal or two. Benton was also cherry-picking triats, aka “Pulling a Larry Martin.”

This was two years before Benton’s first venture into software assisted phylogenetic analysis.

Figure 3. Cladogram from Benton 1985 in which he nests pterosaurs closer to lepidosaurs than to dinosaurs and other archosaurs.

Four years after receiving his PhD, at the innocent age of 29
Benton 1985 nested pterosaurs closer to lepidosaurs than to dinosaurs (Fig 3). That was never repeated again until Peters 2007. Benton 1985 also missed the more obvious connection of pterosaurs to Macrocnemus, Tanytrachelos and Tanystropheus recovered by Peters 2000, 2007. Again, too few traits and too few taxa were tested in Benton 1985.

Getting back to rhynchosaurs,
note the proximity of Trilophosaurus to rhynchosaurs and lepidosaurs in Benton’s first ever cladogram (Fig 3). The basic problem with Benton 1985 was the use of only 14 taxa. In 2011 the LRT resolved Benton’s issues with 200+ taxa, none of them suprageneric. Today, in 2022 the LRT affirms the proximity of trilophosaurs, rhynchosaurs and sphenodonts with 2152 taxa.

Figure 4. Subset of the large reptile tree, the Rhynchocephalia, from 2016. This clade also included Rhynchosauria, Azendohsaurus and Trilophosaurus. AND it still does.

Here’s a solution:
Build your own LRT with a wide gamut of taxa to find out for yourself whether or not rhynchosaurs and trilophosaurs nest with more primitive sphenodonts. If somehow they don’t, you better have a damn good selection of taxa more similar than sphendonts. So far, and I’ve looked at everything out there, I don’t think you’re going to find competing candidates, let alone another set of sisters.

References
Benton M J 1983. The Triassic reptile Hyperodapedon from Elgin: functional morphology and relationships. Phil. Trans. R. Soc. Lond. B 302, 605–717.
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Carroll RL 1977. The origin of lizards. In Andrews, Miles and Walker [eds.] Problems of Vertebrate Evolution. Linnean Society Symposium Series 4: 359–396.
Carroll RL 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and Co. New York.
Ezcurra MD 2016. The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, 4:e1778
Mantefeltro FC, Langer MC and Schultz CL 2010. Cranial anatomy of a new genus of hyperodapedontine rhynchosaur (Diapsida, Archosauromorpha) from the Upper Triassic of southern Brazil. Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 101: 27–52.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Schultz CL, Langer MC and Montefeltro FC 2016. A new rhynchosaur from south Brazil (Santa Maria Formation) and rhynchosaur diversity patterns across the Middle-Late Triassic boundary. Paläontologische Zeitschrift. in press (3): 593–609.

wiki/Teyumbaita
wiki/Rhynchosaur
wiki/Michael Benton

https://pterosaurheresies.wordpress.com/2011/09/24/moving-rhynchosaurs-and-trilophosaurs-back-into-the-rhynchocephalia-sphenodontia/

https://pterosaurheresies.wordpress.com/2013/07/29/kaikaifilusaurus-and-the-origin-of-the-rhynchosaurs/

https://pterosaurheresies.wordpress.com/2014/02/18/the-origin-of-rhynchosaurs-revisited/

https://pterosaurheresies.wordpress.com/2014/03/20/arguments-against-the-rhynchosaurrhynchocephalian-rhylationship/

https://pterosaurheresies.wordpress.com/2014/11/23/leptosaurus-another-transitional-taxon-between-rhynchocephalia-and-rhynchosauria/

https://pterosaurheresies.wordpress.com/2016/01/13/early-evolution-of-rhynchosaurs/

Shearsbyaspis: a 3D partial petalichthyid placoderm

In their description of Shearsbyaspis Castiello and Brazeau 2018 wrote:
“Stem-group gnathostomes reveal the sequence of character acquisition in the origin of modern jawed vertebrates.

That’s a tautology (= saying of the same thing twice in different words). The problem is Castiello and Brazeau picked the wrong stem-group(s) not knowing the origin of jaws occurred twice in vertebrates (Figs 2, 3). Neither involved derived petalichthyids, like Shearsbyaspis.

“The petalichthyids are placoderm-grade stem-group gnathostomes known from both isolated skeletal material and rarer articulated specimens of one genus. They are of particular interest because of anatomical resemblances with osteostracans, the jawless sister group of jawed vertebrates.

The problem is Castiello and Brazeau did not realize the difference between ‘resemblance’ and homology. In the large reptile tree (LRT, 2150 taxa, subset Fig 2) petalichthyids are not related to osteostracans like Hemicyclaspis (Fig 3) with roots in the Early Cambrian taxon, Haikouichthys. Yes, our fish ancestors are that ancient.

Because of this, they [petalichthyids] have become central to debates on the relationships of placoderms and the primitive cranial architecture of gnathostomes.

This is incorrect due to taxon exclusion and reliance on out-dated university textbooks. Basal petalichthyids are central to relationships of placoderms because petalichthyids are basal to other placoderms (Fig 2), but Shearsbyaspis is a derived petalicthyid, going its own way, away from the lineage that developed placoderm jaws.

Moreover, petalichthyids have nothing whatsoever to do with the primitive cranial architecture of gnathostomes. Extant sturgeons (Fig 3) provide that data.

Figure 1, Shearsbyaspis (top) to scale with Lunaspis (below) close to life size @72 dpi.

Castiello and Brazeau 2018 wrote:
However, among petalichthyids, only the braincase of Macropetalichthys has been studied in detail, and the diversity of neurocranial morphology in this group remains poorly documented. Using X-ray computed microtomography, we investigated the endocranial morphology of Shearsbyaspis oepikiYoung, a three-dimensionally preserved petalichthyid from the Early Devonian of Taemas-Wee Jasper, Australia.

Glad to see that Shearsbyaspis (Fig 1) is 3D, because Lunaspis (Fig 1) is not.

“We generated virtual reconstructions of the external endocranial surfaces, orbital walls and cranial endocavity, including canals for major nerves and blood vessels. The neurocranium of Shearsbyaspis resembles that of Macropetalichthys, particularly in the morphology of the brain cavity, nerves and blood vessels. Many characters, including the morphology of the pituitary vein canal and the course of the trigeminal nerve, recall the morphology of osteostracans. Additionally, the presence of a parasphenoid in Shearsbyaspis previously not known with confidence outside of arthrodires and osteichthyans) raises some questions about current proposals of placoderm paraphyly. Our detailed description of this specimen adds to the known morphological diversity of petalichthyids, and invites critical reappraisal of the phylogenetic relationships of placoderms.”

Accepting that invitation, the LRT presents that “critical reappraisal of the phylogenetic relationship of placoderms” in figure 2.

Figure 2. Subset of the LRT focusing on basal vertebrates including a dual origin of jaws in placoderms and gnathostomes. Here petalichthyids are basal placoderms.

Figure 3. Origin of gnathostome jaws from the ostracoderm, Hemicyclaspis, Thelodus, Acipenser (sturgeon) and Chondrosteus, which was a late surviving pre-shark with jaws sans teeth.

It’s so important to start and finish every project
using a valid cladogram. Simply add taxa to bring your own cladogram up to date. Otherwise all your studies are going to be off the mark, with misunderstood conclusions due to taxon exclusion.

References
Castiello M and Brazeau MD 2018. Neurocranial anatomy of the petalichthyid placoderm Shearsbyaspis oepiki Young revealed by X-ray computed microtomography. Palaeontology https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12345

For the first time µCT scans expose Effigia in several views

From the Bestwick et al 2022 abstract:
“Here, we restore the skull morphology of Effigia, perform myological reconstructions, and apply finite element analysis to quantitavely investigate skull function. We infer that Effigia was a specialist herbivore that likely fed on softer plant material, a niche unique among the study taxa and potentially among contemporaneous Triassic herbivores.”

Figure 1. Effigia skull in several views after µCT scanning from Bestwick et al. 2022. Colors added here. O = orbit. That giant mandibular fenestra and declining parietal are clues that many large and varied muscles attach one area to another, pulling in several directions. Note the internal nares are set rather anteriorly, preventing breathing if chewing – unless chewing is restricted to the area anterior to the choanae, which appears to be the case here.

To their credit,
the ten co-authors compared their poposaur, Effigia (Fig 1), to two convergent dinosaurs, Ornithomimus and Struthio, The authors also compared Effigia to Alligator in order “to assess the degree of functional convergence with the above named taxa.”

I guess one of the ten co-authors must have insisted on this based on a convergent ankle joint in Alligator (see below). Otherwise it is difficult to compare alligator to ostrich morphologies, diet, niche, locomotion, etc. Nevertheless, ten PhD co-authors thought this was a good idea.

Figure 2. Effigia reconstructed in the early days of ReptileEvolution.com

To their discredit,
the ten co-authors still believe in the invalid clade Pseudosuchia, which they define as archosaurs more closely related to crocodylians than to birds. In the LRT (subset Fig 3) all archosaurs more closely related to crocodylians than to birds are members of the Crocodylomorpha. That’s it. Full stop. Outgroup taxa to crocs + dinos (Fig 3) are not archosaurs, by definition. Since poposaurs occupy this node, they are not archosaurs.

Figure 3. Subset of the LRT focusing on the Poposauria, Crocodylomorpha and surrounding clades. Rescoring Effigia based on the µCT scans (Fig 1) did not affect its earlier placement in the LRT.

Poposaurs
in the large reptile tree (LRT, 2149 taxa, subset Fig 3) are shown below (Fig 4). Turfanosuchus nests as the most basal poposaur. Effigia nests as the most derived poposaur.

Figure 4. Poposauridae revised for 2014. Here they are derived from Turfanosuchus near the base of the Archosauria, where crocs split from dinos. Most closely related taxa are toothless.

Among the LRT poposaurs
(Fig 3), Bestwick et al listed Shuvosaurus 1x, Lotosaurus 1x, Silesaurus 0x, Sacisaurus 0x, Poposaurus 1x and Turfanosuchus 0x. The authors reported, “Phylogenetic relationships within Poposauroidea are relatively well resolved.”

The ten authors are kidding themselves and short-changing their readers by excluding several poposaurs (listed above). In the LRT relationships are completely resolved by including taxa excluded by Bestwick et al. who borrowed an invalidated cladgoram from co-author Sterling Nesbitt 2011, who was working on his doctoral dissertation and publishing that as a paper eleven years ago.

It’s never a good idea to give big assignments like ‘examining all pertinent taxa’ to young doctoral students. Such young people have the least experience. Mistakes are inevitable. And then it gets worse. We’ve seen some mistakes promoted by professors intent on selling traditional, but outdated hypotheses published in their own university textbooks. Doctoral candidates are dependent on the judgement and bias of their mentor professor. So they have to do what they are told to do. It’s a feudal system designed to maintain that system and squelch unapproved discoveries.

Bestwick et al confessed,
“The order in in which poposaurid bauplans were assembled and/or modified is currently unclear (referencing co-author Nesbitt 2011),”

That study by Sterling Nesbitt was shown to suffer from inaccurate scoring to such an extent that when rescored here the topology matched the LRT.

Figure 5. The mandible of Effigia is much smaller than the rostrum and palate. This, and a loose quadrate/articular joint enables the mandible to be quite mobile beneath the rostrum. Both are incorrectly shown in palatal view, but the point is made based on their comparative perimeters.

Bestwick et al concluded,
“Effigia possesses an unusual mosaic of mechanical features that most likely restricted habitual feeding functions to the anterior portion of its jaws. A shearing motion between the anterior parts of the mandible and rostrum during orthal closure would generated the least stress under modeling conditions.”

“Shearing” is usually done with shears = scissors. Scissors require a tight rotating joint that permits cutting at the precise junction of two sharp surfaces brought into close contact. That’s not what we see here (Fig. 5). Instead the mandible is smaller than the rostrum making it extremely loose and mobile. Apparently this obvious key to the Effigia feeding apparatus was overlooked by all ten co-authors.

What is the tenth man rule?
“The Tenth Man strategy essentially says that if nine people agree on a particular course, the tenth person must, in the context of this strategy, take a contrary approach so that all alternatives can be considered. In business, this process can help break “groupthink” and ensure that a business considers all options.”

Effigia okeeffeae
(Nesbitt and Norell, 2006) Carnian, Late Triassic, ~210 mya, ~ 2 m in length, was originally considered an early theropod dinosaur by Colbert, who collected the specimen in the late 1940s but never removed it from its jacket. A reassessment by Nesbitt and Norell (2006) and Nesbitt (2007) nested Effigia among the poposaurid rauisuchians based largely on the ankle, which they reported articulated in a crocodile-normal configuration, with a morphology similar to Alligator.

Yes, poposaurids are rauisuchians. For the same reason: crocodylomorphs and dinosaurs (including birds) are rauisuchians. They are all descendants of rauisuchians in the LRT (Fig 3).

Relying on ankle joints is no longer a paleo fad. The LRT employs 236 multi-state characters and 2100 taxa to determine tree topology and interrelationships.

This is yet one more reason why you need to build your own LRT, so you. too, can use this powerful tool with authority. Then, when you test your own wide gamut of taxa, you’ll have the confidence that taxon exclusion will not be your problem.

References
Bestwick J et al (9 co-authors) 2022. Cranial funtional morphology of the pseudosuchian Effigia and implications for its ecological role in the Triassic. AnatomyPubs. Special Issue Article. online
Nesbitt SJ and Norell MA 2006. Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda). Proceedings of the Royal Society B 273:1045–1048. online
Nesbitt S 2007. The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa. Bulletin of the American Museum of Natural History, 302: 84 pp. online pdf

AMNH Effigia webpage
wiki/Effigia

Cynognathus and those strange extended lumbar processes

This icon of the Synapsida and Cynodontia
took a surprisingly long time to come to the top of the pile. And since it is THE icon for these two clades, it’s no surprise where Cynognathus nests in the large reptile tree (LRT, 2149 taxa).

Figure 1. Cynognathus skull in several views at right. Not sure about those at left, which were not tested.

Cynognathus crateronotus
(Seeley 1895, Wynd et al 2018, Middle Triassic, 1.2m snout-vent length) extended its range across South Pangaea. No complete skeletons are known, so a composite (= chimaera) is created (Fig 3) based on Thrinaxodon proportions. The secondary palate is complete.

Figure 2. Cynognathus vertebrae. Ribs are largely missing here. Those lateral extensions are transverse processes of the lumbar vertebrae.

Note the robust lumbar transverse processes on Cynognathus
(Fig 2), a trait shared with Thrinaxodon (Fig 3). These appear to occur at the transition from lateral undulation-dominated locomotion (like a sprawling reptile), to less-undulating, limb-dominated, more erect locomotion (as in basal mammals).

Here’s a thought.
This change in locomotion strategies could have occurred during a burrowing phase in which the narrow tunnel itself environmentally constrained locomotion from a wider sprawl to a narrower tucking in (adduction) of the limbs. Vertebrate burrows were present during the time of Cynognathus (Groenewald, Welman and MacEachern 2001) and Thrinaxodon fossils have been found within burrows.

Figure 3. Cynognathus reconstructed and restored from related taxa along with some of the first few reconstructions and sculptures from a century ago. The new reconstruction includes a longer vertebral spine and smaller pelvis that previously restored.

Burrowing cynodonts laid eggs.
At the origin of reptiles (= amniotes) the lumbar ribs became reduced, enabling gravid females to stretch their abdomens laterally while carrying the new larger amniotic eggs. In extant lepidosaurs gravid females distend the lower abdomen (Fig 4). So when Cynognathus started burrowing, perhaps these large, transverse lumbar processes somehow protected the lumber region of gravid females. Males had similar lumbar regions because they were also burrowing. Genders have not yet been identified in these basal cynodonts.

Predecessors did not have large lumbar extensions. Neither did successors. That’s all I’m basing this hypothesis on. It needs to be further developed.

Figure 4. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

One last little oddity about Cynognathus
is in the palate (Fig 1). The anterior jugals curl medially isolating the ectopterygoid (orange) from the maxilla without a suborbital fenestra. I have not seen that in other tetrapods.

References
Groenewald GH, Welman J and MacEachern JA 2001. Vertebrate burrow complexes from the Early Triassic Cynognathus Zone (Driekoppen Formation, Beaufort Group) of the Karoo Basin, South Africa- Palaios.
Jenkins FA Jr 1967. The postcranial skeleton of African cynodonts. Peabody Museum of Natural History Yale University Bulletin 36.
Seeley HG 1894. Researches on the structure, organisation, and classification of the fossil reptilia.-Part IX, Section 1. On the Therosuchia: Philosophical Transactions of the Royal Society of London, series B, v. 185, p. 987-1018.
Seeley HG 1895. Researches on the Structure, Organization, and Classification of the Fossil Reptilia. Part IX, Section 5. On the Skeleton in New Cynodontia from the Karroo Rocks. Philosophical Transactions of the Royal Society of London B 186: 59-148.

wiki/Cynognathus