Patranomodon and descendants

Rubidge and Hopson (1990, 1996) got it right.
Patranomodon (Figs. 1–3) is basal to the dicynodonts AND the venjukovamorphs the Therapsid Skull Tree (TST, 68 taxa; Fig. 4).

FIgure 1. Patranomodon with bones colored here helped to rescuer the taxon. The original drawing omitted the septomaxilla and the anterior rostrum and mandible. Now it really does look more like a basal dicynodont.

FIgure 1. Patranomodon with bones colored here helped to rescuer the taxon. The original drawing omitted the septomaxilla and the anterior rostrum and mandible. Now it really does look more like a basal dicynodont.

Figure 1b. Patranomodon post-crania assembled.

Figure 1b. Patranomodon post-crania assembled.

Rubidge and Hopson (1996) reported, Patranaomodon is primitive with respect to other anornodonts in having short palatal exposure of the premaxilla, an unreduced tabular, a slit-like interpterygoidal vacuity, a screw-shaped jaw articulation (which precludes fore-aft sliding of the lower jaw), and only three sacral vertebrae. The poorly-known Galechirus and Galepus from the younger Cistecephalus Assemblage Zone appear to be at a comparably primitive evolutionary grade, and the three genera are tentatively united in the family Galechiridae. The taxon Dromasauria is shown to be paraphyletic and therefore should be discarded.”

In the TST
both venjukoviamorphs and dicynodonts are large, terrestrial dromasaurs. Here (Fig. 2) are a set of skulls to scale demonstrating the ancestry of the vejukoviamorphs.

Figure 2. Patranomodon and Galeops are sisters, both in the ancestry of dicynodonts and venjukoviamorphs.

Figure 2. Patranomodon and Galeops are sisters, both in the ancestry of dicynodonts and venjukoviamorphs.

This second set of skulls
(Fig. 3) shows the ancestry of the dicynodonts to scale, according to the TST.

Figure 3. The ancestry of dicynodonts includes Patranomodon and Galeops.

Figure 3. The ancestry of dicynodonts includes Patranomodon and Galeops.

A recent look at dicynodonts
(Kammerer 2019) suggested that Biseridens was basal to the clade Dicynodontia, but that cladogram did not test the taxa shown here (Fig. 4).

Figure 4. TST revised with new data on Patranomodon and sister taxa.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

We’ll dive deeper
into Kammerer 2019 in the next few days. Currently I am updating all the data for the TST using photos (Fig. 1) to supplement earlier drawings to fine tune the scoring. Yes, it’s okay to correct earlier errors based on less accurate drawings.


References
Rubidge BS and Hopson JA 1990. A new anomodont therapsid from South Africa and its bearing on the ancestry of Dicynodontia. South African Journal of Science, 86(1), 43-45.
Rubidge BS and Hopson JA 1996. A primitive anomodont therapsid from the base of the Beaufort Group (Upper Permian) of South Africa. Zoological Journal of the Linnean Society, 117: 115–139. Doi:10.1111/j.1096-3642.1996.tb02152.x

wiki/Patranomodon

Lisowicia: Already superlative, so no need to further exaggerate

A new 4.5 meter long Late Triassic dicynodont has been reported.
Lisowicia bojani
(Sulej and Niedzwiedzki 2018, Late Triassic; Fig. 1) is by far the largest dicynodont now known, greatly superseding the previous record holder, Stahleckeria (von Huene 1935; Fig. 1). That’s fantastic all by itself. So why would a world-famous paleontologist and the Smithsonian website further exaggerate this discovery?

Figure 1. Lisowicia compared to extant elephants and the previous largest dicynodont, Stahleckeria.

Figure 1. Lisowicia compared to extant elephants and the previous largest dicynodont, Stahleckeria, not itself a ‘small and unseen’ taxon, but forgotten or omitted in the present storyline. The young lady in the pink tie-dye shirt is five feet tall.

Online Smithsonian Magazine headlines the story:
“Early Mammals Were Thought to Be Small and Unseen in the Age of Dinosaurs. An Elephant-Sized Fossil Complicates That Story — At a time when proto-mammals and other creatures were getting smaller, this dicynodont bulked up with the thunder lizards”

Lisowicia is indeed elephant-sized,
in length, but not height. Lisowicia had shorter legs, like another dicynodont, bear-sized Stahleckeria (Fig. 1). So… while the early and proto-mammals were indeed small, other  ‘creatures’ were also ‘bulking up‘ in the Late Triassic, including dicynodonts, rauisuchians, erythrosuchians, poposaurs, protorosaurs, phytosaurs and proterochampsids, to name only the terrestrial tetrapods. Even in this company, Lisowicia is still extraordinary in size. On the other hand, and let’s be honest about this… in the Late Triassic Age of Dinosaurs, sauropodomorphs were really the only dinosaurs to also bulk up. The rest remained about human-sized or smaller.

Be careful not to create mythology
when discussing dinosaurs. Keep it real.

Author and paleontologist Dr. Stephen Brusatte
(U. of Edinborough) chimed in with this paragraph of inappropriate surprise and hyperbole: “Before these giant bones were discovered, you would have been called crazy if you ever suggested there were giant, elephant-sized mammal cousins living alongside some of the very first dinosaurs,” he says. “We used to think that after the end-Permian extinction [252 million years ago], when some 90-95 percent of all species went extinct, mammals and their relatives retreated to the shadows while dinosaurs rose up and grew to enormous sizes. That’s the story I tell my students in my lectures. But this new discovery throws a wrench into that simple tale.” 

We “used to think” nothing of the sort! 
If you are a student of Dr. Brusatte, find another professor! Dr. Brusatte has been on the wrong end of many paleo hypotheses. Use keyword “Brusatte” in the little white search box above for details on several past subjects ranging from dinosaur origins to footprint identification to multituberculates.

Brusatte also said in ScienceMag.org, “‘Who would have ever thought that there were giant, elephant-sized mammal cousins living alongside some of the very first dinosaurs?’marvels Stephen Brusatte, a vertebrate paleontologist at The University of Edinburgh.” 

Seems Dr. Brusatte is forgetting about Stahleckeria,
the previous record-holder for largest dicynodont at 3.3 meters in length. A taxon that size is definitely not “relatively in the shadows.” If you’re going to speak to the press, don’t omit pertinent details.

Lisowicia is already unique and spectacular
at twice the height of Stahleckeria. So there is no need to exaggerate the truth or reduce the size of comparables in order to make Lisowicia appear even more unique and spectacular. A comparative graphic like the one above would have made the point without the verbal hyperbole, omission and overkill.

Are dicynodonts really mammal cousins?
In the large reptile tree (LRT, 1337 taxa) dicynodonts and other herbivorous basal synapsids (Anomodontia) split from the carnivorous synapsids that led to mammals immediately following the pelycosaurs. So that’s one node. Basal anomodonts are separated from basal mammals by 12 nodes and then add 5 more nodes to get to Lisowicia nesting as a very derived anomodont.  So an inappropriate comparison to basal mammals is likewise stretching science journalism to an uncalled-for degree. If you want to educate the public, educate the public.

Lisowicia deserves some grand-standing.
Let’s just try to keep it real.

References
Sulej T; Niedźwiedzki G 2018. An elephant-sized Late Triassic synapsid with erect limbs. Science: eaal4853. doi:10.1126/science.aal4853
v. Huene F 1935. Lieferung 1. Anomodontia [Part 1. Anomodontia]. Die Fossilen Reptilien des Südamerikanischen Gondwanalandes. Ergebnisse der Sauriergrabungen in Südbrasilien 1928/29 [The Fossil Reptiles of South American Gondwanaland. Results of the Dinosaur Expeditions in southern Brazil 1928/29]. C. H. Beck’sche Verlagsbuchhandlung, München 1-82

https://en.wikipedia.org/wiki/Lisowicia
smithsonianmag.com/smart-news/elephant-size-mammal-cousin-mingled-dinosaurs
https://en.wikipedia.org/wiki/Stahleckeria

Maybe Anomocephalus had canine fangs, too!

Two dicynodont-mimics,
Tiarajudens (UFRGS PV393P, Cisneros et al. 2011) and Anomocephalus (Modesto et al. 1999) were discovered in the last few two decades. Tiarajudens had sharp teeth and a fang/canine/tusk. Anomocephalus had flat teeth and apparently no tusk (Fig. 1).

Working from the published tracing
I put the scattered teeth of Anomocephalus back into the jaws and discovered that maybe there is a tusk/fang in there, too (Fig. 1). If valid, the fang was broken in half during typhonomy, so it became the same length as the other teeth, all of which had narrow roots, unlike the fang.

Figure 1. Anomocephalus in situ and reconstructed. Apparently a fang/canine/tusk was hiding among the broken teeth.

Figure 1. Anomocephalus in situ and reconstructed. In situ image from Modesto et al. 199. Apparently a fang/canine/tusk was hiding among the broken teeth.

Tiarajudens and Anomocephalus
are considered middle Permian primitive herbivorous anomodonts by the author(s) of Wikipedia, who also suggest they were ancestral to dicynodonts. By contrast, the large reptile tree (Fig. 2)  nests Tiarajudens and Anomocephalus in a clade close to, but separate from dicynodonts (Fig. 2).

Figure 3. Basal therapsid tree.

Figure 3. Basal therapsid tree. Note the nesting of the Anomodontia and the dicynodonts here, both derived from smaller dromasaurs.

According to the LRT, the ancestors of dicynodont mimics were 
Venjukovia and Otsheria. The ancestors of dicynodonts include Suminia, a late-survivor of an early radiation. Both were derived from smaller dromasaurs (Fig. 3).

Figure 3. Venjukoviamorphs include the dicynodont mimics, Tiarajudens and Anomcephalus. now with long canines.

Figure 3. Venjukoviamorphs include the dicynodont mimics, Tiarajudens and Anomcephalus, the latter now with mid-length canines. The Anomocephalus drawing is modified from Modesto et al. 1999 and appears to have certain problems.

References
Cisneros, JC, Abdala F, Rubidge BS, Dentzien-Dias D and Bueno AO 2011. Dental Occlusion in a 260-Million-Year-Old Therapsid with Saber Canines from the Permian of Brazi”. Science 331: 1603–1605.
Modesto S, Rubidge B and Welman J 1999. The most basal anomodont therapsid and the primacy of Gondwana in the evolution of the anomodonts. Proceedings of the Royal Society of London B 266: 331–337. PMC 1689688.

The origin and evolution of the Dicynodontia

Figure 1. The origin of the Dicynodontia from basal therapsids. Here Cutleria, Stenocybus, two unnamed taxa, Otsheria, Venjukovia, Eodicynodo and Dicynodon are shown in order along with the major trait that each portrays.

Figure 1. The origin of the Dicynodontia from basal therapsids. Here Cutleria, Stenocybus, two unnamed taxa, Otsheria, Venjukovia, Eodicynodo and Dicynodon are shown in order along with the major trait that each portrays. Click to enlarge. Most basal synapsids are known from skulls. During the evolution of the dicynodonts, the tail became very short and the toes were shorter as well.

Earlier we looked at the origin of dicynodonts and dromasaurs separate from all other synapsids. Here (Fig. 1) are a selection of skulls that demonstrate the evolutionary origin of the very odd skull of Dicynodon, only one of many dicynodonts.

Wikipedia reports
“Dicynodontia is a taxon of anomodont therapsids or synapsids with beginnings in the mid-Permian, which were dominant in the Late Permian and continued throughout the Triassic, with a few possibly surviving into the Early Cretaceous. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means ‘two dog tooth’. They are also the most successful and diverse of the non-mammalian therapsids, with over 70 genera known, varying from rat- to ox-sized.”

Wikipedia also reports
that dicynodonts nested between dinocephalians and gorgonopsians. That is not supported in the large reptile tree as both are quite derived and don’t take into account basal pre-dicynodont taxa.

You can see a number of therapsid skulls in evolutionary order here.

 

Ever wonder about Galepus?

As opposed to the wildly popular bird-like dromaesaurs, the squirrel-like dromasaurs (lacking the “e” in the middle), like Galepus (Fig. 1, Broom 1910) are rarely studied. Brinkman (1981) made an important contribution. These less popular anomodonts are cousins to the hippo-like dicynodonts (Fig. 2). Both were herbivores of the Late Permian, nesting within the Therapsida and Synapsida.

I’ve seen a century-old reconstruction of the skull of Galepus, but I’ve never seen the whole body reconstructed (Fig. 10. That seems a shame as it is represented by a nicely curled nearly complete skeleton at the American Museum of Natural History (hirez color images kindly provided by their staff). And it’s been known for some time now. Much of the skull and skeleton is represented by impressions of missing bone in coarse sandstone.

Figure 1. Galepus, the dromasaur, anomodont, therapsid, reconstructed from the complete skeleton at the AMNH.

Figure 1. Galepus, the dromasaur, anomodont, therapsid, synapsid reconstructed from the complete skeleton #5541 at the AMNH. Wrist and ankle are reconstructed according to patterns seen in Galechirus and Suminia (Fig. 2, wrist and ankle inserts copied above). Note the oversized clavicle here. I’m wondering if I made a misidentification here, or is this taxon just odd that way? The hands are indeed robust with great symmetry, like a mammalian burrower, the mole, also known for its strong forelimbs.

The skull is only a cast of the internal surface of the roofing bones. Well marked, but odd.

Galepus has been nested (ref) with Galechirus close to Galeops at the transition to Eodicynodon (Fig. 3) between dromasaurs + kin and dicynodonts + kin.

Figure 2. Two other dromasaurs, Suminia and Galechirus.

Figure 2. Two other dromasaurs, Suminia and Galechirus. Galepus was close in size. Note the small clavicles here. Those go along with smaller forelimbs and a more asymmetric manus.

However,
The large reptile tree found a different relationship, with dromasaurs + dicynodonts splitting from the other therapsids at the base of that clade. Earlier we looked at differences and similarities between Galeops and Eodicynodon (Fig. 3). While they share many traits, phylogenetic analysis finds more parsimonious relationships when more taxa are introduced. Earlier we also looked at the base of the Anomodontia and the new taxa now nesting there.

Figure 1. Eodicynodon the basal dicynodont and Galeops the derived dromasaur. Did dicynodonts arise from dromasaurs? Not likely according to the large reptile tree which nests Stenocybus as their last common ancestor.

Figure 3. Click to enlarge. Eodicynodon the basal dicynodont and Galeops the derived dromasaur. Did dicynodonts arise from dromasaurs? Despite several convergent traits, not likely according to the large reptile tree which nests Stenocybus as their last common ancestor and recovers other taxa closer to both.

Earlier we looked at Stenocybus nesting at the base of the Anomodontia. Here’s the new synapsid tree (Fig. 4).

Figure 4. Therapsid family tree. Note anomodonts are separate from the other therapsids.

Figure 4. Therapsid family tree. Note anomodonts are separate from the other therapsids. And dromasaurs are distinct from dicynodonts. Stenocybus is their common ancestor. Here sister taxa are more parsimoniously nested. IOW they look more like each other and share more traits.

References
Brinkman D 1981. The Structure and Relationships of the Dromasaurs (Reptilia: Therapsida). Brevioria, 465: 1-34.
Broom R 1910. A comparison of the Permian reptiles of North America with those of South Africa. Bulletin of the American Museum of Natural History 28: 197-234.

Microurania – A rarely studied taxon at the base of the Dicynodonts

Earlier we looked at basal anomodonts, noting that Biseridens should not be part of this inclusion set because it is a basal dinocephalian. Instead Microurania (Fig. 1) and Stenocybus should be included as they nest in that basal position in the large reptile tree.

There are few references for the rarely studied Russian therapsid Microurania (Ivakhnenko 1995, 2003, Middle Permian, Lower Tatarian), and only one illustration that I know of. Yet it is an important transitional taxon leading to the base of the Dicynodontia.

Figure 1. All that is known of Microurania, a basal therapsid, basal anomodont and dicynodont precursor. Image from Ivakhnenko 2003.

Figure 1. All that is known of Microurania, a basal therapsid, basal anomodont and dicynodont precursor. Image from Ivakhnenko 2003.

Close to Stenocybus and Nikkasaurus at the base of the Therapsida, the proto-dicynodont Microurania (Fig. 1) retained upper and lower single canines. It was considered a biarmosuchian but nests in the therapsid subset of the large reptile tree closer to Otsheria and Venjukovia {now Ulemica] (Fig.1) at the base of the Anomodontia.

The holotype (PIN 4337/1) is a partial skull with leaf-like postcanine teeth similar to those in Phthinosuchus.

Microurania has a shorter snout than Biarmosuchus, closer to Stenocybus with which it shares procumbent teeth. Microurania retained canines, unlike Nikkasaurus.

Figure 2. Basal therapsids and sisters to their ancestors. The short skull of Stenocybus is retained by anomodonts like Microurania.

Figure 2. Basal therapsids and sisters to their ancestors. The short skull of Stenocybus is retained by anomodonts like Microurania, dromasaurs and dicynodonts. This also demonstrates the present diphyletic therapsids with two lineages arising from basal ophiacodonts.

Figure 4. Basal therapsid family tree. Biseridens nests far from the anomodonts and Microurania.

Figure 4. Basal therapsid family tree. Biseridens nests far from the anomodonts and Microurania.

Plain Jane/Brown Sparrow
Microurania is one of those plain Jane / brown sparrow unspectacular sorts of reptiles. Frankly, it looks kind of boring. The ironic reality is, such “generic” taxa are exactly where evolution is making key transitions. They are blends, hybrids,  part this and part that.

Microurania does not have the elevated suborbital/cheek region found in Otsheria, Venjukovia [now UIlemica] and Eodicynodon. The large canines found in dicynodonts may be new traits. Immediate predecessors do not have such large canine teeth.

The Therapsida may turn out to be essentially diphyletic. Stenocybus and the Anomodontia form one branch. Nikkasaurus and the rest of the Therapsida (including mammals) form the other branch. Ophiacodon is currently the most completely known common ancestor, but two scrappy double-canine taxa may be transitional forms.

References
Ivakhnenko MF 1995. New primitive therapsids from the Permian of Eastern Europe, Paleontol. Zh. 1995(4):110–119.
Ivakhnenko MF 2003. Eotherapsids from the East European Placket (Late Permian). Paleontological Journal, 37, Suppl. 4: S339-S464.

 

New Anomodont Family Tree (Ruta et al. 2013)

A new family tree of the anomodonts (dicynodonts + dromasaurs and their common ancestors) has just come out (Ruta et al. 2013) and I’m sure it’s a good tree — except maybe at the base. A few taxa are missing and one seems to be added that should not be included.

Figure 1. Below: New anomodont tree from Ruta et. al. 2013. Above: Basal anomodonts found by the large reptile tree. Biseridens (in purple) nests as a basal dinocephalian in the large reptile tree. Taxa in green nest together as dromasaurs. Taxa in magenta nest together in the Dicynodontia and their predecessors. The other taxa are derived genera not considered in the large reptile tree.

Figure 1. Below: New anomodont tree from Ruta et. al. 2013. Above: Basal anomodonts found by the large reptile tree. Biseridens (in purple) nests as a basal dinocephalian in the large reptile tree. Taxa in green nest together as dromasaurs. Taxa in magenta nest together in the Dicynodontia and their predecessors. The other taxa are derived genera not considered in the large reptile tree.

Delete Biseridens at the root. Add Stenocybus and Microurania.
The rooting of the Ruta et al. (2013) tree on Biseridens may be an error. The large reptile tree graphically portrayed with therapsid skulls found Biseridens to nest at the base of the Tapinocephalia. In the large reptile tree the root of the anomodont tree goes back to Stenocybus (Fig. 1, itself considered a juvenile dinocephalian by professional paleontologists). The short skull of this clade is distinct from the longer skull of biarmosuchids and their many descendants on the other branch of the Therapsida.

Dromasaurs like Suminia (Fig.1) and Anomocephalus (fig. 1) have a particular affinity to Stenocybus due to direct descent. You can see the complete and enlarged basal therapsid skull tree here.

Dicynodonts, like Eodicynodon (Fig. 1) follow a little-studied genus, Microurania, which needs a post of its own soon.

Galeops, a toothless dromasaur, is the transitional taxon leading to dicynodonts in the Ruta et al. (2013) tree. Here (Fig. 3) Galeops nests as a derived dromasaur, having lost teeth in convergence with dicynodonts.

Figure 2. Basal therapsids and sisters to their ancestors. The short skull of Stenocybus is retained by anomodonts like Microurania.

Figure 2. Basal therapsids and sisters to their ancestors. The short skull of Stenocybus is retained by anomodonts like Microurania. The long skull of Nikkasaurus is reflected in Biarmosuchus. Both had very large eyes and a smaller size overall. 

The lack of canines in Nikkasaurus indicates there is probably an unknown sister to Nikkasaurus that retained canines and that Nikkasaurus will probably someday nest as an odd tiny-tooth therapsid offshoot from the major families.

 

Figure 4. Basal therapsid family tree. Biseridens nests far from the anomodonts and Microurania.

Figure 3. Basal therapsid family tree. Biseridens nests far from the anomodonts and Microurania. Anomodonts may have had a distinct origin apart from the rest of the Therapsida. 

A Diphyletic Therapsida?
The therapsid family tree indicates a monophyletic Therapsida with a basal division having Stenocybus basal to anomodonts and Nikkasaurus basal to all other therapsids. Ophiacodon is their most recent common ancestor. The interesting thing is Nikkasaurus and Biarmosuchus (Fig. 2) look more like the more basal long-snouted Archaeothyris in overall view. On the other hand, Stenocybus looks more like the derived short-snouted Haptodus in overall view. This makes one wonder if the Therapsida had two origins with anomodonts arising from the Ophiacodon / Haptodus transition at the base of the Sphenacodontia. The remaining Therapsids appear to have had origins at the Archaeothryis / Ophiacodon transition.

I think we’ll have proof of this someday. The hints are strong.

References
Ruta M, Angielczyk KD, Fröbisch J and Benton MJ 2013. Decoupling of morphological disparity and taxic diversity during the adaptive radiation of anomodont therapsids. Proceedings of the Royal Society B (Biological Sciences) online here. Supp material here.

Reconstructing the Skull of Stenocybus

Stenocybus accidentusis (Cheng and Li 1997) is known from a skull and a set of skull parts. Earlier we looked at comparisons to anteosaurs as reported by Kammerer (2011).

The holotype specimen, IGCAGS V 361, is complete, but skewed parasagittally. Photographs of the specimen (Kammerer 2011), my only data source were taken from less than ideal angles using a fairly wide angle lens (which does not flatten perspective). Unfortunately Kammerer (2011) did not delineate the bones, so I attempted to differentiate sutures from cracks. So, based on observation and comparison with potential sister candidates, here they are (having never seen the actual fossil). If I made any mistakes, please bring them to my attention. I certainly made mistakes earlier. This is a learning process. The parietal portion was particularly troublesome as the posterior frontals have a medial hole into which the preparietal snakes. Moreover the parietal was unexpectedly narrow. Nevertheless, it all seems to fit together and no “rules” were broken.

Stenocybus in situ

Figure 1. Stenocybus in situ with bones identified. Colors match those in figure 2. A longer lens (not such a wide angle) and a more direct lateral and dorsal view would have made reconstruction much easier to do. From Kammerer 2011.

 

Figure 2. Stenocybus reconstructed based on tracings in figure 1. Note the lacrimal AND septomaxilla in close proximity to each other.

Figure 2. Stenocybus reconstructed based on tracings in figure 1. Note the lacrimal AND septomaxilla in close proximity to each other.

Overall
The skull has the appearance of a small Haptodus retaining traces of its ophiacodontid ancestry. There is a median ridge on the skull.

Premaxilla
The ascending process remains long, as in ophiacodontids and most therapsids, but unlike sphenacodontids.

Lacrimal and Septomaxilla
Both appear side by side here, the latter external and the former internal, their plesiomorphic positions. One traditional trait separating pelycosaurs from therapsids is the septomaxilla becomes a surface (dermal) bone in therapsids. This can be seen to be happening in Stenocybus with the lacrimal retreating.

Preparietal
This new bone makes an early appearance in Stenocybus. Not sure why, but it appears to occupy a circular foramen in the posterior frontal, just anterior to the parietal foramen, which is relatively small here, as is the parietal itself.

Maxilla
This upper tooth bearing bone contacts the nasal and prefrontal. A tiny sliver of no consequence extends beneath the orbit.

Quadratojugal and Squamosal
Ophiacodonts have a horizontal quadratojugal. Sphenacodonts hide their’s beneath a squamosal. Therapsids have a vertical quadratojugal, sometimes visible, often not. Stenocybus shows the transitional stage, somewhat of a diagonal orientation, somewhat hidden by the squamosal. The squamosal is also overtaking the posterior jugal.

Supratemporal
Pelycosaurs have them. Therapsids don’t. Here they are found as flaked off loose elements near the parietal foramen. So they were of little consequence and probably disappeared rather than fusing to the squamosal.

Teeth
The anterior teeth of Stenocybus are rake-like. Does this indicate the start of an herbivorous diet? If so, perhaps the earliest stages of one.

Angular
In therapsids the posterior angular separates itself from the body of the mandible and develops a retroarticular process. We don’t see much separation here in Stenocybus.

Palate
The choanae are elongated here, shifting the pterygoid and palatine bones largely behind the tooth row, which presages the condition in anomodonts. However the ventral view of the palate remains quite narrow, as in ophiacodonts. The pterygoid transverse processes are vestiges. Palatal teeth were relatively larger. The epipterygoid was reduced to a slim buffer between the jawline and palate.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again. 

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Cheng Z and Li J 1997. A new genus of primitive dinocephalian – the third report on Late Permian Dashankou lower tetrapod fauna. Vertebrata PalAsiatica 35 (1): 35-43. [in Chinese with English summary]
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia), Journal of Systematic Palaeontology, 9: 2, 261 — 304, First published on: 13 December 2010 (iFirst)

wiki/Stenocybus

Biseridens: at the Base of the Anomodontia? No.

A recent Journal of Vertebrate Paleontology Memoire provided much needed and appreciated insight into the speciation of Dicynodon (Kammerer, Angielczyk and Fröbisch 2011), the dicynodont that gave its name to the clade. In their excellent phylogenetic analysis of the dicynodontia, these authors unfortunately placed Biseridens (Liu et al. 2009) at the base.

Testing That Nesting
In a study of basal therapsids, including many not considered by Kammerer, Angielczyk and Fröbisch (2011), Biseridens nested between Syodon and Titanophoneus, not at the base of the Dicynodontia. At the base of the Dicynodontia we find Nikkasaurus, Niaftasuchus, Microurania and Tiarajudens preceding Dicynodon (Fig. 1). That means the tusks of dicynodonts were secondarily developed after loss in earlier and more basal taxa.

The family tree of the Therapsida including the Dicynodontia.

Figure 1. The family tree of the Therapsida including the Dicynodontia. Click to enlarge. Note the position of Biseridens prior to Titanophoneus and Jonkeria, two taxa not tested in the Dicynodon study. Other pertinent taxa excluded from the Kammerer et al. (2012) study include: Nikkasaurus, Niaftasuchus, Microurania and Tiarajudens.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data

References
Kammerer CF, Angielczyk KD and Fröbisch NJ 2011. A comprehensive taxonomic revision of Dicynodon (Therapsida, Anomodontia) and
its implications for dicynodont phylogeny, biogeography, and biostratigraphy. Journal of Vertebrate Paleontology 31, Supplement 1: 1-158
DOI:10.1080/02724634.2011.627074
Liu J, Rubidge B and Li J 2009. A new specimen of Biseridens qilianicus indicates its phylogenetic position as the most basal anomodont. Proceedings of the Royal Society B 277 (1679): 285–292.

wiki/Biseridens

The Origin of the Dicynodonts

Updated Nov. 16, 2013
Dicynodonts were herbivorous therapsids that lost most of their teeth, save the canine fangs. They originated during the Middle Permian (265 mya) and continued at least until the Late Triassic (215 mya), but a specimen from Australia may extend that to the Early Cretaceous (105 mya). Fossils are found world wide.

Anomodonts (including dicynodonts) had a distinct front-back sliding movement of the mandible that affected the development of jaw muscles and the bones that anchored them.

Traditional Dicynodont Origins
Dr. Kenneth D. Angielczyk reported online* that dicynodonts descended from Cynodonts + Therocephalians and the following non-dicynodont anomodonts: Biseridens, Anomocephalus, Venjukovioidea, Patranomodon and Galeops, in order of increasing similarity to dicynodonts. Eodicynodon is considered the most basal dicynodont.

Problem?
It seems difficult to derive anomodonts from the hypercarnivorous therocephalians. Moreover, several basal taxa were not included in the Angielczyk tree.

(*Sorry this was unavailable when I composed this earlier. I’ll keep looking for it.) There’s also the Rubidge Sidor tree here.

Figure 1. Click to enlarge. Basal therapsids in phylogenetic order as shown by their skulls.

Figure 1. Click to enlarge. Basal therapsids in phylogenetic order as shown by their skulls.

Heretical Dicynodont Origins
The large phylogenetic analysis included a larger number of basal therapsids and recovered anomodonts (including dicynodonts) nesting separate from therocephalians and biarmosuchians, at the base of the therapsida. Here (Fig. 1) the basal dicynodont, Eodicynodon, descended from sisters to , Venjukovia, Otsheria, Microurania, IVPP V18120, Stenocybus and Ophiacodon in order of increasing distance. None of these were hyper-carnivores. The non-dicynodont anomodonts, Anomocephalus, Suminia, Venjukovia [now Ulemica], Galechirus and Patranomodon, also descended from a sister to Stenocybus (Fig. 1).

The New Dicynodont Ancestors and the Reappearance of Canine Fangs
While Archaeothyris, one of the oldest synapsids yet discovered, had moderate canine fangs. Ophiacodon had relatively smaller fangs and Nikkasaurus had no trace of fangs. In Microurania (Ivakhnenko 2003) small canine fangs reappeared. Non-dicynodont anomodonts, such as Anomocephalus and Suminia had no fangs. The tusks of Tiarajudens appear to be new structures, further back from the typical canine position. Similarly, the large canine teeth of dicynodonts appear after a reduction of the canines in ancestral taxa.

References
Ivakhnenko MF 2003. Eotherapsids from the East European Placket (Late Permian). Paleontological Journal, 37, Suppl. 4: S339-S464.
Kammerer CF and Angielczyk KD 2009. A proposed higher taxonomy of anomodont therapsids. Zootaxa 2018:1–24.