Trimerorhachis: a late survivor of the fin/finger transition?

Figure 1. Trimerorhachis was considered a dvinosaurian temnospondyl. Here both Trimerorhachis and Dvinosaurus nest low on the basal tetrapod tree, close to the fin/finger transition.

Figure 1. Flattened Trimerorhachis was considered a dvinosaurian temnospondyl. Here both Trimerorhachis and Dvinosaurus nest low on the basal tetrapod tree, close to the fin/finger transition, not within the Temnospondyli. Both are late survivors of a Devonian radiation.

Wikipedia reports:
Trimerorhachis (Early Permian, (Cope 1878, Case 1935, Schoch 2013; up to 1m in length) is an extinct genus of dvinosaurian temnospondyl within the family Trimerorhachidae. The trunk is long and the limbs are relatively short. Many bones are poorly ossified, indicating that Trimerorhachis was poorly suited for movement on land. The presence of a branchial apparatus indicates that Trimerorhachis had external gills in life. The body of Trimerorhachis is also completely covered by small and very thin osteoderms, which overlap and can be up to 20 layers thick. The scales were more similar to fish scales than they were to reptile scales, according to Colbert 1955. However, Olson 1979 disputed that interpretation. Specimens are often preserved as masses of bones that are mixed together and densely packed in slabs of rock”

Figure 2. Trimerorhachis forelimb and hind limb in situ and reconstructed.

Figure 2. Trimerorhachis forelimb and hind limb in situ and reconstructed. Pawley 1979 did not report metacarpals or a pubis. It is possible and perhaps likely that only 4 metacarpals were present along with two phalanges, but its worth exploring all possibilities. 

As a late (Early Permian) survivor of a Late Devonian radiation
Trimerorhachis evolved by convergence certain traits found in other more derived tetrapods, like a longer femur and open palate (narrow, bowed pterygoids). Testing all possibilities while minimizing assumptions is the most valuable benefit of a large gamut phylogenetic analysis conducted by unbiased software. Workers used to eyeball specimens in the pre-computer days.

Figure 2. Trimerorhachis pelvis. The pubis is not ossified.

Figure 3. Trimerorhachis pelvis. The pubis is not ossified here, according to Pawley 1979, but see Fig. 1.

Like other workers,
Pawley 1979 considered Trimerorhachis close to Dvinosaurus (Fig. 7) and both thought to be derived from the basal temnospondyl Balanerpeton and Dendrerpeton. The large reptile tree (LRT) nests both taxa at the base of the Lepodpondyli, not closely related to Trimerorhachis and distinct from Temnospondyli. Pawley supports the hypothesis that aquatic ‘temnospondyls,’ like Trimerorhachis, had terrestrial ancestors. By contrast, the LRT nests Trimerorhachis with weak-limbed taxa more primitive than any temnospondyl.

Additionally
the LRT nests Batrachosaurus and Gerrothorax in the Dvinosaurus / Trimerorhachis clade. This clade features horizontally opposed dorsal ribs and an equally flattened skull. Another flattened taxon, Ossinodus, is closely related. I have not seen limb material for any of these taxa. Acanthostega is the closest taxon that preserves limbs.

Figure 3. Trimerorhachis hind limb and pes from Pawley 1979.

Figure 4. Trimerorhachis hind limb and pes from Pawley 1979 and reconstructed here.

Pawley 1979 noted,
“The vast majority of the [Trimerorhachis] specimens consists of ornamental cranial and pectoral girdle bones, intercentra, and larger elements of the appendicular skeleton. Neural arches, pleurocentra, ribs and distal limb elements are rare.” No sacrals were found by Pawley. No dorsal ribs had uncinate processes (like those in Ichthyostega and Eryops). The chevrons were long and tapered distally (creating a fin?). The interclavicle was diamond-shaped with a longer anterior portion.

Figure 4. Trimerorhachis humerus changes during ontogeny

Figure 5. Trimerorhachis humerus changes during ontogeny

The humerus
(Fig. 5) was  L-shaped and the degree of torsion varied between specimens from 45º to 90º. The distal end always exhibited a low degree of ossification.

Figure 6. Trimerorhachis cladogram. Gray area is the Temnospondyli clade.

Figure 6. Trimerorhachis cladogram. Gray area is the Temnospondyli clade.

Pawley considered
Trimerorhachis a secondarily adapted aquatic temnospondyl. All workers have noted the wide open palate vacuities that characterize most, but not all members of the Temnospondyli. By contrast, the LRT nests Trimerorhachis with taxa that had not yet left the water completely and shared a flat morphology with Tiktaalik and Panderichthys.

This is the second time
elongate limbs and digits have appeared by convergence in basal tetrapods. Earlier Pholidogaster and kin provided the first exceptions to the rule. Note that all known specimens of Trimerorhachis are Early Permian, some tens of millions of years later than the Late Devonian radiation of that clade. The Ichthyostega line is the one that ultimately produced crown Tetrapoda via a sister to Eucritta.

FIgure 8. Dvinosaurus nests with Trimerorhachis and also has ceratobranchial (gill) bones.

FIgure 7. Dvinosaurus nests with Trimerorhachis and also has ceratobranchial (gill) bones. The loss of the intertemoral is shown here in light green merging to the postorbital in orange. 

If these nestings are not correct
and Trimerorhachis ultimately nests higher on the basal tetrapod tree, then we’re witnessing massive convergence of another sort, convergence that allies Trimerorhachis with tetrapods at the fin/finger transition. I’d like to see limbs for Gerrothorax or any other plagiosaur, if available.

Figure 9. Ossinodus is a close relative of Trimerorhachis in the LRT.

Figure 8. Ossinodus is a close relative of Trimerorhachis in the LRT. 

By the way, I find this fascinating…
week after week, far and away the most popular page(s) on this blog continue to be on the origin of bats.

References
Berman DS and Reisz RR 1980. A new species of Trimerorhachis (Amphibia, Temnospondyli) from the Lower Permian Abo Formation of New Mexico, with discussion of Permian faunal distributions in that state. Annals of the Carnegie Museum. 49: 455–485.
Case EC 1935. Description of a collection of associated skeletons of Trimerorhachis. University of Michigan Contributions from the Museum of Paleontology. 4 (13): 227–274.
Colbert EH 1955. Scales in the Permian amphibian Trimerorhachis. American Museum Novitates. 1740: 1–17.
Olson EC 1979. Aspects of the biology of Trimerorhachis (Amphibia: Temnospondyli). Journal of Paleontology. 53 (1): 1–17.
Pawley K 2007. The postcranial skeleton of Trimerorhachis insignis Cope, 1878 (Temnospondyli: Trimerorhachidae): a plesiomorphic temnospondyl from the Lower Permian of North America. Journal of Paleontology. 81 (5):
Williston SW 1915. Trimerorhachis, a Permian temnospondyl amphibian. The Journal of Geology. 23 (3): 246–255.
Williston SW 1916. The skeleton of Trimerorhachis. The Journal of Geology. 24 (3): 291–297.

wiki/Trimerorhachis

Distribution of ‘key’ traits in basal tetrapods

Before the advent of phylogenetic analysis,
paleontologists attempted to define clades with a short list of synapomorphies. In this way they were getting close to the dangers of pulling a Larry Martin. Many taxa, like pterosaurs and Vancleavea were (and are) considered enigmas because they seemed to appear suddenly in the fossil record with a short suite of traits that did not appear in other reptiles. That was only true back then because paleontologists were only considering short lists of traits.

After the advent of phylogenetic analysis
considering long lists of traits, the rule of maximum parsimony allowed clades to include members that do not have a short list of key traits. For instance some reptiles, like snakes, do not have limbs, but that’s okay based on the rule of maximum parsimony as demonstrated in the large reptile tree (LRT, 977 taxa, subsets shown in Figs. 1-5).

Before the advent of phylogenetic analysis
Carroll (1988) divided basal tetrapods into labyrinthodonts and lepospondyls and presented short lists of key traits.

Labyrinthodonts

  1. evolved directly from rhipidistian fish
  2. labyrinthine infolding of the dentine
  3. palate fangs and replacement pits
  4. vertebral centra composed of more than one element
  5. otic notch
  6. large in size

Lepospondyls

  1. a heterogeneous assemblage of groups with perhaps several origins from among various labyrinthodonts
  2. simple (non-labyrinthine) teeth
  3. no palate fangs
  4. vertebral centra composed of one element
  5. no otic notch
  6. small in size

By contrast,
the large reptile tree introduces a non-traditional topology in which lepospondyls have a single origin. Below (Figs. 1-5) the distribution of several traits are presented graphically.

Figure 1. Distribution of the solid and open palate architectures in basal tetrapods in the LRT topology.

Figure 1. Distribution of the solid and open palate architectures in basal tetrapods in the LRT topology.

Open palate distribution
Basal tetrapods have a solid palate (Fig. 1) in which the pterygoid is broad and leaves no space around the medial cultriform process. Other taxa have narrow pterygoids and large open spaces surrounding the cultriform process. Still others are midway between the two extremes. Traditional topologies attempt to put all open palate taxa into a single clade. Here the open palate evolved three times by convergence.

Figure 2. Size distribution among basal tetrapods in the LRT topology

Figure 2. Size distribution among basal tetrapods in the LRT topology

The length of basal tetrapods
falls below 60 cm in Eucritta and more derived taxa. It also falls below 60 cm in Ostelepis, at the origin of Tetrapoda and Paratetrapoda. Phlegethontia has a small skull, but is otherwise like an eel, and so does not fall below the 60 cm threshold.

Figure 3. Distribution of single vertebrae among basal tetrapods in the LRT.

Figure 3. Distribution of single vertebrae among basal tetrapods in the LRT.

Single piece centra
appear in frogs + salamanders, microsaurs and Phlegethontia, by convergence. Intercentra appear in all other taxa.

Figure 6. Distribution of palatal fangs among basal tetrapods in the LRT.

Figure 6. Distribution of palatal fangs among basal tetrapods in the LRT.

Palate fangs
appear in all basal paratetrapods and tetrapods except Phlegethontia, Spathicephalus and Gerrothorax. Exceptionally, Seymouria also had palate fangs.

Figure 7. Distribution of the otic notch among basal tetrapods in the LRT.

Figure 7. Distribution of the otic notch among basal tetrapods in the LRT.

The otic notch
is widespread among basal tetrapods. Those without an otic notch include

  1. One specimen of Phlegethontia that loses posterior skull bones
  2. Six flat-skulled temnospondyls in which the tabular contacts the squamosal. Some of these, like Greererpeton, have figure data that lack an otic notch, but photos that have one.
  3. Salamanders and frogs that greatly reduce posterior skull bones.
  4. All microsaurs more derived than Microbrachis

Let me know
if I overlooked or misrepresented any pertinent data. This weekend I should be able to look at and respond to the many dozen comments that have accumulated over the last few weeks.

 

Basal Tetrapods, slightly revised

Figure 1. Click to enlarge. With the addition of Panderichthys and Anthracosaurus the position of Koilops and Deltaherpeton have shifted to the base of the Temnospondyli.

Figure 1. Click to enlarge. With the addition of Panderichthys and Anthracosaurus the position of Koilops and Deltaherpeton have shifted to the base of the Temnospondyli. Some of that shifting is due to rescoring.

After earlier identifying
phylogenetic miniaturization at the bases of several major clades in the large reptile tree (LRT, 969 taxa), I wondered if similar size-related patterns appear in basal tetrapods.

  1. Osteolepis is smaller than Eusthenopteron. Has anyone removed the scales from the fore fins of Osteolepis to see what the bones inside look like?
  2. Pholidogaster is much larger than Osteolepis, but Colosteus and Phlegethontia are successively smaller with smaller limbs.
  3. Ventastaga and Pederpes are successively smaller than Ichthyostega.
  4. Koilops is much smaller than Ventastaga and Pederpes
  5. Eucritta is much smaller than Proterogyrinus, both in overall size and in relative torso length. Eucritta nests at the base of the Seymouriamorpha + Crown Tetrapoda.
Figure 2. Basal tetrapod skulls in dorsal view.

Figure 2. Basal tetrapod skulls in dorsal view. Tetrapoda arise with flattened skulls. Paratetrapoda retain skulls with a circular cross section. 

 

A word about competing phylogenetic hypotheses…

…from Coates et al. 2002:
re: basal tetrapods: “Debates about phylogenetic hypotheses concerning these basal nodes are often intense, and conflicts arise over differing taxon and character sets, scores, and coding methods (see Coates et al. 2000; Laurin et al.2000).

And that comes eight yeas before
the advent of ReptileEvolution.com and this blog. So, readers, don’t trust one or another analysis (even this one) before giving them a test on your own or waiting for all the fallout to… fall out. At present, they are competing analyses.

At present
there are broad swathes of agreement in many published trees. The disagreements will ultimately iron themselves out. That some workers object to seeing new solutions to problems they feel they have solved already is just part of the process.

References
Coates MI, Ruta M and Milner AR 2000. Early tetrapod evolution. Trends Ecol. Evol. 15: 327–328.
Coates MI and Ruta M 2001 2002. Fins to limbs: What the fossils say. Evolution & Development 4(5): 390–401.
Laurin, M., Girondot, M., and de Ricqlès, A. 2000. Early tetrapod evolution. Trends Ecol. Evol. 15: 118–123.

A juvenile Anteosaurus? No.

Kruger et al. 2017
reported on a newly discovered ‘juvenile Anteosaurus skull BP/1/7074 (Figs. 1,2). This was also the subject of Kruger’s 2014 Masters thesis.

Unfortunately
in the therapsid skull tree, BP/1/7074 did not nest with Anteosaurus, but with Austraolosyodon (Figs. 1,2). Neither Kruger nor Kruger et al. presented a phylogenetic analysis.

So let’s talk about
this discrepancy and the importance of phylogenetic analysis. We’re long past the age of ‘eyeballing’ taxa.

Figure 1. The purported juvenile Anteosaurus skull, BP/1/7074 compared to he coeval Australosyodon.

Figure 1. The purported juvenile Anteosaurus skull, BP/1/7074 compared to he coeval Australosyodon. DGS colors have been applied to the bones of BP/1/7074.

From the 2017 abstract
“A newly discovered skull of Anteosaurus magnificus from the Abrahamskraal Formation is unique among specimens of this taxon in having most of the individual cranial bones disarticulated, permitting accurate delimitation of cranial sutures for the first time. The relatively large orbits and unfused nature of the cranial sutures suggest juvenile status for the specimen. Positive allometry for four of the measurements suggests rapid growth in the temporal region, and a significant difference in the development of the postorbital bar and suborbital bar between juveniles and adults. Pachyostosis was an important process in the cranial ontogeny of Anteosaurus, significantly modifying the skull roof of adults.”

Without a phylogenetic analysis,
it is not wise to assume you have a juvenile of any taxon, especially if you describe it as unlike the adult due to allometry when allometric growth has not been shown in related taxa. All of what Kruger et al. said about pachyostosis may be true, but it awaits a real juvenile Anteosaurus skull to present as evidence. Kruger et al. cited these:

Kammerer et al. 2011 reported that that Stenocybus acidentatus (IGCAGS V 361, Middle Permian, Cheng and Li 1997) is a juvenile Sinophoneus. Phylogenetic analysis nested that smaller skull lower on the therapsid tree.

Liu et al. 2013 thought they had found several short-faced juvenile Sinophoneus skulls. Phylogenetic analysis nested those smaller skulls lower on the the therapsid tree.

Figure 2. Kruger et al. 2017 figure 21. provided "Ontogenetic changes in the skull of Anteosaurus; A. juvenile; B, intermediate sized; C, adult sized, redrawn from Kammerer 2011. Their figure 20 labeled the intermediate sized skull as Titanophoneus. So this is a phylogenetic series, not an ontogenetic one.

Figure 2. Kruger et al. 2017 figure 21. provided “Ontogenetic changes in the skull of Anteosaurus; A. juvenile; B, intermediate sized; C, adult sized, redrawn from Kammerer 2011. Their figure 20 labeled the intermediate sized skull as Titanophoneus. So this is a phylogenetic series, not an ontogenetic one.

 

Misdirection
In Kruger et al. 2017 their figure 21 provided “Ontogenetic changes in the skull of Anteosaurus; A. juvenile; B, intermediate sized; C, adult sized, redrawn from Kammerer 2011” (skulls with colored bones in Fig. 2). However, their figure 20 labeled the intermediate sized skull as Titanophoneus (redrawn from Kammerer 2011), even though it is not a close match to the real Titanophoneus (Fig. 2). So they presented a phylogenetic series, not an ontogenetic one. That intermediate skull is not Anteosaurus and neither is the juvenile.

Given the choice of describing
the first known Anteosaurus juvenile skull or just another Australosyodon skull, Kruger 2014 and Kruger et al. 2017 opted for the former.

Figure 3. From Kruger 2014 the parts of BP/1/7074 colorized to show how the bones were 'disarticulated.' This is not disarticulation. This is breakage.

Figure 3. From Kruger et al. 2017 the parts of BP/1/7074 colorized to show how the bones were ‘disarticulated.’ This is not disarticulation. This is disassembly of articulated bones.

More misdirection
The abstract describes the bones as ‘unfused’ and therefore juvenile. However the bones did not come out of the ground separate from one another (Fig. 3) and the bones of Syodon are also unfused as an adult. If the bones are indeed juvenile, then they are related to Australosyodon and Syodon, not Anteosaurus.

Statistics, graphs, CT scans and all the high tech data in the world
won’t help you if you don’t have a phylogenetic analysis as your bedrock. You have to know what you have before you can describe it professionally.

From the conclusion
“The ontogenetic series of Anteosaurus magnifies is represented by skull lengths varying from 280 to 805 mm. The most important morphological modifications of the skull are the development of pachyostosis, the positive allometries of the temporal opening, and the postorbital and suborbital bars, which become increasingly robust in adults (Fig. 21). The anterior portion of the snout also grew relatively faster. Adults show proportionally smaller orbits and an increase in the angle between the nasal and the frontal. On the skull roof, the pineal boss increases in height and there is a greater degree of pachyostosis around it. The cranial morphology of juvenile Anteosaurus appears broadly similar to that of the Russian Syodon.”

From the Kruger thesis
“Only two genera of anteosaurs, Australosyodon and Anteosaurus, are recognised from the Karoo rocks of South Africa.” Once again, phylogenetic analysis brings us to a different conclusion. We have to put away our assumptions until the analysis is complete.

We’ve seen before
how the lack of a rigorous large gamut phylogenetic analysis can affect conclusions.

  1. Liu et al 2013 and Kammerer2011 (listed above) eyeballed their purported juveniles without a large gamut analysis.
  2. Several of Bennett’s papers (listed below) on Pteranodon, Rhamphorhynchus, Pterodactylus and Germanodactylus concluded that specimens were varied due to gender or ontogeny, without testing them phylogenetically.
  3. Hone and Benton 2007, 2009 deleted key taxa, introduced typos into the dataset and switched citations to support their contention that pterosaurs were related to erythrosuchid archosauriforms and Cosesaurus was close to Proterosuchus among many other foibles.
  4. Ezcurra and Butler 2015 lumped several Proterosuchus/Chasmatosaurus specimens together in an ontogenetic series without testing them phylogenetically.
  5. I’m leaving out the many small gamut phylogenetic analyses that suffered from taxon exclusion or inappropriate taxon inclusion that messed up results. Use keyword: ‘taxon exclusion‘ to locate them in this blog.

References
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. 
Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 1994.
 Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea). Occassional Papers of the Natural History Museum University of Kansas 169: 1–70.
Bennett SC 2001. 
The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153
Bennett SC 1995. 
A statistical study of Rhamphorhynchus from the Solnhofen limestone of Germany: year classes of a single large species. Journal of Paleontology 69, 569–580.
Bennett  SC (2012) [2013
] New information on body size and cranial display structures of Pterodactylus antiquus, with a revision of the genus. Paläontologische Zeitschrift (advance online publication) doi: 10.1007/s12542-012-0159-8
Ezcurra MD and Butler RJ 2015. Post-hatchling cranial ontogeny in the Early Triassic diapsid reptile Proterosuchus fergusi. Journal of Anatomy. Article first published online: 24 APR 2015. DOI: 10.1111/joa.12300
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia). Journal of Systematic Palaeontology, 9: 2, 261—304, First published on: 13 December 2010 (iFirst) To link to this Article: DOI: 10.1080/14772019.2010.492645\
Liu J 2013. 
Osteology, ontogeny, and phylogenetic position of Sinophoneus yumenensis(Therapsida, Dinocephalia) from the Middle Permian Dashankou Fauna of China, Journal of Vertebrate Paleontology, 33:6, 1394-1407, DOI:10.1080/02724634.2013.781505
Kruger A 2014. Ontogeny and cranial morphology of the basal carnivorous dinocephalian, Anteosaurus magnifies from the Tapinocephalus assemblage zone of the South African Karoo. Masters dissertation, University of Wiwatersand, Johannesburg.
Kruger A, Rubidge BS and Abdala F 2017. A juvenile specimen of Anteosaurus magnifies Watson, 1921 (Therapsida: Dinocephalia) from the South African Karoo, and its implications for understanding dinocephalian ontogeny. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2016.1276106
Rubidge BS1994. Australosyodon, the first primitive anteosaurid dinocephalian from the Upper Permian of Gondwana. Palaeontology, 37: 579–594.

Four more basal tetrapods added to the LRT

Spoiler alert:
No basic changes to the large reptile tree topology (LRT, Fig. 1, 938 taxa). The biggest difference from traditional trees continues to be the separation of dissorophoids, including Cacops, from temnospondyls. Cacops and kin are still nesting with the lepospondyls, including all microsaurs and extant amphibians

Figure 1. Subset of the LRT showing basal tetrapods. Four more are added here with no change in tree topology.

Figure 1. Subset of the LRT showing basal tetrapods. Four more are added here with no change in tree topology.

Tomorrow or shortly thereafter
I’ll start reporting some numbers and describing some interesting taxa. For those interested, whenever I add taxa, I revisit and update old taxa including their scores. So if you want an updated .nex file, now is a better time than ever, with errors minimized.

 

A bit more about dissorophids and temnospondyls

This all started
a few days ago with some interest by readers in the nesting of dissorophoids (Cacops and kin; Fig. 1) apart from temnospondyls. The large reptile tree (LRT) nested dissorophoids at the base of the lepospondyls, contra traditional studies. I tested this heretical nesting several times over and the nesting is robust. Today we’ll put that nesting to yet another test.

Here’s the problem
Cacops looks like a temnospondyl. It’s big. It has a big head, short torso and tiny tail. It was probably terrestrial, judging by the robust limbs. Even the palate looks like that of a temnospondyl. The question is: can all this be by convergence?

In this case, as in many others…
it’s better not to eyeball it, or play favorites, or follow tradition, but to let the computer decide.

Over the last few days
I’ve been combing the Internet for traditional dissorophid outgroups in the literature. Iberospondylus was one candidate, but it nested only with temnospondyls in the LRT, far from dissorophids.

Figure 1. Cacops and its sisters.

Figure 1. Cacops and some of its sisters.

 

Another, perhaps better candidate  
is Parioxys fericolus (Cope 1878, Carroll 1964; Early Permian). It shares several traits with Cacops, like a big curved squamosal. Cope (1882) later suggested his specimens were actually young Eryops (Fig. 2), but subsequent workers considered Parioxys a separate genus. Moustafa (1955) allied Parioxys with the Dissoroophidae in the super-family Dissorophoidea. Carroll (196) described an earlier and more primitive species (Parioxys bolli, Fig. 3).

Figure 2. Eryops, a temonspondyl, shares many traits by convergence with Cacops (fig. 1). Even the palate is a close match. This is where phylogenetic analysis really shines, separating convergent taxa from close kin.

Figure 2. Eryops, a temonspondyl, shares many traits by convergence with Cacops (fig. 1). Even the palate is a close match. This is where phylogenetic analysis really shines, separating convergent taxa from close kin.

Carroll reports,
“It is primarily on the basis of the configuration of the pelvis and the possession of two pairs of sacral ribs, as well as the lack of a fourth trochanter on the femur, that Moustafa allied Parioxys with the dissorophids.”

Among basal tetrapods, Cacops is atypical in having two sacral ribs, although Eryops has one “true sacral” and another vertebra very much like it. Carroll further notes,

Carroll continues:
“Since the features that Moustafa used to ally the dissorophids with Parioxys have developed separately within the two groups, these characters cannot be cited to indicate close relationship.
 The possession of a posterior proximal ramus of the adductor ridge in P. bolli, and the presence of a fourth trochanter, further separate the genus from dissorophids, which do not show these features even in the later Middle Pennsylvanian genera.”

Figure 3. Parioxys is a temnospondyl sister to Eryops and, despite sharing several traits, is not close to Cacops.

Figure 3. Parioxys is a temnospondyl sister to Eryops and, despite sharing several traits, is not close to Cacops in the LRT. Note the large fourth trochanter below the femur and the long ilium connecting to two sacrals, but covering three. Note the deeply curved squamosal. No complete skeleton is known yet for this genus, so this is a chimaera.  Images compiled from Carroll 1964

After phylogenetic analysis
the dissorophids remain nested at the base of the lepospondyls. Parioxys nested with Eryops. Only with the removal of ALL intervening taxa do dissorophids nest with temnospondyls, and then there is loss of resolution.

With the removal of Parioxys from the dissorophids, the former clade, Dissorophoidea,
now appears to be paraphyletic

Yet another heresy.
I know the basal tetrapod workers don’t like this new insight into temnospondyl and dissorophid relations, or rather the lack thereof. Maybe this will solve some of the problems they’ve been having on their own in phylogenetic analyses.

And add this discovery to the pile
of pterosaur origins, turtle origins, whale origins, snake origins, dinosaur origins, multituberculate origins, bat origins, diadectid origins, reptile origins and many more that the large reptile tree brings insight to. I never thought it would go this far.

As always,
if anyone can produce a taxon or a set of taxa that can attract Cacops and the dissorophids to the temnospondyls, please send them over. I am more than willing to test any serious candidates.

References
Carroll RL 1964. The relationships of the Rhachitomous amphibian Parioxys. American Museum Novitates 2167:1-11.
Cope ED 1878. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. Proc. Amer. Phil. Soc., vol. 17, pp. 505-530.
Cope ED 1882. Third contribution to the history of the Vertebrata of the Permian formation of Texas. Ibid., vol. 20, pp. 447-461.
Moustafa YS 1955. The skeletal structure of Parioxys ferricolus, Cope. Bull. Inst. d’Egypte 36: 41-76.