Archosauromorph Misinformation in the Encyclopedia of Geology, 2nd edition

In the 2nd edition of Encyclopedia of Geology,
Ezcurra, Jones, Gentil and Butler 2020 provide their guide to:

“How to Recognize Fossils of Archosauromorpha and Archosauriformes
The earliest archosauromorph lineages (e.g., Protorosaurus speneri, early tanystropheids) have a general body plan that resembles that of large modern lizards (e.g., varanids, teiids), but they are characterized by a series of unique evolutionary novelties in their skeleton that appeared in the common ancestor of the group during the Permian.

These diagnostic anatomical features include:

  1. snout representing around half or more of the skull length,
  2. posterior margin of skull roof defined by a low vertical lamina, 
  3. absence of a notochordal canal in the vertebral centra (with the exception of Aenigmastropheus, the earliest diverging archosauromorph), 
  4. neck with at least a slightly sigmoid profile,
  5. third cervical vertebra longer than the second one,
  6. anterior cervical vertebrae with rib facets on the centrum,
  7. last cervical and trunk vertebrae with bony buttresses (laminae) reinforcing rib articulations,
  8. absence of intercentra (ossifications that lie between the vertebral centra) posterior to the second cervical vertebra,
  9. very long cervical ribs extend parallel to the neck and possess an anterior process,
  10. long transverse processes in trunk vertebrae,
  11. humerus with low degree of torsion between the ends of the bone,
  12. and absence of an ossified distal carpal 5 (small wrist bone above the lateral-most digit).

“Most of the diagnostic features that characterize the archosauromorph body plan are concentrated in the vertebral column and are related to the elevation of the head above the level of the trunk and possible reduction of the mass of the vertebrae without a loss in strength. However, the functional significance of these changes and potential paleoecological implications remain mostly unexplored.”

Figure 2. From Ezcurra et al. 2020 with an overlay based on LRT results.

Figure 1.  From Ezcurra et al. 2020 with an overlay based on LRT results. The authors have not done their own testing, but are relying on popular consensus. That’s not good science.

Despite their sincere attempts, this is misinformation at its core. 

  1. Due to taxon exclusion Ezcurra et al. have no idea that the validated split between Lepidosauromorpha and Archosauromorpha occurred following Silvanerpeton in the Viséan (Early Carboniferous. The authors report: “middle-late Permian” for that split.
  2. No one can make a list of traits that all Archosauromorpha have in common and determine clade membership on that basis. In this respect the authors are attempting to  “Pull a Larry Martin“. You can only determine clade membership by a cladogram and look for that last common ancestor.
  3. Thus the only way to recognize an archosauromorph (definition: all taxa closer to archosaurs than to lepidosaurs) is to see where a taxon nests on a wide gamut cladogram like the large reptile tree (LRT, 1655+ taxa), where mammals and their synapsids ancestors are also members of the new Archosauromorpha. 

Ezcurra et al. consider the following members of the Lepidosauromorpha
to be basal members of the Archosauromorpha.

  1. Tanystropheidae. (Tanystropheus + Macrocnemus and kin) The LRT nests that clade in the Tritosauria and that clade in the Lepidosauria. Huehuecuetzpalli is in that lineage.
  2. Allokotosauria (Azendohsaurus + Trilophosaurus and kin) The LRT nests that clade in between Sphenodontia (= Rhynchocephalia) and Rhynchosauria within the Lepidosauria.
  3. Rhynchosauria (see above).

Ezcurra et al. consider the following clades
to be basal members of the Archosauromorpha.

  1. Prolacertidae (Prolacerta and kin, but not Protorosaurus) The LRT supports this assignment.
  2. Proterosuchidae (Proterosuchus and kin).The LRT supports this assignment.
  3. Erythrosuchidae (Erythrosuchus and kin). The LRT supports this assignment.
  4. Euparkeriidae (Euparkeria and kin). The LRT supports this assignment.
  5. Proterochampsidae (Proterohampsa and kin). The LRT supports this assignment.
  6. Doswelliidae (Doswellia and kin).The LRT supports this assignment except Vancleavea is a thalattosaur, an archosauromorph not related to Doswellia.

Ezcurra et al. consider the following clades
to be arguable basal members of the Archosauromorpha. Arguable? Test them! Based on their text and cladogram (Fig. 1) it is clear that Ezcurra’s team is following the authority of previous authors, not sure where some clades nest, rather than running the analysis themselves.

  1. Choristodera (Champsosaurus and kin) The LRT supports this assignment.
  2. Testudines (turtles, traditionally). The LRT nests this clade within the Lepidosauromorpha. Purported ancestors: Pappochelys is a sauropterygian archosauromorph in the LRT. Eunotosaurus is a lepidosauromorph not related to turtles, which arise from pareiasaurs in the LRT.
  3. Sharovipterygidae (Sharovipteryx and kin). The LRT nests this clade between tanystropheids and pterosaurs in the Tritosauria in the Lepidosauria. Ozimek is a long-limbed protorosaur, not related.
  4. Kuehneosauridae (Kuehneosaurus and kin. The LRT nests this clade among basalmost lepidosauriformes.
  5. Phytosauria (Phytosaurus and kin). The LRT supports this assignment.

It should be noted that Ezcurra et al. consider the clade
Pterosauria to be a part of the Avemetarsalia within the Archosauria. This myth was proven wrong twenty years ago. The LRT nests pterosaurs with tanystropheids and sharovipterygids within the Tritosauria and Lepidosauria. The authors have not done their own testing, but are relying on popular consensus. That’s not good science. Now, sadly, that misinformation is set in stone in the pages of the Encyclopedia of Geology.


References
Ezcurra MD, Jones AS, Gentil AR and Butler RJ 2020. Early Archosauromorphs: The crocodile and dinosaur precursors. Chapter in Encyclopedia of Geology, 2nd edition. Elsevier Inc. https://doi.org/10.1016/B978-0-12-409548-9.12439-X

Luchibang xingzhe enters the LPT… again… still not an istiodactlyid

Luchibang (Hone, Fitch, Ma and Xu 2020) is a new pterosaur from China
(Figs, 1–3) which we first learned about from a Flugsaurier 2018 abstract with photo (Hone and Xu 2018) and more recently from a pair of ‘Archosaur musings’ blogposts (links below).

Critically, Dr. Hone wrote in his blogpost:
“I didn’t include a phylogenetic analysis for a number of reasons, but notably as the specimen was so clearly an istiodactylid and their own relationships were rather unresolved, adding what was obviously a juvenile into the mix would have been a fair bit of work to not actually add any real information.” The paper includes a cladogram now, but it is heavily biased toward ornithocheirids and excludes important taxa discussed here in 2018.

Both then (233 taxa) and now (242 taxa)
with more highly resolved data the large pterosaur tree (LPT) nests Dr. Hone’s ‘young istiodactylid’ with the largest pterodactylids (Fig. 2), not istiodactylids or ornithochierids. We’ve known this for two years, so it is surprising to see this mistake perpetuated in a recent paper. Dr. Hone acknowledges the many ways in which Luchibang was ‘odd’ for an  istiodactylid: long legs, large feet, long metacarpals, short wings and a long neck.

Figure 1. The Erlianhaote specimen attributed by Hone and Xu 2018 to istiodactylidae nests in the LPT with the large derived pterodactylids.

Figure 1. The Erlianhaote specimen attributed by Hone and Xu 2018 to istiodactylidae nests in the LPT with the large derived pterodactylids.

It should be noted
that the skulls of the largest pterodactylids (Fig. 2) mimic those of istiodactylids to a remarkable degree. However, the rest of the body is distinctively different.

Figure 2. The Erlianhaote specimen nests with these pterodactylids in the LPT, not with Istiodactylus (Fig. 3). Compare to valid istiodactylids in figures 4–6/

Figure 2. The Erlianhaote specimen nests with these pterodactylids in the LPT, not with Istiodactylus (Fig. 3). Compare to valid istiodactylids in figures 4–6/

The new data from Hone et al. 2020
(Fig. 3) is more highly resolved, but the phylogenetic results are the same. Luchibang does not have the proportions of an istiodactylid, nor an ornithocheirid. Taxon exclusion might be to blame here. That, and an over reliant confidence on an earlier hunch by Dr. Hone (see quote above), a young professor known to toss out and ignore data on several previous occasions. Links can be found here, but most infamously here.

In the old days
papers would be submitted then reviewed by readers and colleagues. Nowadays, papers are reviewed prior to publication. Thereafter they may be cited, but are rarely reviewed. Dr. Hone notes that his team’s manuscript was rejected by another publication, not on the basis of its phylogenetic shortcomings, but on the suspicion that the odd proportions (for an istiodactylid) of the specimen resulted from a chimaera of unrelated pterosaur parts glued together to form a single complete specimen. That does not appear to be the case. All left and right parts are identical.

Figure 3. Istiodactylus has a shorter neck, longer wing finger and deep cristospine, among other traits not found in the new Erlianhaote specimen.

Figure 4. Istiodactylus has a shorter neck, longer wing finger and deep cristospine, among other traits not found in the new Erlianhaote specimen.

Oddly,
none of the referees mentioned in the blog posts by Dr. Hone (below) noted that Luchibang was a pterodactylid, not an istiodactylid. Unfortunately, that is the level of expertise we are dealing with out there in this topsy-turvy world, where the PhDs have no idea and thus leave it to the amateurs to do the “fair bit of work” as Dr. Hone put it (see quote above).

Also oddly,
Pterodactylus antiquus (Fig. 2) was included in the Hone et al. analysis, but did not attract Luchibang as it did in the LPT. I have not checked the scores published by Hone et al., but Hone’s own words (see above) demonstrate an initial and continuing bias toward making Luchibang an istiodactylid, despite the many traits he considered odd.

Figure 3. New tracings from Hone et al. 2020 of Luchibang (spelled Luichibang in the caption). Valid istiodactylids (see below) have much larger wings, much shorter metacarpals, much shorter necks and much smaller feet.

Figure 3. New tracings from Hone et al. 2020 of Luchibang (spelled Luichibang in the caption). Valid istiodactylids (see below) have much larger wings, much shorter metacarpals, much shorter necks and much smaller feet.

The danger from the Hone et al. paper lies in the
supposition of Hone’s team that this ‘young istiodactylid’ would grow allometrically to someday match the proportions of a full-grown istiodactylid. The Hone team does not yet realize that as tritosaur lepidosaurs, pterosaurs grow isometrically, with hatchlings having identical proportions to adults, as demonstrated by the JZMP embryo ornithocheirid.

The largest ornithocheirid

Figure 6. The unnamed largest ornithocheirid, SMNK PAL 1136

As you can see 
valid istiodactylids have much larger wings, much shorter metacarpals, much shorter necks and much smaller feet.

Figure 7. Luchibang skull in situ and reconstructed. Contra Hone et al. 2020, the cranial portion of the skull is visible and can be reconstructed.

Figure 7. Luchibang skull in situ and reconstructed. Contra Hone et al. 2020, the cranial portion of the skull is visible and can be reconstructed. The skull does resemble that of istiodactlyids by convergence, but details overlooked by the authors indicate otherwise.

Hone reported,
“apart from the back of the skull, the tail and few tiny bits, everything is there.” Using DGS methods, here (Fig. 7)  the scattered parts making up the face and back of the skull were identified, colored and reconstructed. Below (Fig. 8) the complete tiny tail is identified along with a reconstruction of the pelvis and a possible egg shell.

Figure 8. Pelvic area of Luchibang from Hone et al. 2020 with elements, including the overlooked tiny tail (green in ghosted oval) colorized. A possible egg is indicated here (blue).

Figure 8. Pelvic area of Luchibang from Hone et al. 2020 with elements, including the overlooked tiny tail (green in ghosted oval) colorized. A possible egg is indicated here (blue).

Fellow pterosaur workers…
the LPT is an open access cladogram that helps one avoid the sort of mistakes encountered by the Hone team. Coloring the bones (DGS) using layers in Photoshop is a better way to identify crushed bones. Reconstructions are essential.


References
Hone DWE and Xu 2018. An unusual and nearly complete young istiodactylid from the Yixian Formation, China. Flugsaurier 2018: the 6th International Symposium on Pterosaurs. Los Angeles, USA. Abstracts: 53–56.
Hone, DWE, Fitch AJ, Ma F, and Xu X 2020. An unusual new genus of istiodactylid pterosaur from China based on a near complete specimen. Palaeontologica Electronica 23(1):a09 Online link to PDF

https://archosaurmusings.wordpress.com/2020/03/09/a-long-overdue-welcome-to-luchibang/

https://archosaurmusings.wordpress.com/2020/03/10/ten-years-in-the-making-of-luchibang/#comment-105683

https://pterosaurheresies.wordpress.com/2018/08/11/flugsaurier-2018-young-istiodactylid-nests-with-tall-pterodactylids-in-the-lpt/

Revisiting the bonefish, Albula

Revised March 13, 2020
with new comparisons to Flagellipinna and Salmo.

Albula facial bones
(Fig. 1) have been reidentified and now this taxon nests with the long-nosed coral nipper and triggerfish mimic, Flagellipinna (Fig. 3), Like other primitive fish, Albula has 31+ presacral vertebrae. Derived fish have fewer and sometimes far fewer presacral vertebrae. In Albula the pelvic fins are located posteriorly. Derived fish have anterior pelvic fins, sometimes beneath and between the pectoral fins.

Figure 1. Albula vulpes skull with highly derived facial bones reidentified here. Note the lateral premaxillary processes and 'floating' cheek bones. Green vertebrae are caudals.

Figure 1. Albula vulpes skull with highly derived facial bones reidentified here. Note the lateral premaxillary processes and ‘floating’ cheek bones. Green vertebrae are caudals.

Albula vulpes (Linneaus 1758; 105cm in length) is the extant bonefish. It feeds on deep seafloor and tidal invertebrates. Note the floating cheekbone, dorsal nares, open rostrum, shark-like premaxilla, and large frontal. The large number of pre-sacral vertebrae is a primitive trait.

Figure 3. Flagellipinna is a sister to the bone fish, Alubula, in the LRT.

Figure 3. Flagellipinna is a sister to the bone fish, Alubula, in the LRT.

Figure x. Updated subset of the LRT, focusing on basal vertebrates = fish.

Figure x. Updated subset of the LRT, focusing on basal vertebrates = fish.

Careful readers will note
the teleost portion of the large reptile tree (LRT, 1656+ taxa) has been changing and improving almost daily based on corrections applied wherever low Bootstrap scores are recovered. That’s what you have to do.


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/Bonefish – Albula

Finding cheek bones in the banded rudderfish, Seriola zonata

Seriola zonata, the banded rudder fish, 
is an extant fish occupying the basal node in a clade that includes the giant oarfish, small sticklebacks and tiny seahorses in the large reptile tree (LRT, 1655+ taxa). Sticklebacks (Fig. 2) have a large jugal, but that bone is missing in the line art illustration by Gregory 1933 (Fig. 1) of the more primitive S. zonata. That’s a phylogenetic problem needing a solution. You can find those bones in the facial scales in the photo of S. sonata (Fig. 1). Problem solved?

Figure 1. Gregory 1933 did not illustrate a jugal and lacrimal for Seriola zonata, but the cladogram indicates they should be there. We find them in the photo.

Figure 1. Gregory 1933 did not illustrate a jugal and lacrimal for Seriola zonata, but the cladogram indicates they should be there. We find them in the photo.

Maybe.
At this point I am guessing that Gregory overlooked those bones in his drawing. Otherwise S. sonata must nest with more highly derived taxa that also lack a lacrimal and jugal. That causes other issues. This is one of those problems in which a feedback loop from the LRT back to the data was helpful to resolve this issue… if valid.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

It is worthwhile to compare the skull of
S. zonata, to that of the stickleback, Gasterosteus (Fig. 2). Other than size, the two score similarly. Note the anteriorly migrated jaw joint on Gasterosteus, the stickleback, further emphasized in even more derived pipefish and sea horses,

Figure 2. Skull of the stickleback, Gasterosteus, with bones colored here. Compared to figure 1.

Figure 2. Skull of the stickleback, Gasterosteus, with bones colored here. Compared to figure 1.

The use of transparent color overlays
(Fig. 1) and Digital Graphic Segregation (DGS) enabled this experiment to be shared in ways that line drawings cannot do as well.

Seriola zonata (Valenciennes 1833; commonly 50cm, up to 75cm) is the extant banded rudderfish. Large individuals (over 10 inches) have no abdominal bands,  but a raccoon-stripe on the eye and an iridescent gold stripe on the side are present. Adults are usually called amberjacks. Striped juveniles are usually called pilotfish.


References
Valenciennes A in Cuvier G and Valenciennes A 1833. Histoire naturelle des poissons. Tome neuvième. Suite du livre neuvième. Des Scombéroïdes. 9: i-xxix + 3 pp. + 1-512. Pls. 246-279.

wiki/Seriola
wiki/Amberjack

The four-eyed fish (Anableps) revisited

Updated December 17, 2020
with the addition of Fundulus to the LRT, Anableps moves away from Amia and Anguilla (Fig. 1). Here’s the updated portion of the cladogram:

Figure 1. Subset of the LRT focusing on the ray fin only clade of bony fish. Fundulus (yellow) is the new taxon. It attracted Anableps. Various convergent eel-like taxa are shown in baby blue.

Figure x. Subset of the LRT focusing on the ray fin only clade of bony fish. Fundulus (yellow) is the new taxon. It attracted Anableps. Various convergent eel-like taxa are shown in baby blue.

Figure 4. Amia, Anableps and Anguilla are related to one another in the LRT.

Figure 1. Amia, Anableps and Anguilla are now related to one another in the LRT.

This increasingly odd crocodile-mimic,
Anableps (Figs. 1-3), now nests between primitive bowfins and eels (Fig. 1) in the large reptile tree (LRT, 1655+ taxa; subset Fig. 3). The posterior placement of the pelvic fins is a clue to this fish’s primitive status. The ‘apparent’ lack of cheek bones was a problem that nested Anableps elsewhere earlier.

Figure 3. The four-eyed fish, Anableps, from three data sources. Compare to Fundulus in figure 4.

Figure 3. The four-eyed fish, Anableps, from three data sources. Compare to Fundulus in figure 4.

Previous data (Fig. 1) from Gregory 1933
was just supplemented by incomplete CT scans from Michel 2015 (Fig. 2). I needed this data to understand the vestigial and displaced cheekbones of Anableps that produced the current scores in the LRT. The readily apparent elevation of the orbit was accompanied by a similar, but until now overlooked elevation and shrinkage of the jugal (cyan) and postorbital (amber).

Figure 3. The four-eyed fish, Anableps, from three data sources. Compare to Fundulus in figure 4.

Figure 4. Skull of Fundulus from Gregory 1938. Compare to Anableps in figure 3.

Anableps tetrophthalmus
(originaly Cobitis anableps Linnaeus 1758, Scopolis 1777; 32 cm) is the extant four-eyed fish (aka: cuatro ojos), a surface predator of insects that fall into fresh waters or are preyed upon on shallow shors where they beach themselves to eat. Traditionally Anableps is a member of the (as yet untested) guppy family. Here it nests between the bowfin, Amia, and the American eel, Anguilla (below). Note the elevation of the jugal and postorbital, along with the elevated orbit. The naris is dorsal with an incurrent anterior tubular, pendant one near the mouth and the excurrent one near the orbit, as in eels. The fossil record is as yet unknown. Females are much larger than males. Internal fertilization (with a modified tubular anal fin) leads to live birth (viviparity) of up to 14 young.


References
Gregory WK 1933. Fish skulls. A study of the evolution of natural mechanisms. American Philosophical Society 23(2) 1–481.
Michel KB, Aerts P, Gibb AC and Van Wassenbergh S 2015. Functional morphology and kinematics of terrestrial feeding in the largescale foureyes (Anableps anableps). The Company of Biologists Ltd. Journal of Experimental Biology (2015) 218, 2951-2960 doi:10.1242/jeb.124644

 

Tiny Gregorius (Late Mississipian) revisited

As mentioned
yesterday, some changes have come to the basal vertebrates portion of the the LRT (Fig. 3). Here are the first of many highlights.

Gregorius rexi (Bear Gulch Fm. Serpukhovian, Latest Mississipian; Fig. 1) has not moved from its node in the large reptile tree (LRT, 1655+ taxa),
but the moray eel, Gymnothorax (Fig. 2), and the gulper eel, Eurypharynx, have moved to nest with goldfish-sized Gregorius.

Figure 1. Tiny Gregorius rexi nests basal to moray and gulper eels and also basal to all bony fish in the LRT.

Figure 1. Tiny Gregorius rexi nests basal to moray and gulper eels and also basal to all bony fish in the LRT. The yellow zone represents the pharyngeal bars that act as a second set of jaws in the related moray eel in figure 2. Shown life size.

Figure 2. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.

Figure 2. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.

Gregorius rexi (Lund and Grogan 2004; Bear Gulch Fm. Serpukhovian, Latest Mississipian) is traditionally considered a type of two-spined ratfish. In the LRT Gregorius is a late-surviving proximal outgroup to the Osteichthyes, the bony fish iincluding earlier placoderms, acanthodians and stem tetrapods. It retains the dorsal spines of its ancestor, Hybodus. It is not clear what sort of pectoral and pelvic fins Gregorius had due to matrix damage, but descendant taxa, like the moray eel, lack fins.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

Gymnothorax afer (Bloch 1795, type genus; 2m) Gymnothorax funebris (Ranzani 1839) is the extant green moray eel, which has no limbs or fins and traditionally nests within the Teleostei. Here this ‘eel’ is derived from Gregorius, outside the major dichotomy that splits the Teleostei. Pharygneal jaws (former gill bars) race anteriorly to double capture prey and drag it back to the digestive system.

This is a novel hypothesis of interrelationships.


References
Bloch ME 1795. Naturgeschichte der ausländischen Fische. Berlin. v. 9. i-ii + 1-192, Pls. 397-429.
Lund R and Grogan E 2004. Five new euchondrocephalan Chondrichthyes from the Bear Gulch Limestone (Serpukhovian, Namurian E2b) of Montana, USA. Recent Advances in the Origin and Early Radiation of Vertebrates 505-531.
Valliant LL 1882. Sur un poisson des grandes profondeurs de l’Atlantique, l’Eurypharynx pelecanoides. Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences, Série D, Sciences Naturelles 95: 1226-1228.

Gregorius_rexi.html
wiki/Eurypharynx
wiki/moray eel

Changes to the basal vertebrate subset of the LRT

Over the past several weeks
and especially the last several days, several dozen included taxa in the LRT have been reexamined and re-scored based on comparisons to other included taxa. Apparently the teleost (bony fish) section of the large reptile tree (LRT, 1655+ taxa; Fig. 1) has reached some sort of critical mass of taxa in which each taxon now has one to several ‘similar-enough’ taxa to enable side-by-side comparisons to identify inconsistent interpretations, overlooked bones and miscellaneous errata. Some of the data comes in the form of fifty-year-old drawings. Others from published x-rays. Still others from carefully prepared skulls. Yet others are studied from small, low resolution images. Overlooked vestigial and hidden structures have been identified. Sutures have been redrawn. Reconstructions have shed light on bone splinters and shards.

Corrections revealed earlier errors. 
As I’ve said on several occasions, I knew nothing about fish morphology before this study, gaining knowledge with every taxon. To students of science, this is the process, perhaps delivered more transparently than traditional works. Thankfully, none of this was printed. Instead, online presentations like this permit corrections and invite comments during the process… not just after publication.

Some highlights in the list of changes to the LRT (Fig. 1) include:

  1. Three eels now nest with Amia, the bowfin, a basal teleost, despite the loss of several cheek bones that typically mark derived taxa.
  2. Two more eels now nest with Gregorius, the proximal outgroup taxon to the basal dichotomy that splits the bony fish.
  3. The odd whitefish, Albula, now nests with the tarpon, Megalops.
  4. The frogfish, Antennarius, now nests with the mudskipper, Periophthalmus, rather than the goosefish, Lophius. 

Over the next few days
these novel hypotheses and others will be presented so you can share in the process of discovery.

The LRT is a powerful tool
that highlighted earlier errors in a feedback loop. Having a fully resolved cladogram is no guarantee that the resulting tree topology is correct at every node. High Bootstrap scores remain the goal. Reexamination is part of the process.

Strange-spined Xenacanthus enters the LRT

Illustrations of Xenacanthus
typically show a skull with very few sutures. Usually you just see the palatoquadrate sutured to the chondrocranium (e.g. Fig. 1).

Figure 1. Xenacanthus diagram with dorsal vertebrae colorized. Note the difference between the skull of this species and the one in figure 2.

Figure 1. Xenacanthus diagram with dorsal vertebrae colorized. Note the difference between the skull of this species and the one in figure 2.

By contrast
in a traced fossil (Fig. 2) sutures clearly define individual bones… and they tell us what bone makes the cranial spine: a central extension of the postparietal.

Figure 2. Xenacanthus skull with DGS colors added to show the unfused mandible bones.

Figure 2. Xenacanthus skull with DGS colors added to show the unfused mandible bones. Image from Long 1995.

According to Wikipedia,
Xenacanthus decheni (Beyrich 1848; originally Pleuracanthus Agassiz 1837; Devonian to Triassic, 1m up to 4m in length) is a genus of prehistoric sharks. At least 21 species are known. Traits include:

  1. Freshwater
  2. Two knife-like cusps on teeth
  3. Serrated spine arises from back of skull
  4. Two (= split) anal fins
  5. The short broad pectoral and pelvic fins are the same size

Such two-pronged teeth
are also found in a more primitive relative from the Early Devonian, Doliodus (Fig. 3), originally considered the ‘oldest articulated chondrichthyan’ and a transitional taxa between acanthodians and sharks.

Figure 1. Doliodus skull and pectoral region with lateral reconstruction at right. Note the narrow pectoral region relative to the wide spread occiput. Apparently this fish had a narrower body than head.

Figure 1. Doliodus skull and pectoral region with lateral reconstruction at right. Note the narrow pectoral region relative to the wide spread occiput. Apparently this fish had a narrower body than head.

The head spine
(Figs. 1, 2) is distinct from the dorsal fin spines found in Hybodus and acanthodians (= spiny sharks). Phylogenetically it is also homologous with the anterior spine-brush complex of Akmonistion.

Figure 2. Akmonistan, a relative of Stethacanthus.

Figure 2. Akmonistion, a relative of Stethacanthus, Doliodus and Xenacanthus.

Note,
clade members are quite diverse and among the first taxa in the lineage leading toward bony fish in the large reptile tree (LRT, 1655+ taxa; subset Fig. x below).

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

References
Agassiz L 1837. Recherches Sur Les Poissons Fossiles. Tome III (livr. 8-9). Imprimérie de Petitpierre, Neuchatel viii-72.
Beyrich E 1841. Über Xenacanthus decheni und Holacanthus gracilis, zwei Fische aus der Formation des Rothliegenden in Nord Deutschland. Bericht Verhandle. k. preuss. Akad. Wissens. zu Berlin 1848: 24–33.
Long JA 1995. The Rise of Fishes. Johns Hopkins University Press. Baltimore and London.

wiki/Xenacanthus

Revisiting the Early Carboniferous tadpole-mimic Tarrasius

Earlier I trusted the reconstructions
of Sallan 2012 when adding Tarrasius problematicus to the large reptile tree (LRT, 1655+ taxa). I intend to rectify that mistake here with DGS tracings of the in situ fossil skull (Fig. 1).

Figure 1. 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.

Figure 1. 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.

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 with at the base of the clade that includes Pholidophorus (Fig. 3).

Distinct from other fish, the vertebral column of this tadpole-mimic is divided into cervical, dorsal, lumbar, sacral and caudal regions, despite lacking pelvic fins. Those divisions are not apparent in some of Sallan’s figures (Fig. 2).

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

The closest living representatives of Tarrasius
in the LRT are the salamander fish, Lepidogalaxias salamandroides, and the lizardfish, Trachinocephalus myops. The Pholidophorus clade includes the long nose gar, Lepidosteus osseous. Despite two dozen scoring changes, Tarranius only shifted two nodes from where it nested before.

Figure 2. Diagram of Tarrasius reconstructions from Sallan 2012, colorized here with the addition of the DGS tracing at lower right.

Figure 2. Diagram of Tarrasius reconstructions from Sallan 2012, colorized here with the addition of the DGS tracing at lower right. No wonder this taxon has been difficult to nest taxonomically.

Funny thing…
way back when I added Pholidophorus to the LRT, I felt I had to add pelvic and anal fins with a yellow overlay  (Fig. 3), because they were not apparent. On second thought, perhaps those fins should not have been added, given the morphology of Tarrasius (Fig. 2).

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Compare the one on the left to figure 2. No tested fish in the LRT is closer to Robustichthys than Pholidophorus.

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Compare the one on the left to figure 2. No tested fish in the LRT is closer to Robustichthys than Pholidophorus.

DGS (Digital Graphic Segregation) continues to be
a valuable graphic tool for sorting through the chaos of crushed fossils (Fig. 1). It was first employed to pick out the details of the pterosaur, Jeholopterus in 2003 (see blog masthead above). I’m seeing colorized bones more and more often in online publications where color does not cost extra. That works so much better than line art despite the misgivings of naysayers.


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.