Pseudotherium enters the LRT

From the Wallace et al. 2019 abstract:
“We describe a new probainognathian cynodont, Pseudotherium argentinus, from the early Late Triassic Ischigualasto Formation of Argentina.”

Figure 1. Pseudotherium from Wallace, Martinez and Rowe 2019, eyeball, premaxilla and mandible from sister Haldanodon added here. Isn’t nice to see all the bones colored? Isn’t that helpful! Note the gave the squamosal and jugal the same color. Best not to do that. 

In the large reptile tree (LRT, 1559 taxa) Pseudotherium (Fig. 1) nests between Haldanodon and Pachygenelus, pretty close to where Wallace et al. nest their new taxon (Fig. 2). Haldanodon is not mentioned in their text. All are descendants of probainognathian cynodonts, so they nailed it! As noted by the authors, the 3D skull of Pseudotherium adds greatly to the dataset of a typically crushed bunch of sister taxa.

Figure 2. Cladogram from Wallasc, Martinez and Rowe 2019. Pink arrow added where LRT nests Pseudotherium. Try to make sure that all basal taxa are to the left (above here). Adding taxa puts Brasilitherium to the Mammalia and Pseudotherium closer to the missing Haldanodon.

Wallace et al. report,
“Our analysis found weak support for Pseudotherium as the sister taxon of Tritylodontidae.”

Not true according to the LRT. More basal in the LRT.

Wallace et al. also report,
“Thus, Pseudotherium may lie just inside or just outside of Mammaliamorpha, and there is also weak character support for its sister taxon relationship with Brasilitherium.”

Not true according to the LRT where Brasilitherium lies in the ancestry of the platypus, Ornithorhynchus, within the Prototheria, within the Mammalia. Pseudotherium nests basal to Pachygenelus in the LRT.

FIgure x. From the Don Prothero lab. They don’t use the LRT which works and we know why: taxon inclusion. 

This was an excellent paper, with lots of details.
Adding a few more taxa would have helped, but just a little.

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References
Wallace RVS, Martinez R and Rowe T 2019. First record of a basal mammailiamorph form the early Late Triassic ischigualasto Formation of Argentina. PLoS ONE 14(8): e0218791. https://doi.org/10.1371/journal.pone.0218791

Dvinia enters the TST

Not to be confused with Dvinosaurus (a basal tetrapod)…
Dvinia (Fig. 1) is a rabbit-sized chiniquodontid cynodont with a fang-pierced rostrum and a high cranial crest.

Figure 1. From Amalitskii 1922, Dvinia skull and mandible from various views slightly larger than actual size.

Dvinia prima (Amalitskii 1922; Late Permian, 254mya; 7 cm skull) nests between Chiniquodon and Pachygenelus in the Therapsid Skull Tree (TST, 69 taxa). The lower canine fit into a maxillary opening. The molars had a circle of cusps around a single large cusp. The postorbital is very tiny, a vestige that would be lost in derived taxa, like basal mammals and Pachygenelus. The lateral temporal fenestrae were huge housing strong jaw muscles, divided by a narrow crest in which a smal brain was located.

Ivakhenko 2013 reported:
“The study of the skull of the Late Permian cynodont Dvinia prima Amalitzky, 1922 shows a combination of the general primitive skull design (many incisors, preservation of the precanine and large interpterygoid fenestra, etc) with the development of a number of “advanced” features (expansion of the temporal fenestra, development of the parietal crest, and closed pineal foramen, unusual structure of the premaxilla, complicated postcanines, and reduction of the angular wing). Dvinia prima is treated as a specialized omnivore and assigned to the family Dviniidae Sushkin, 1928 of the superfamily Thrinaxodontoidea Seeley, 1894.”

Double canines
sometimes appear in theriodonts (gorgonpopsids, therocephalians, cynodonts) and other synapsids. The second is a replacement canine, so it is not a trait one can score in phylogenetic analysis.

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Sidenote:
My computer was in the shop for about 48 hours Friday and Saturday after downloading a virus originating from .tk (Tokelau, a territory of New Zealand located in the South Pacific famous for free domain registry and malicious web masters) that I downloaded when I clicked on a Facebook video that was supposed to show a sperm whale rotating underwater along with a diver. Do not click on that video.

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References
Amalitskii VP 1922. Diagnoses of the new forms of vertebrates and plants from the upper Permian of North Dvia: Bulletin de l’Académie des Sciences de l’URSS, Math and Natural Sciences, 1922, p. 329-340. and in Izv. Ross. Akad. Nauk, Ser. 6 25 (1), 1–12.
Ivakhnenko MF 2013. Cranial Morphology of Dvinia prima Amalitzky (Cynodontia, Theromorpha). Paleontological Journal 47( 2): 210–222. © Pleiades Publishing, Ltd., 2013. Original Russian Text published in Paleontologicheskii Zhurnal, 2013, No. 2:81–93.

wiki/Dvinia

Therocephalians evolved to smaller size? Large Carnivora did not?

Brocklehurst 2019 reports,
“If these results are reliable, they support the traditional paradigm that therocephalians originated as large predators, and only later evolved small body sizes. The patterns observed in mammals do not appear to apply to therocephalians. Mammalian carnivores, once they have reached large size and a specialized bauplan, are apparently unable to leave this adaptive peak. Therocephalians, on the other hand, retreated from the hypercarnivore niche and evolved small sizes later in the Permian.”

Figure 1. Cladogram from Brocklehurt 2019, colors added. Lycosuchus, listed as a basal therocephalian by Brocklehurst, also nests close to cynodonts in the TST. No gorgonopsids are shown here. Biarmosuchus is the outgroup taxon here, a more distant outgroup taxon in the TST.

Brocklehurst’s cladogram
posits that Therocephalia and Cynodontia arose as sisters from a last common ancestor: Biarmosuchus. In the therapsid skull tree (TST, 67 taxa, Fig. 4), Therocephalia (including Cynodontia) arises from Gorgonopsia (Fig. 2).

Figure 2. Gorgonopsids, therocephalians and cynodonts to scale.

The question arises,
what is a ‘large size’ member of the Carnivora? Certainly big cats and walruses (Fig. 3) fall into this definition and do not give rise to smaller ancestors, as Brocklehurst notes. However, if the basalmost member of the Carnivora, Vulpavus, is considered ‘large’ then it breaks the ‘rule’ because it has smaller descendants in the LRT: Mustela and Procyon (Fig. 3). Talpa, the mole, is the smallest member of the Carnivora in the LRT. Talpa has been traditionally omitted from Carnivora studies while being wrongly lumped with the unrelated shrew, Scutisorex, instead.

Figure 3. Carnivora to scale. Note: one branch does increase in size over time (ignoring toy poodles for the moment), while another branch, the one leading to Talpa the mole, shrinks in size. Brocklehurst is correct: once carnivores achieved large size, few to no examples of phylogenetic miniaturization appear in the fossil record.

I wish Brocklehurst 2019 had added
a few sample reconstructions to scale to help readers visualize the size ranges that he found in his cladogram. After all, the subject was ‘size’. I was unfamiliar with the vast majority of therocephalian taxa in his cladogram (Fig. 1).

Figure 4. TST revised with new data on Patranomodon and sister taxa. Here the therocephalian, Bauria, nests closer to cynodonts than in Brocklehurst 2019 (Fig. 1).

Brocklehurst is correct:
once carnivores achieved large size (Fig. 3), no examples of phylogenetic miniaturization subsequently appear. Brocklehurst contrasted this with therocephalians, presuming that Lycosuchus (Fig. 2) was a basal therocephalian, rather than a basal cynodont by definition.

Remember:
Hopson and Kitching 2001 defined  Cynodontia as the most inclusive group containing Mammalia, but excluding Bauria. In the TST (Fig. 4) Abdalodon and Lycosuchus nest on the cynodont side of Bauria.

In the TST
(Fig. 4), cynodonts show no strong size trends until mammals, like Megazostrodon (Fig. 2), evolved tiny sizes. Therocephalians likewise show no strong size trends either (but then, I have not measured every taxon in the Brocklehurt cladogram, Fig. 1). Those that also appear in the TST are in white boxes, and they appear in several clades within Therocephalia.

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References
Brocklehurst N 2019. Morphological evolution in therocephalians breaks the hyper carnivore ratchet. Proceedings of the Royal Society B 286: 20190590. http://dx.doi.org/10.1098/rspb.2019.0590

Kammerer 2019 nests a new dicynodont

Figure 1. Partial cladogram of the Anomodontia (including Dromasauria) and Dicynodontia from Kammerer 2019. Blue taxa are proximal outgroups in this cladogram.

In a description of a new dicynodont, Thliptosaurus,
Kammerer 2019 presented a comprehensive cladogram of the dicynodonts, the dromasaurs and several outgroup taxa (Fig. 1), including the dinocephalians, Biseridens (Fig. 2), Archaeosyodon and Titanophoneus.

Figure 2. Biseridens and Phthinosuchus, two related therapsids. According to Kammerer 2019, Biseridens is the proximal outgroup to the Anomodontia, who’s

Unfortunately 
Kammerer 2019 excluded several outgroup and ingroup taxa pertinent to the origin of dicynondonts and anomodonts. In the Therapsid Skull Tree (TST,  67 taxa, Fig. 4), the Anomodontia (dicynodonts, dromasaurus and kin) arise from basalmost therapsids, like Cutleria, Stenocybus (Fig. 3) and Hipposaurus. These appear prior to Biarmosuchus. Elsewhere on the cladogram, Biseridens and Titanophoneus arise from more derived tapinocephalids unrelated to basal Anomodontia, more distant descendants of Biarmosuchus.

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

Kammerer 2019 was attempting to produce a cladogram
of the clade Anomodontia. I cannot comment on the tree topology of dicynodonts, because the TST includes so few of them. However, Kammerer followed tradition by including Biseridens and Titanophoneus as outgroup taxa, omitting those recovered by the LRT and TST.

So… taxon exclusion
put a small damper on an otherwise comprehensive report. This happens way too often in paleontology.

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

Biseridens (Fig. 2) was too distinct
to be the ancestor to the tiny dromasaurs, Suminia and Galepus (Fig. 3) and the rest of the Anomodontia. The taxa shown above (Fig. 3) demonstrate a more gradual accumulation of traits, better modeling deep time events.

Yesterday we looked at the uncontroversial key role
two small dromasaurs, Patranomodon and Galeops (Fig. 3), played in the origin of the Dicynodontia. Kammerer’s tree and the TST are in agreement on that point. Likewise the two trees agree that Eodicynodon is the basalmost dicynodont and that Suminia is closely related to Otsheria + Ulemica, close relatives of Venjukovia.

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References
Kammerer CF 2019. A new dicynodont (Anomodontia: Emydopoidea) from the terminal Permian of KwaZulu-Natal, South Africa. Palaeontologia africana 53: 179–191. ISSN 2410-4418.

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 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.

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.

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.

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.

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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

Hipposaurus moves to the base of the Anomodontia

New data,
a photograph, of the skull of Hipposaurus (Figs. 1, 2; Haughton 1929; WB123), moved this basal therapsid to the base of the Anomodontia (Fig. 3), one node down (more primitive) in the therapsid skull tree (TST, 67 taxa, Fig. 3) and the same in the large reptile tree (LRT, 1440 taxa).

Figure 1. Hipposaurus skull with colors applied and used to create reconstruction on the right. Note the squamosal is largely missing and splinters of bone fill the orbit. Here those splinters are used to recreate a standard squamosal for this clade.

Wikipedia reports,
Broom 1932 considered Hipposaurus a gorgonopsian in the family ‘Ictidorhinidae’. Ictidorhinus nests between Hipposaurus and the gorgonopsians in the TST (Fig. 3). So, for 1932, and prior to the advent of software-driven cladograms, that was a good assessment.

Figure 2. Published material on Hipposaurus permits one to create a reconstruction like this. Not far removed from its ophiacodont / haptodine / pelycosaur precursors, Hipposaurus had longer, more gracile limbs and a distinct sabertooth canine, like Haptodus or Cutleria on steroids!

Hipposaurus boonstrai (Haughton 1929, skull length 21cm, length 1.2m) Capitanian, Mddle Permian ~260 mya is a basal therapsid. Derived from a sister to  Cutleria, Hipposaurus phylogenetically preceded the Anomodontia and all higher predatory synapsids, including mammals.

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

Much larger than its ancestors, 
Hipposaurus kept the small round skull of its ancestors, but had longer, more slender limbs capable of a more erect pose and probably a faster gait.

Earlier we looked at Dimetropus tracks that were originally attributed to a high-walking Dimetrodon, but fits Hipposaurus those tracks much better. The basalmost therapsid, Cutleria (Lewis and Vaughn 1965; Early Permian) is another possibility known from fewer bones.

Figure 4. Hipposaurus to scale with related taxa. Cutleria is the basalmost therapsid. Stenocybus and the IVPP specimen are also basal anomodonts.

The relatively larger size of the WB 123 specimen skull of Hipposaurus
indicates it was a later, larger variety of the as yet unknown last common ancestor of anomodonts and kynodonts (Fig. 4).

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References
Boonstra LD 1952. Die Gorgonospier-geslag Hipposaurus en die familie Ictidorhinidae: Tydskr. Wet. Kuns 12:142-149.
Broom R 1932. The mammal-like reptiles of South Africa and the origin of mammals. Witherby, London, 376 pp.
Haughton SH 1929. On some new therapsid genera: Annals of the South African Museum 28(1):55-78.
Lewis GE and Vaughn PP 1965. Early Permian Vertebrates from the Cutler Formation of the Placerville Area Colorado. United States Geological Survey Professional Papers 503-C:1-50.

wiki/Hipposaurus

Tiny Abdalodon: a basal cynodont, drags in Lycosuchus

Today’s blogpost returns to basal Therapsida,
after several years of ignoring this clade.

Kammerer 2016 reidentifies an old Procynosuchus skull 
as an even more basal cynodont, now named Abdalodon (Fig. 1). The problem is: cynodonts arise from basal theriodonts (Therocephalia) and Abdalodon nests with another flat-head taxon, Lycosuchus (Fig. 1), a traditional therocephalian in every other cladogram, but not the Therapsid Skull Tree (TST, 67 skull-only taxa, Fig. 2), a sister cladogram to the LRT.

So, where is the cynodont dividing line?
(= which tested taxon is the progenitor of all later cynodonts and mammals?)

It would help if we knew the phylogenetic definition
of Cynodontia because we should never go by traits (which may converge), but only by taxon + taxon + their last common ancestor and all descendants to determine monophyletic clades.

From the Kammerer 2016 abstract:
“Phylogenetic analysis recovers Abdalodon as the sister‐taxon of Charassognathus, forming a clade (Charassognathidae fam. nov.) at the base of Cynodontia. These taxa represent a previously unrecognized radiation of small‐bodied Permian cynodonts. Despite their small size, the holotypes of Abdalodon and Charassognathus probably represent adults and indicate that early evolution of cynodonts may have occurred at small body size, explaining the poor Permian fossil record of the group.”

Figure 1. Abdalodon nests with the many times larger therocephalian Lycosuchus in the LRT.

Hopson and Kitching 2001 defined  Cynodontia
(Fig. 2) as the most inclusive group containing Mammalia, but excluding Bauria. In the TT Abdalodon nests with Lycosuchus on the cynodont side of Bauria.

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

So that makes Lycosuchus a cynodont,
by definition.

Figure 3. Procynosuchus, a basal cynodont therapsid synapsid sister to humans in the large reptile tree (prior to the addition of advanced cynodonts including mammals). This skull has been overinflated dorsoventrally based on the preserved skull, which everyone must have thought was crushed in that dimension.

Earlier we looked at
some Wikipedia writers when they stated, “Exactly where the border between reptile-like amphibians (non-amniote reptiliomorphs) and amniotes lies will probably never be known, as the reproductive structures involved fossilize poorly…” 

Contra that baseless assertion,
with phylogenetic analysis and clades defined by taxa it is easy to determine which taxa are the last common ancestors, sisters to the progenitors of every derived clade in the TT, LRT or LPT. We can tell exactly which taxon was the first to lay amniotic eggs, without having direct evidence of eggs, simply because all of its ancestors in the LRT laid amniotic eggs. In the same way, we can figure out which taxon, among those tested, is the basalmost cynodont. Adding Bauria to the LRT made that happen today.

Let’s talk about size
The extreme size difference between Abdalodon and Lycosuchus (Fig. 1) brings up the possibility of cynodonts going through a phylogenetic size squeeze… retaining juvenile traits into adulthood… neotony… essentially becoming sexually mature at a tiny size for more rapid reproduction, reduced food needs, ease in finding shelters, etc. We’ve seen that before in several clades here, here and here, to name a few.

Figure 4. Charassognathus does not share more traits with Abdalodon than other taxa, like Bauria and Promoschorhynchops in the TT.

Kammerer 2016 mentioned another small taxon,
Charassognathus (Fig. 4). In the TST (Fig. 2) Charassognathus nests with Bauria and Promoschorhynchops, within the Therocephalia, distinct from, and not far from Abdalodon and the Cynodontia. So no confirmation here for Kammerer’s proposed clade, ‘Charassognathidae’ (see above).

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References
Hopson JA and Kitching JW 2001. A Probainognathian Cynodont from South Africa and the Phylogeny of Nonmammalian Cynodonts” pp 5-35 in: Parish A, et al.  editors, Studies in Organismic and Evolutionary biology in honor of A. W. Crompton. Bullettin of the Museum of Comparative Zoology. Harvard University 156(1).
Kammerer CF 2016. A new taxon of cynodont from the Tropidostoma Assemblage Zone (upper Permian) of South Africa, and the early evolution of Cynodontia. Papers in Palaeontology 2(3): 387–397. https://doi.org/10.1002/spp2.1046

wiki/Bauria
wiki/Abdalodon
wiki/Lycosuchus

Hipposaurus: close to the ancestry of man, but off a wee bit

Figure 1. Therapsida includes the pangolin, Manis, which nests here with Notharctus. one of only a few mammals tested so far.

At the very base of the Therapsida
(Fig. 1) we have a split between the plant-eating Anomodontia (dicynodonts, dromasaurs and kin) and the meat-eating Kynodontia (new name for a new clade that encompasses all other therapsids, including cynodonts and mammals). At the base of the Kynodontia is the rarely discussed, but obviously important taxon, Hipposaurus boonstrai (Fig. 2, Haughton 1929, 21 cm skull. SAM 8950). Biarmosuchus is a sister.

Figure 2. Published material on Hipposaurus permits one to create a reconstruction like this. Not far removed from its ophiacodont / haptodine / pelycosaur precursors, Hipposaurus had longer, more gracile limbs and a distinct sabertooth canine, like Haptodus or Cutleria on steroids!

Long-legged, saber-toothed Hipposaurus
was originally thought to be a gorgonopsian, but in a note from Dr. Jim Hopson  (U Chicago) who xeroxed Boonstra 1965 for me, Hipposaurus (“horse lizard”) has been considered a biarmosuchian within the Ictidorhinidae since the 1980s.

Figure 3. The skull of Hpposaurus was larger than that of its sisters and predecessors among the basal Therapsida, including Stenocybus and Cutleria. The fangs were longer too.

There are some odd details
in the manus and pes of this mid-sized carnivore that indicate this is a derived late survivor of an earlier radiation.

1. Hipposaurus has a large pisiform (post axial carpal, Fig. 1)
2. The first centrale is quadrant shaped
3. The second centrale is shaped like a squat chevron
4. The radiale is twice as long as wide
5. The fourth and fifth carpals are fused
6. A small circular sternum present (none in sister taxa)
7. The posterior calcaneum has a hook like tuber
8. Two wedge-shaped centralia extend the width of the tarsus
9. The first distal tarsal is the size of a metatarsal and shifts the proximal metatarsal distally, almost to the mid length of metatarsal 2.
10. Two mid phalanges are fused on pedal digit 4

Speaking of oddities at clade bases…
as we’ve seen before, clade bases are, by definition, when novelties arise. In the case of Hipposaurus, these novel carpal and tarsal oddities went nowhere. A sister taxon without such novelties, Biarmosuchus, produced all the descendants we all know and love. Hipposaurus became a mere footnote and a short Wikipedia page.

References
Boonstra LD 1952. Die Gorgonospier-geslag Hipposaurus en die familie Ictidorhinidae: Tydskr. Wet. Kuns., v. 12, p. 142-149.
Boonstra LD 1965. The girdles and limbs of the Gorgonopsia of the Taphinocephalus Zone. Annals of the South African Museum 48:237-249.
Haughton SH 1929. On some new therapsid genera: Annals of the South African Museum, v. 28, n. 1, p. 55-78.

Biseridens and Phthinosuchus – two misunderstood therapsids

Biseridens, according to Wikipedia,
“is the most basal genus of anomodont therapsid.”

Not so,
according to the large reptile tree (Fig. 3), which nests Biseridens (Fig. 1, Li and Cheng 1997; Liu, Rubidge and Li 2009) far from anomodonts, between Archaeosyoson and Jonkeria and kin among the Tapinocephalia.

Figure 1. Biseridens and Phthinosuchus, two related therapsids that have been giving paleontologists fits.

Phthinosuchus, according to Wikipedia
“is the sole member of the the family Phthinosuchidae. It may have been one of the most primitive therapsids.” Not so, according to the large reptile tree (Fig. 2) where Phthinosuchus (Fig. 1, Efremov 1954) nests between Eotitanosuchus and Archaeosyodon + Biseridens at the base of the Dinocephalia.

So traditional nestings seem to be a little behind the times.
According to Liu, Rubidge and Li 2009, “Synapomorphies that distinguish Biseridens as an anomodont and not an eotitanosuchian as previously described: short snout (1); dorsally elevated zygomatic arch (2) and septomaxilla lacking elongated posterodorsal process between nasal and maxilla (3). The presence of a differentiated tooth row (4); denticles on vomer, palatine and pterygoid (5); contact between tabular and opisthotic (6); lateral process of transverse flange of pterygoid free of posterior ramus and absence of mandibular foramen exclude it from other anomodonts (7). Cladistic analysis indicates Biseridens to be the most basal anomodont (8).

Well, according to the large reptile tree…

1. Eotitanosuchus has a long snout because it is basal to the clade of long snouted basal gorgonopsians and therocephalians. Biseridens ancestors, like Phthinosuchus, and Archaeosyodon, never had a long snout.
2. the zygomatic arch (squamosal principally) is not dorsally elevated in the fossil (Fig. 1)
3. sisters likewise lack this septomaxilla trait
4. the dual rows of post-canine teeth and the large orbit in Biseridens are autapomorphies that distinguish it from sisters
5. Denticlaes are also found on the palate of Phthinosuchus. I don’t have data for closer sisters.
6. I don’t have comparable occipital data here
7. I don’t have comparable palatal data here
8. Be careful when a taxon nests as the ‘most basal’ to any clade without many more basal taxa on the inclusion list. As in another purported basal synapsid taxon, Caseasauria, it turns out that Biseridens actually nests elsewhere (Fig. 2).

Learn more about basal anomodonts here.

Figure 2. Basal therapsid tree. Note the nestings of Phthinosuchus and Biseridens far from where tradition al paleontologists have been saying. I think more taxa near the base of the tree make tis tree distinct. Note the weak bootstrap scores at the nodes splitting Suminia from Venjukovia and splitting the basal dromasaurs.

 

References
Efremov IA 1954, The fauna of terrestrial vertebrates in the Permian copper sandstones of wester Cis-Urals: Travaux de I’institut Paleozoologique de l’Academie des Sciences de l’URSS, v. 54, 416pp.
Li J and Cheng Z 1997. First discovery of eotitanosuchian (Therapsida, Synapsida) of China. Vertebr. Palasiatica 35, 268–282.
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. online

wiki/Biseridens
wiki/Jonkeria
wiki/Phthinosuchus

 

Updated Therapsid Tree

No big news here…
Add a few taxa…Discover that a few taxa represented by old drawings (Nikkasaurus, Niaftasuchus) actually belong elsewhere… (just outside the Synapsida).

And the therapsid subset (59 taxa) of the large reptile tree (674 taxa) gets an update (Fig. 1) with better Bootstrap scores.

Figure 1. Basal therapsid tree, updated.

The topology remains basically the same. 
A few long-snouted basal theriodonts were added along with Phthinosuchus. The anomodonts still split off at the base of the Therapsida, following the appearance of the basal taxon, Cutleria. This tree remains distinct from predecessor trees in this basic topology, I think because more basal, pelycosaur-like, taxa are included here and not elsewhere.

There is still a lot of convergence here.
And this is probably the main reason why tree topologies don’t match.

1. Dicynodonts and dicynodont mimics (Tiarajudens, Anomocephalus).
2. Gorgonopsids and the gorgon-mimic Herpetoskylax (a basal burned).
3. Basal therapsids like Stenocybus and a basal therapsid-mimic, Microurania (Fig. 2).
4. Anteosaurs and the anteosaur-mimics Deuterosaurus, Estemmenosuchus and Ulemosuchus (Fig. 2).
5. And more convergence among the untested taxa within the therocephalians and cynodonts.

Figure 2. Click to enlarge. Basal therapsid tree based on phylogenetic analysis and presented with skulls

I dug back into this tree and gathered better data
because Bootstrap scores were not robust in the prior analysis. It was an amazing two-week journey. And when better data becomes available, more refinements will attempted. At this point, the gradual accumulation of traits in all derived taxa are apparent.