The spiny dogfish (Squalus) enters the LRT

Slow, low and slinky,
the spiny dogfish shark (Squalus acanthias, Linneaus 1758; up to 1m in length; Figs. 1, 2) enters the large reptile tree (LRT, 1634+ taxa) basal to the angel shark (Squatina, Fig. 4) and the eagle ray (Aetobatus, Fig. 5) on one branch, and basal to the classic sharks, the mako (Isurus) and hammerhead (Sphyraena) on the other branch. On the ancestral side, Squalus is derived from two other small slinky sharks each with a terminal mouth, Cladoselache (Fig. 3) and Chlamydoselachus.

Figure 1. The spiny dogfish, Squalus acanthi as, in vivo.

Spiny dogfish are bottom-dwellers.
A tiny spine precedes each dorsal fin. They exude a mild venom, a precursor trait to descendant sting rays. The rostrum is elongate, making the jaw underslung. The lateral gill slits are set low, anterior to the pectoral fins. The anal fin is absent. Note the straightening of the heterocercal tail.

Figure 2. Skull of Squalus acanthi as with DGS colors added according to tetrapod skulls.

Squalus retains a gill bar
lateral to the jaws (red). The orbit is enormous and so is the naris, so this hunter relies on sight and smell.

Figure 3. Classic reconstruction of Cladoselache, a shark-like taxon basal to higher sharks and rays. Note the presence of dorsal fin spines and an absent anal fin.

Figure 4. Squatina in vivo, lateral view. The large pectoral and pelvic fins give Squatina a broad, ray-like appearance in dorsal view. Note the lack of an anal fin. Distinct from Squalus, Squatina has a terminal mouth and retracted nares.

Figure 5. The spotted eagle ray, Aetobatus in vivo. Venom spines appear here, as well.

PS: Quick Reminder
The LRT nests guitarfish, like Rhinobatos, and skates with Isurus, not with this clade. And nests Manta with Rhincodon, the whale shark, not with this clade, despite the massive convergence.

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References
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Squalus

First non-pterodactyloid pterosaurian trackways ever described? …No

Updated April 18. 2020
The four-fingered manus tracks (identified below out of context as a rhamphorhynchid pes track) belong to a tenrec, not a pterosaur. Details here. 

Mazin and Pouech 2020
report on basal pterosaur tracks from the “Pterosaur Beach of Crayssac” (Upper Jurassic), which they consider novel.

From the abstract:
“New discoveries on the ichnological site known as “the Pterosaur Beach of Crayssac” (lower Tithonian, Upper Jurassic; south-western France) answer the question of terrestrial capabilities of non-pterodactyloid pterosaurs. If the terrestrial type of locomotion of pterodactyloid pterosaurs has been solved from ichnological evidence for more than twenty years, no tracks and trackways referable to non-pterodactyloid pterosaurs have ever been described.”

Not true. Peters 2011 included several anurognathid tracks and matched them to trackmakers (Fig. 1). We looked at the so-called ‘Sauria aberrante‘ from Patagonia earlier here in 2011.

Figure 1. A pterosaur pes belonging to a large anurognathid, “Dimorphodon weintraubi,” alongside three digitigrade anurognathid tracks and a graphic representation of the phalanges within the Sauria aberrante track.in

Continuing from the abstract:
“Thus, the debate on terrestrial capabilities of these non-pterodactyloids was based on morpho-functional studies, with the main conclusion that those pterosaurs were arboreal dwellers and bad walkers.”

Not true. Peters 2000a, b, 2011, demonstrated a bipedal ability in pterosaurs superior to that of extant bipedal lizards, (e.g. Chlamydosaurus).

The ‘bad-walker myth’ results from mythology promoted by Unwin and Bakhurina1994 with regard to several misinterpretations of Sordes pilosus. including the invalid binding of the hind limbs with a uropatagium along with the invalid continuation of the brachiopatagium trailing edge to the ankle.

Figure 2. Dimorphodon pes with shadows. Pedal digit 5 can swing beneath the metatarsus. Note elevated proximal phalanges.

“Six trackways referable to three non-pterodactyloid new ichnotaxa, maybe closely related to Rhamphorhynchidae, are described in this work. Their study leads to the conclusion that grounded non-pterodatyloids, at least during the Late Jurassic, were quadrupedal with digitigrade manus and plantigrade to digitigrade pes.”

This confirms work by Peters 2000a, b, 2011.

“They were clearly good walkers, even if hindlimbs are supposed to be hampered by the uropatagium, what could have constrained the terrestrial agility of these animals.”

A single binding uropatagium is a myth invalidated several years ago. See above.

“Thus, from ichnological evidence and contrary to the current hypotheses, non-pterodactyloid pterosaurs seem to have been good walkers even though their trackways are very rare or unidentified to date.”

This also confirms work by Peters 2000a, b, 2011.

Figuue 3.  Cosesaurus matched to Rotodactylus from Peters 2000.

Continuing from the abstract:
“This rarity could be due to behaviour rather than to functional capacities, many non-pterodactyloids being considered both littoral fishers and arboreal or cliff dwellers. However, the concept of non-pterodactyloid “good climbers and bad walkers” has to be modified to “good climbers and rare walkers”, unless many non-pterodactyloid ichnites have yet to be discovered.”

Many non-pterodactyloid ichnites have been discovered (Fig. 1). Unfortunately, they have been ignored and omitted by authors, including Mazin and Pouech. It’s never a good time to remember Dr. S. Christopher Bennett’s infamous threat, “You will not be published. And if you are published, you will not be cited.”

Figure 4. Crayssac track different from all others. Inset: Pes of Rhamphorhynchus muensteri JME-SOS 4009, no. 62 in the Wellnhofer catalog. NOTE ADDED APRIL 18, 2020. The Martin-Silverstone paper (link above) identifies this as a manus track. It belongs to a tenrec, not a pterosaur. 

This used to be considered
crankery. Now they confirm the heretical hypotheses, but claim them as their own.

Figur 5. Unique among Rhamphorhynchus specimens, Rhamphorhynchus muensteri (Wellnhofer 1975) JME-SOS 4009, no. 62 in the Wellnhofer catalog has a long digit 4.

BTW
Earlier a published Craysaac a basal pterosaur track was matched to the pes of a particular Rhamphorhynchus (no. 62, JME-SOS-4009; Figs. 4, 5) in a 2011 blogpost on digitigrade pterosaur footprints. I heard of the Crayssac rhamph-tracks years ago and am glad to see their present publication. Still awaiting the paper. When it comes: more details.

NOTE ADDED APRIL 18, 2020. The Martin-Silverstone paper (link above) identifies this as a manus track. It belongs to a tenrec, not a pterosaur.

Figure 6. Cosesaurus and Rotodactylus, a perfect match. Elevate the proximal phalanges along with the metatarsus, bend back digit 5 and Cosesaurus (left) fits perfectly into Rotodactylus (right).

We also have tracks made by pre-pterosaur fenestrasaurs.
Rotodactylus, UCB 38023, Moenkopi Formation (Peabody,1948; Peters, 2000a; Figs. 3, 6)

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References
Casamiquela RM 1962. Sobre la pisada de un presunto sauria aberrante en el Liassico del Neuquen (Patagonia). Ameghiniana, 2(10): 183–186.
Mazin J-M and Pouech J 2020. The first non-pterodactyloid pterosaurian trackways and the terrestrial ability of non-pterodactyloid pterosaurs. Geobios 16 January 2020. PDF
Peabody FE 1948.Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
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. 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification
Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.

Sauria aberrante MLP 61-IX-4-1 (Casamiquela, 1962)
Track D, Sundance Formation (Harris and Lacovara, 2004)
Track C, Sundance Formation (Harris and Lacovara, 2004)

https://pterosaurheresies.wordpress.com/2012/03/02/the-case-against-bipedal-pterosaurs

https://pterosaurheresies.wordpress.com/2011/08/09/pterosaurs-bipedal-quadrupedal-or-both/

Wulong: a new troodontid, not a microraptor-dromaeosaur

Poust et al. 2020
bring us news of a small, subadult theropod with some interesting traits, Wulong bohaiensis (Early Cretaceous; D2933). They considered the specimen a microraptorine dromaeosaurid.

Figure 1. Wulong in situ, plus the original published diagram. The specimen is somewhat surrounded by a few coprolites = cop.

By contrast, 
the large reptile tree (LRT, 1637+ taxa) nests Wulong among similar, small, long-legged troodontids, between Buitreraptor and Caihong. While this topology differs from that of other workers, the same can be said of nearly every clade in the LRT. That’s why this blog has been self-labeled ‘heretical’.

Figure 2. Wulong skull, original diagram, DGS colors applied to bones and reconstruction based on the DGS tracings.

So, why the different views?
That appears to be due to taxon exclusion. There is no indication in the text that Buitreraptor and Caihong were included in analysis. There is no indication that the authors created a reconstruction, which helps identify bones, their ratios and proportion in crushed taxa like Wulong. More importantly…

Figure 4. Wukong manus DGS tracing and reconstruction. Note the 180º rotation of the manus relative to the radius and ulna.

… several taxa converge on birds
and small feathered theropods converge with each other in the LRT. The differences between the clades should not be determined by a few traits (= Pulling a Larry Martin), but here are gleaned after phylogenetic analysis of several hundred traits. As mentioned earlier, you can’t nest a specimen within a clade by a small number of cherry-picked traits because there is so much convergence within the Tetrapoda. Rather, run an analysis and find out which taxon is the last common ancestor of a derived clade. Those, then, are the validated clade members.

Figure 3. Wulong pelvis.

Figure 4. Wulong pedes, original tracing and reconstruction based on DGS tracings.

Uniquely
the coracoid is fenestrated in the middle. The ilium includes a prepubis process. Some feathers are preserved.

The authors report,
“Wulong is distinguished by several autapomorphic features and additionally, has many characteristics that distinguish it from its closest well-known relatives. Compared with Tianyuraptor and Zhenyuanlong, Wulong is small and its forelimbs are proportionally long.”

By contrast,
in the LRT Tianyuraptor and Zhenyuanlong are not related to troodontids, microraptorids or dromaoeosaurids. Tianyuraptor and Zhenyuanlong are basal to tyrannosaurids.

References
Poust AW, Gao C-L, Varricchio DJ, Wu J-L and Zhang F-J 2020. A new microraptorine theropod from the Jehol Biota and growth in early dromaeosaurids. The Anatomical Record. American Association for Anatomy. DOI: 10.1002/ar.24343

Lepidosaur bipedality and pelvis morphology: Grinham and Norman 2019

Grinham and Norman 2019

brings us a new look at 34 lepidosaur pelves with an emphasis on trends associated with bipedal locomotion. The authors illustrated 11 pelves (Fig. 1, white and yellow areas).

Figure 1. On the left, lepidosaur pelves from Grinham and Norman 2019, reordered phylogenetically here. On the right several tritosaur pelves and prepubes, most of which strongly demonstrate bipedal traits (elongate anterior ilium, increased sacral number). Yellow boxes indicate facultatively bipedal extant lepidosaurs.

From the Grinham and Norman abstract:
“Facultative bipedality is regarded as an enigmatic middle ground in the evolution of obligate bipedality and is associated with high mechanical demands in extant lepidosaurs. Traits linked with this phenomenon are largely associated with the caudal end of the animal: hindlimbs and tail. The articulation of the pelvis with both of these structures suggests a morphofunctional role in the use of a facultative locomotor mode. Using a three-dimensional geometric morphometric approach, we examine the pelvic osteology and associated functional implications for 34 species of extant lepidosaur. Anatomical trends associated with the use of a bipedal locomotor mode and substrate preferences are correlated and functionally interpreted based on musculoskeletal descriptions. Changes in pelvic osteology associated with a facultatively bipedal locomotor mode are similar to those observed in species preferring arboreal substrates, indicating shared functionality between these ecologies.”

Unfortunately, Grinham and Norman omitted
tritosaur lepidosaurs from their study. In the Triassic many of them became bipeds and among these, pterosaurs achieved bipedalism supported with four, five and more sacral vertebrae between horizontally elongate ilia, convergent with dinosaurs. The addition of the prepubis virtually extended the anchorage for the puboischial muscles. After achieving flight, beach-combing pterosaurs reverted to a quadrupedal configuration with finger 3 pointing posteriorly. Giant Korean bipedal pterosaur tracks are best matched to large dsungaripterid/tapejarid clade taxa.

Unfortunately, Grinham and Norman reported,

“A recently published molecular-based time-calibrated phylogeny for Squamata was pared down to match the species in our dataset.” Their genomic cladogram bears little to no resemblance to the large reptile tree (LRT, 1635+ taxa), which tests traits, not genes. Once again, genes produce false positives. 

The authors’ principal component analysis of the pelvis failed 

to isolate bipedal lepidosaurs from the rest. Grinham and Norman reported, “The shape of the pelvis in facultatively bipedal extant lepidosaurs falls within the overall morphospace of lepidosaurs generally.” This is also visible in their illustrated pelves (Fig. 1). They also reported, “However, it is generally found in a very concentrated area of that morphospace.” And “Conclusions can be drawn regarding pelvic morphology and substrate use, although not with the same clarity as for locomotor mode.”

Grinham and Norman 2019 conclude,
“we have used 3D landmark-based geometric morphometrics to demonstrate that the overall morphospace for the lepidosaur pelvis is broad and wide-ranging. Within this overall morphospace, a small region is occupied by facultative bipeds. The vast majority of this smaller morphospace overlaps that occupied by species that show a preference for arboreal habitats. Pelvic morphological adaptations relevant for living in an arboreal environment are similar to those necessary to facilitate facultative bipedality.”

That’s interesting with regard to
the arboreal abilities of volant basal bipedal pterosaurs and their ancestors. Maybe next time Grinham and Norman will expand their study to include tritosaur lepidosaurs.

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References
Grinham LR and Norman DB 2019. The pelvis as an anatomical indicator for facultative bipedality and substrate use in lepidosaurs. Biological Journal of the Linnean Society, blz190 (advance online publication) doi: https://doi.org/10.1093/biolinnean/blz190
https://academic.oup.com/biolinnean/advance-article-abstract/doi/10.1093/biolinnean/blz190/5687877Â
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Snyder RC 1954. The anatomy and function of the pelvic girdle and hind limb in lizard locomotion. American Journal of Anatomy 95:1-46.

Pterosaur prebubis

 

Another tiny paddlefish: Bandringa enters the LRT 2x

Resembling a tiny sawfish or paddlefish,
long-nosed Bandringa rayi (Zangrel 1969, 10cm; Fig. 1) is a Mazon Creek (Latest Carboniferous, 300mya) specimen preserving complete and articulated fossil with softparts in a small split nodule.

Traditionally considered a ctenocanthiform shark
(Elasmobranchii), the Bandringa holotype  (PF5686, Fig. 1) nests in the large reptile tree (LRT, 1635+ taxa, subset Fig. 5) with Polyodon, the extant paddlefish (Fig. 2), just outside the shark clade, transitional to the bony fish basal dichotomy.

Figure 1. Bandringa holotype, about 10cm long. This one nests with the paddlefish, Polyodon. The forward dorsal fin (fdf) is reidentified here as the right pectoral fin. Midlines and opercular lines are traced here.

The referred specimen,
(PF8442, Fig. 3) nests with Falcatus (Late Carboniferous; Fig. 4) in the LRT, separated from the holotype by one node (Fig. 5).

Figure 2. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.

Representing the traditional view, Sallen and Coates reported,
“Bandringa occupies an unresolved position within total-group Elasmobranchii, but displays similarities with sphenacanthids, hybodontiforms, and other member clades of the stem group. Bandringa is most simply interpreted as a freshwater, benthic, suction-feeding shark, and as a plausible analogue of modern sawfish (Pristidae). Juveniles of the Carboniferous Bandringa appear to have inhabited one of the earliest known shark nurseries at the brackish and marine Mazon Creek before migrating to freshwaters elsewhere.”

The problem with the traditional view
is the authors scored two specimens, the holotype and a referred specimen, as one taxon seen in two different views, creating a chimaera. This is an error according to the LRT, which nests the two specimens apart from one another, closer to other taxa.

The LRT resolves the phylogenetic problem raised by Sallen and Coates
as it nests hybodontiforms, like Hybodus, outside of the traditional Elasmobranchii, close to Polyodon and the rest of the bony fish. Such unforeseen (and previously untested) results is what makes the LRT such a powerful tool.

Figure 3. The referred specimen assigned to Bandringa nests with Falcatus (Fig. 4), only two nodes away from Polyodon. Scale bar = 1cm. This is a basal chimaera or ratfish. The pectoral fins were large, as in other chimaerids.

The fin on the convex side of the holotype
(Fig. 1) is actually the right pectoral fin, not the anterior dorsal fin. Though not scored, this makes the holotype of Bandringa more like Polyodon (Fig. 2), which also lacks an anterior dorsal fin.

Figure 4. Falcatus is a basal member of Elasmobranchii that nests with the referred specimen of Bandringa.

Teeth
The tiny holotype Bandringa (Fig. 1) is reported to have cladodont teeth (multi-cusped with one long central blade), but only simple cones with a broad base were illustrated by Zangrel 1969. Such teeth match those of Polyodon and are distinct from those of the large specimen attributed to Bandringa (Fig. 6).

Figure 5. Bandringa cladogram. The two juveniles are not that far apart phylogenetically, separated by only one node.

Wikipedia reports on Bandringa,
“Juveniles grew up to 10 cm (4 inches) to 15 cm (6 inches) long and adults grew up to 3 m (10 ft) long.” Putting aside how strange that sounds, this is understandable in light of the wide separation between juvenile and adult fossil sites. Salan and Coates reported, “No adult Bandringa specimens have been recovered from Mazon Creek, whereas only adults have been found in contemporary non-marine localities in Ohio and Pennsylvania.”

Figure 6. The large specimen assigned to Bandringa consists of a crushed skull matching the holotype, not the referred specimen. DGS helps visualize the shapes impressed into the substrate. The juvenile is about half the length of the ruler in the upper left corner.

Baird 1978 thought
Bandringa looked like the “spoonbill catfish” (= paddlefish, Polyodon). He further reports, “What appears to be an additional specimen of this shark, obtained by I. F. Mansfield in 1877, has come to light in the Princeton paleobotanical collection and has been catalogued among the fossil vertebrates as PU 19814. Despite poor preservation, its relative maturity (more than five times the linear size of the type individual) permits additions to our knowledge of the head morphology and teeth of Bandringa.” The large skull includes tiny and tricuspid teeth (Fig. 6), distinct from those seen in the tiny holotype (Fig. 1). If homologous, ontogeny comes with a change of morphology in tooth shape in these Late Carboniferous taxa. In extant taxa (Fig. 2), the adult teeth are also relatively smaller.

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References
Baird, D 1978. Studies on Carboniferous freshwater fishes. American Museum Novitates no. 2641:1-22.
Sallan LC and Coates MI 2014. The long-rostrumed elasmobranch Bandringa Zangerl,1969, and taphonomy within a Carboniferous shark nursery. Journal of Vertebrate Paleontology 34(1):22–33.
Wilkens LA 2009. The Paddlefish Rostrum as an Electrosensory Organ: A Novel Adaptation for Plankton Feedin. BioScience 57(May 2007):399-407.
DOI: 10.1641/B570505
Zangerl R 1969. Bandringa rayi, a new ctenacanthoid shark from the Pennsylvanian Essex fauna of Illinois. Fieldiana Geology 12:157–169.
Zangerl R 1979. New Chondrichthyes from the Mazon Creek fauna‭ (‬Pennsylvanian‭) ‬of Illinois.‭ ‬Mazon Creek Fossils‭ ‬449-500.

wiki/Bandringa
wiki/Elasmobranchii
wiki/Mazon_Creek_fossil_beds

A baby paddlefish enters the LRT looking like a baby shark

Earlier the primitive paddlefish
(Polyodon) entered the large reptile tree (LRT, 1634+ taxa) as the basalmost bony fish, distinct from and not related to traditional chondrostean relatives like the sturgeon (Psuedoschaphorhynchus), the bichir (Polypterus), and the extinct ‘chondrostean’ Chondrosteus.

Figure 4. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.

Today, a baby paddlefish,
lacking a long paddle bill (Fig. 2), enters the LRT. Why? Because the paddle bill of the adult stands out as an autapomorphic trait in the cladogram, and I’m looking for plesiomorphic transitional taxa that link clades together.  The short-snouted baby paddlefish (Fig. 2), looking just like a baby shark, but with an operculum, had the potential to do exactly that.

Figure 2. A shark-like juvenile paddlefish (Polyodon) has teeth and lacks a paddle-snout. Compare to the adult in figure 1. Legnth = 2.9cm. or slightly longer than one inch. Images from Grande and Bemis 1991, The pterygoid appears here for the first time.

Despite the lack of an elongate rostrum
and the score changes that brings, the baby and adult Polyodon nest together in the LRT.

Figure 3. Falcatus nests at the base of the shark clade, not far from baby Polyodon. Note the same underslung jaw loosely connected to the cranium + rostrum.

If ontogeny recapitulates phylogeny
in Polyodon, then the baby provides insight into the plesiomorphic morphology of a basalmost bony fish taxon, not far from a basalmost and transitional shark-clade taxa. That dichotomy likely extends back to the Late Silurian or Early Devonian. Thus, this long-sought and previously elusive mystery taxon might be best represented by a baby paddlefish. That means it was  under our nose all along!

BTW
in the ‘old’ days, Polyodon used to be called the ‘paddle-bill catfish.’ Not sure when the common name change took place.

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References
Grande L and Bemis WE 1991. Osteology and phylogenetic relationships of fossil and Recent paddlefishes (Polyodontidae) with comments on the interrelationships of Acipenseriformes. Society of Vertebrate Paleontology Memoir 1. Journal of Vertebrate Paleontology 11, Supplement to Number 1. 121pp.
Walbaum J 1792. Petri Artedi renovati. Part 3. Petri Artedi sueci genera Piscium in quibus systema totum ichthyologiae proponitur cum classibus, ordinibus, generum characteribus, specierum diffentiis, observationibus plumiris. Redactis Speciebus 2. Ichthyologiae, III: 723.

wiki/Polyodon

Tetraceratops revisited, yet again (Spindler 2020)

Updated June 14, 2021
with a new tracing of Martensius, a new sister for Tetraceratops.

Spindler 2020 brings new insight
to the problematic skull of Tetraceratops insignis (Figs. 1, 3-5; Matthew 1908). Traditionally considered a basalmost therapsid, it moves back just a notch when Spindler reports, “New information on ‘pelycosaurian’ character variation and relationships indicates that Tetraceratops represents a haptodontine-grade or (less likely) sphenacodontid ‘pelycosaur’.”

Figure 1. Tetraceratops fossil with tracing by Spindler and colors added using DGS methods. Here the quadrate (q) is a tabular + supratemporal. The pteryoid (pt( is a squamosal. The postorbital (po) is a postorbital + postfrontal + parietal. Some squamosal pieces are inside the orbit. Note the cervical rib (not colored) where the brain used to be. That’s the medial mandible exposed, not the lateral. 

By contrast
the large reptile tree (LRT, 1635+ taxa) now nests Tetraceratops between Saurorictus (Fig. 4) and the Limnoscelis (Fig. 4) clade (including Tseajaia and Orobates (Fig. 4)). The better data from Spindler 2020 moved Tetraceratops from a sister to Tseajaia, where the LRT nested it in 2011, prior to its new nesting. So this is a correction and a refinement.

Figure 2. Subset of the LRT focusing on Tetraceratops and its closest relatives.

A basic theme in most of these posts
is how to deal with convergence. In this case, the Milleretta (Fig. 4) clade produces all higher Lepidosauromorpha, including turtles, pareiasaurs, diadectids, Lepidosauriformes and Caseasauria, a clade traditionally associated with basal pelycosaurs… until tested with these other pertinent taxa.

Let the software decide where clades nest.
Don’t exclude candidates before testing them. That’s what the LRT does.

Even in 2020
Limnoscelis is not traditionally considered a reptile, let alone one related to Milleretta and Orobates, as indicated here in the LRT (subset Fig. 2).

Figure 3. Tetraceratops compared to several haptodine and basalmost therapsid taxa, the closest relatives according to Spindler 2020. Taxa at the transition from basal pelycosaurs to basal therapsids are well represented with subtle differences indicated.

Another theme is accurate reconstruction.
DGS (digital graphic segregation) permits specimen reconstruction without any freehand skills and attendant biases. Just copy and paste and let the reconstruction build itself in several views. Better interpretation comes with time and experience.

Figure 4. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta. Compare occiputs were preserved.

There is no argument about the well-preserved
and well-articulated anterior regions of the skull of Tetraceratops. The tusk like anterior premaxillary teeth find homologs in Limnoscelis.

The deeply curved mandibles
and narrow skull bauplan do not find homologs in currently tested taxa near Limnoscelis, but again, the larger anterior dentary teeth find homologs in Limnoscelis. These traits, as it turns out are convergent with those of basal pelycosaurs, which is a major cause for prior confusion.

The premaxilla of Tetraceratops is broader ventrally, taller, and more robust than in basal pelycosaurs. It more closely resembles the premaxilla of Limnoscelis.

The mandible is exposed in medial (not lateral) view. So a pelycosaur-like retroarticular process is not visible.

More questions attend the post orbital region of the skull.
In the present interpretation the squamosal was broken and displaced during taphonomy. Something pushed the neck into the back of the skull creating displacement and damage.  Related taxa have a similar tall straight post-jugal + post-postorbital rim, which was considered the rim, of a very large lateral temporal fenestra by other workers, including Spindler 2020. It is easy to see why workers thought that, especially when combined with the curved mandible. Putting that broken and rotated squamosal plus quadratojugal back in place (the curves match perfectly) is paramount to this new understanding.

The postorbital portion of the Tetraceratops skull
is shorter than in all other tested taxa, which makes it strange, but note the match with the mandible for reconstruction confirmation. Only Orobates (Fig. 4) s similar, but still longer.

The present reconstruction
(Fig. 5) indicates a narrow cranium in dorsal view, as Spindler notes, but a much broader palate is shown in the reconstruction, as in Limnoscelis, distinct from basalmost pelycosaurs, which have a narrow cranium and a relatively narrow palate.

The only other taxon with expanded prefrontals,
as seen in Tetraceratops, is Orobates, but to a lesser extent. Despite its plesiomorphic phylogenetic nesting, Tetraceratops has several derived traits not expected in the last common ancestor of Limnoscelis + Tetraceratops.

Figure 5. Tetraceratops tracing using DGS and freehand illustration by Spindler 2020. Note the occiput has been pushed anteriorly and up, like a garage door. A single cervical vertebra appears in the in situ opening between the occiput and parietals.

Testing
Following Spindler 2020 and others, I moved Tetraceratops to the base of the Pelycosauria in the LRT. That move adds a paltry 15 steps, demonstrating the great convergence in the two clades. Deleting all Lepidosauromorpha, other than Tetraceratops, nests it with Silvanerpeton. That’s where the Lepidosauromorpha would be, if not deleted, and far from the basal pelycosaurs trying to attract it.

Spindler 2015 reviewed the possibility of a sistership with Tseajaia,
but did so by cherry-picking a few traits (narrow skull, pterygoid transverse flange with strong dentition, bass-parasphenoid narrow and ventrally grooved, a real diastema, synapsid fenestra), thereby, “Pulling a Larry Martin.” The only way to really test taxa is to add them to a wide gamut phylogenetic analysis, like the LRT, that uses hundreds of traits and 1630+ taxa. Note, the new data moved Tetraceratops to a more primitive node relative to Tseajaia. So you have to test more taxa than just Tseajaia to resolve this issue. Better data sheds new light on many issues.

Spindler 2015 reports, “The main point of criticism is that the tests communicated by D. Peters did not use character lists and OTU lists capable of resolving a particular question. For example, plotting Tseajaia in the matrix of Liu et al. (2009) will count few similarities with Tetraceratops as synapomorphic, whereas the plesiomorphic features appear as autapomorphic in this pseudo‐clade for the lack of polarizing outgroup information. The suggested analysis ignores the requirement of matrix constraints that are designed for specific questions.” 

Liu et al. 2009 were considering the nesting of a new basal synapsid with double canines (Raranimus), completely unrelated to Tseajaia. In that cladogram Tetraceratops nested with Dimetrodon. Haptodus was the outgroup taxon and lateral temporal fenestra were presumed for Tetraceratops.

That brings to mind the possibility of an interesting test:
Where would Tseajaia, Tetraceratops, Limnoscelis and Saurorictus nest in a similar restricted test of Pelycosauria and basal Therapsida, with Haptodus as the outgroup taxon? The LRT and PAUP makes this easy by simply deleting taxa to the match the target taxon list. Results include the following:

1. Tseajaia alone nests without resolution with Haptodus, the two pelycosaur clades and the therapsid clade.
2. Tetraceratops alone nests without resolution with Ianthodon and the two pelycosaur clades.
3. Limnoscelis alone nests without resolution with Pantelosaurus and Cutleria + Hipposaurus.
4. Saurorictus alone nests without resolution with Ianthodon and the two pelycosaur clades.
5. All four added at once: They all nest with complete resolution as a sister clade to Pelycosauria.

Reverse testing
Going the other way, adding Pantelosaurus and Haptodus (Fig. 3) to a subset of the LRT focusing on Tetraceratops and its Lepidosauromorph kin nests those two taxa five nodes away from Tetraceratops, closer to the base of turtles + pareiasaurs.

Yes, any cladogram will nest every taxon,
with or without resolution. More characters do not produce greater resolution. More taxa, working like a larger diameter telescope,  produces greater resolution, while increasing confidence in the results by further minimizing taxon exclusion.

A review of the the figures above
demonstrates the distinct convergence between the two unrelated clades, a convergence that is best tested and resolved by phylogenetic analysis using a wide gamut of taxa. No polite dismissal of candidate taxa based should be considered, no matter how obvious such a dismissal appears warranted. Let the software sort out where every taxon nests. It worked for Casesauria. It worked for Tetraceratops, too.

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References
Amson E and Laurin M 2011.On the affinities of Tetraceratops insignis, an Early Permian synapsid. Acta Palaeontologica Polonica 56(2):301-312. online pdf
Conrad J and Sidor CA 2001.Re−evaluation of Tetraceratops insignis (Synapsida: Sphenacodontia). Journal of Vertebrate Paleontology 21: 42A.
Laurin M and Reisz RR. 1996. The osteology and relationships of Tetraceratops insignis, the oldest known therapsid. Journal of Vertebrate Paleontology 16:95-102. doi:10.1080/02724634.1996.10011287.
Liu J, Rubidge B and Li J 2009. New basal synapsid supports Laurasian origins for therapsids. – Acta Palaeontologica Polonica, 54 (3): 393‐400.
Matthew WD 1908. A four-horned Pelycosaurian from the Permian of Texas. Bulletin of the American Museum of Natural History XXIV, 183-185.
Spindler F 2014. Reviewing the question of the oldest therapsid. Paläontologie, Stratigraphie, Fazies (22) Freiberger Forschungshefte C 548: 1–7.
Spindler F 2015. The basal Sphenacodontia – systematic revision and evolutionary implications. PhD thesis, Technische Universität Bergakademie Freiberg. nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-171748
Spindler F 2020. The skull of Tetraceratops insignis (Synapsida, Sphenacodontia). Palaeovertebrata 43 (1)-e1. doi: 10.18563/pv.43.1.e1

https://www.palaeovertebrata.com/Articles/view/377

First pterosaur basihyal (Gladocephaloideus?, Gallodactylidae?)

Jiang, Li, Cheng and Wang 2020 bring us
the first evidence of a tiny medial hyoid bone, the basihyal (Fig.1; IVPP V 14189). Comparisons were made to “scavenger crows rather than chameleons.” Other pterosaurs have hyoids, but, until now, not a basihyal. Really, that’s all the authors needed to say. The rest of what they presented was filler, little of it accurate or valid.

Figure 1. Images from Jiang et al. 2020 scaled, rotated and layered. This is all that is known of this specimen. Micro -CL image shows hollow basihyal.

Overlooked by the authors,
Cosesaurus (Fig. 2), Sharovipteryx, Kyrgyzsaurus and Longisquama also have hyoids  The authors considered their specimen close to Gladocephaloideus (Fig. 3), which they considered a gallodactylid. Here Gladocephaloides nests with Gegepterus, a ctenochasmatid.

Figure 2. Cosesaurus hyoids in bright green.

Jiang et al. 2020 presented a greatly simplified cladogram
of pterosaur interrelationships… so simplified that it bears little resemblance to a more complete pterosaur cladogram. Kryptodrakon (junior synonym for Sericipterus) was misspelled Kryptondrakon.

Figure 3. Gladocephaloideus (the holotype) compared to the new specimen referred to Gladocephaloideus and its two sister taxa in the large pterosaur tree. Long necks in ctenochasmatids made several appearances by convergence.  Of particular interest, note the size of the pelvis in the JPM specimen, no larger than that of the much smaller MB.R. specimen. Lü et al considered the pelvis incomplete and it may be. Sister taxa are illustrated here from figure 2.

According to Jiang et al.
“The hyoids of primitive non-pterodactyloids only include the preserved ceratobranchials; this rod-like element is slender and quite long relative to the skull length. The ceratobranchial/skull length ratio is similar to most extant reptiles.” OK. Good to know.

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References
Jiang S-X, Li Z-H, Cheng X and Wang X-L 2020. The first pterosaur basihyal, shedding light on the evolution and function of pterosaur hyoid apparatuses. DOI 10.7717/peerj.8292

The ‘spine-brush complex’ of Akmonistion: dorsal fin? or dorsal shield?

A strange taxonomic addition today.
Akmonistion (Figs. 1, 2) nests in the large reptile tree (LRT, 1634+ taxa) between Falcatus (Fig. 3) and Heterodontus (horn shark. Fig. 4), a taxon that nests basal to members of the Holocephali.

So Akmonistion, Falcatus and Iniopteryx are basal members of Chondrichthyes (1880). These are late-surviving, but basal to both Elasmobranchii (1838, sans Rhincodon and Manta) and Holocephali (1832). Clearly a more plesiomorphic, but currently unknown Silurian or Devonian taxon without all the novel secondary sexual traits awaits discovery.

Figure 1. Akmonistion in situ, diagram and reconstruction from DGS methods. The tan crest portion appears to be the postparietals or at least the dorsal shield.

Traditional paleontology
considers the famous, bizarre ‘spine-brush’ of Akmonistion (Figs. 1,2) an enlarged and specialized dorsal fin. I will present evidence that it is something else.

Figure 2. Akmonistion, a relative of Stethacanthus, from Coates and Sequeira 2001.

What is a spine-brush complex?
Phylogenetic bracketing and simple morphology indicate the spine-brush is convergent with the thoracic shield in placoderms or the postparietals in catfish. This is either a completely novel structure or the elaboration of a smaller older structure from ancestral taxa. In any case the spine-brush complex is not a co-opted dorsal fin.

Ordinary dorsal fins
are made of parallel rods with roots that have sharp ventral tips buried deeply into fish flesh.

By contrast, the brush-shield complex
has a one-piece solid root, like a dorsal shield. If a shield, then primitively a low dorsal shield could have been operational at a low height with a few bumps, improving and growing.generationally by sexual selection.

According to Maisey 2009,
in Falcatus the spine appears relatively late in ontogeny and only in males. Unfortunately, we don’t have an ontogenetic series for Akmonistion. I can only imagine a greatly reduced or absent spine-brush when in the egg. Thereafter, if it followed the pattern in male Falcatus, the spine would appear at puberty.

Weighing one spine-brush hypothesis against another,
the “late-appearing, strange-looking anterior dorsal fin with spine” hypothesis competes with “the late-appearing, strange-looking, well-anchored thoracic shield” hypothesis.

The anterior dorsal fin placement patterns
of the few tested taxa in the LRT produce relatively few strong placement patterns. (Here LRT clades are divided by spaces).

• In Pseudoscaphorhychus, the sturgeon, a series of dorsal shields are present posterior to the skull, anterior to the pectoral fin.
• In Rhincodon, the whale shark, the dorsal fins are posterior to the pectoral fins
• In Falcatus (Fig. 2), the spine extends over the skull, rooted largely anterior to the pectoral fin, but directly over the pectoral girdle.
• In Iniopteryx, one small posterior dorsal fin appeared dorsal to the pelvic fin, but the pectoral fins are rooted dorsally.
• In Akmonistion (Fig. 2), the spine brush is rooted posterior to the skull, anterior to the pectoral fin. It could be the post parietal.
• The following taxa are not in the ancestry of Akmonistion and Falcatus.
• In Heterodontus, the horn shark, the dorsal fins are posterior to the pectoral fins.
• In Chimaera, the anterior dorsal fin is dorsal to the pectoral fin.
• In Belantsea, the anterior dorsal fin is dorsal to the pectoral fin.
• In Cladoselache, the dorsal fins are posterior to the pectoral fin.
• In Chlamydoselachus, the dorsal fins posterior to the pelvic fin.
• In Isurus, the mako shark, the dorsal fins are posterior to the pectoral fins.
• In Sphyrna, the mako shark, the dorsal fins are posterior to the pectoral fins.
• In all rays, mantas, skates and angel sharks, both dorsal fins are posterior to the pelvic fins
• In Polyodon, the paddlefish, the dorsal fin is posterior to the pelvic fins.
• In Hybodus, the the dorsal fins are posterior to the pectoral fins.

Figure 3. Falcatus skull. This taxon is close to Polyodon in the LRT. Note the anterior placement of the antler/spine/dorsal shield just behind the postparietals.

Does the LRT document any Akmonistion ancestors with dorsal shields?
In other words, is the dorsal shield of Akmonistion a reversal? a reappearance of something already in the gene pool? Or is it a novel trait?

FIgure 4. Ratfish (chimaera) and Heterodontus to scale.

We have three armored ancestors, according to the LRT.

• Jawless Birkenia has dorsal hooks and ossifications
• Jawless Hemicyclaspis (Fig. 5) is covered in armor.
• Semi-jawless sturgeons, like Pseudoscaphorhychus (Fig. 5), retain a series of dorsal plates and other armor.

Figure 5. The osteostracan Cephalaspis (above) compared to the sturgeon Pseudoscaphorhynchus (below). Note the dorsal armor just behind the skull.

Akmonistion zangerli (HMV8246; Coates and Sequeira 2001; Early Carboniferous) had a larger spine-brush complex. Note the great distance between the skull and pectoral girdle along with the short rostrum and large orbit.

Figure 6. Basal vertebrates and tetrapods 2020. Akmonistion nests between Falcatus + Iniopteryx and Heterodontus + the rest of the Chondrichtheys.

Stethacanthus altonensis (St. John and Worthen 1875; Late Devonian to Early Carboniferous; 70cm) has a posterior-leanding brush-spine.

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References
Bonaparte 1832. Iconografia della fauna italica, per le quatro classi degli animali vertebri. Rome, 78 pp.
Coates MI and Sequeira SEK 2001. A new stethacanthid chondrichthyan from the lower Carboniferous of Bearsden, Scotland. Journal of Vertebrate Paleontology. 21 (3): 438–459.
Maisey JG 2009. The spine-brush complex in Symmoriiform sharks (Chondrichthyes: Symmoriiformes), with comments on dorsal fin modularity. Journal of Vertebrate Paleontology, 29(1), 14-24.
St. John OH and Worthen AH 1875. Palaeontology of Illinois. Descriptions of fossil fishes. Geological Survey of Illinois, 6: 245–488.
Zangerl R 1984. On the microscopic anatomy and possible function of the spine-“brush” complex of Stethacanthus (Elasmobranchii: Symmoriida). Journal of Vertebrate Paleontology. 4 (3): 372–378.

wiki/Stethacanthus
wiki/Stethacanthidae
wiki/Akmonistion

A tadpole-like fish with a tetrapod-like backbone: Tarrasius problematicus

Updated March 1, 2020
with a DGS tracing of an in situ skull. 

Completely by convergence
this fish, Tarrasius problematicus (Traquair 1881; Viséan, Early Carboniferous 340mya; 10cm) developed morphologically distinct and diverse vertebrae (Fig. 1), like those of tetrapods, according to Sallan 2012.

Figure 1. From Sallan 2012, reconstruction of Tarrasius with colors added. Note the five vertebral regions. See Figure 1 updated below.

Figure 1 updated. Diagram of Tarrasius reconstructions from Sallan 2012, colorized here with the addition of the DGS tracing at lower right.

From the Sallan abstract:
“Here, I show that, Tarrasius problematicus, a marine ray-finned fish from the Mississippian (Early Carboniferous; 359–318 Ma) of Scotland, is the first non-tetrapod known to possess tetrapod-like axial regionalization. Tarrasius exhibits five vertebral regions, including a seven-vertebrae ‘cervical’ series and a reinforced ‘sacrum’ over the pelvic area. Most vertebrae possess processes for intervertebral contact similar to tetrapod zygapophyses. The fully aquatic Tarrasius evolved these morphologies alongside other traits convergent with early tetrapods, including a naked trunk, and a single median continuous fin. Regional modifications in Tarrasius probably facilitated pelagic swimming, rather than a terrestrial lifestyle or walking gait, presenting an alternative scenario for the evolution of such traits in tetrapods. Axial regionalization in Tarrasius could indicate tetrapod-like Hox expression patterns, possibly representing the primitive state for jawed vertebrates. Alternately, it could signal a weaker relationship, or even a complete disconnect, between Hox expression domains and vertebrate axial plans.”

Sallan reports,
“Tarrasius problematic us (Traquair 1881) is a fossil ray-finned fish (Actinopterygii) found in the Mississippian marine sediments of Scotland, phylogenetically branching off either the actinopterygian or actinopteran stem.”

By contrast
in the large reptile tree (LRT, 1655+ taxa) Tarrasius (Figs. 1, 2) nests with  Pholidophorus (Fig. 3), far from the origin of tetrapods, but deep within the lineage.

Figure 2 updated. From Sallan 2012 the NHM-P18062 skull of Tarrasius, the tadpole mimic. DGS colors added and used to create the reconstruction shown here. Note the complete lack of utility offered by the Sallan 2012 tracing.

Odd that a taxon like this has five distinct vertebral types.
It doesn’t even have a pelvis and hind fins,

Tarranius problematicus (Traquair 1881; Sallan 2012; Viséan, Early Carboniferous, 340mya; 10cm) was considered similar to the bichir, Polypterus, but phylogenetically close to Eusthenopteron and Phanerosteon. Here it nests at the base of the Pholidophorus clade.

Figure x updated. Subset of the LRT focusing on basal vertebrates (= fish).

References
Sallan LC 2012. Tetrapod-like axial regionalization in an early ray-finned fish. Proceedings of the Royal Society B 279:3264–3271.
Traquair RH 1881. Report on the fossil fishes selected by the Geological Survey of Scotland in Eskdale and Liddesdale. I. Ganoidei. Trans. R. Soc. Edin. 30,
14–71.

https://en.wikipedia.org/wiki/Tarrasiiformes

doi:10.1098/rspb.2012.0784