Lobalopex: Finally another therapsid enters the TST!

It’s been awhile
since the last therapsid was traced and scored. Today two taxa enter the TST.

Figure 1. Cladogram of ten taxa employed by Sidor et al. 2004.

Figure 1. Cladogram of ten taxa employed by Sidor et al. 2004.

Sidor, Hopson and Keyser 2004
introduced a new ‘biarmosuchian’ and ‘burnetiamorph” therapsid from the Permian of South Africa. They named their new find Lobalopex mordax (CGP/1/61, Fig. 2, skull length 15cm). They reported, “a cladistic analysis including ten biarmosuchian taxa indicates that Lobalopex is the sister taxon to Burnetiidae and that Lemurosaurus is the most primitive burnetiamorph.” (Fig. 1).

After testing
in the Therapsid Skull Tree (= TST, 73 taxa, Fig. 3) Lobalopex nested  as a member of the Burnetia clade, matching the nesting of Sidor, Hopsona and Keyser 2004.

Figure 1. Lobalopex added to previous nested burnetiidae.

Figure 2. Lobalopex added to previous nested burnetiidae. It has a longer skull than others in this clade. Look to Herpetoskylax to imagine an uncrushed Lobalopex skull.

Sidor et al.
note the dorsal skull is crushed (it looks melted!) dorsoventrally. The rest of the skull is not crushed. Photos of the original material have not been published. Look to Herpetoskylax (Fig. 2) to imagine an uncrushed Lobalopex skull (Fig. 2).

A tiny horn boss
is present on the rostrum of Lobalopex. That horn boss gets bigger in Proburnetia and Burnetia (Fig. 2), but skips Lemurosaurus. The ventral portion of the Lobalopex retroarticular process wa lost during collection. The supratemporals (bright green) are fused to underlying bones. Lobalpex has a longer rostrum, relative to orbit length, than others in its clade, convergent with Eotitanosuchus.

Strangely,
little to no post-cranial material is known from this clade. Was it an herbivore or carnivore?

Figure 3. TST with the addition of Lobalopex nesting in the Burnetia clade.

Figure 3. TST with the addition of Lobalopex nesting in the Burnetia clade.

Lobalopex is derived from Lemurosaurus
in Sidor, Hopson and Keyser (Fig. 1), but the other way around in the TST (Fig. 3). Ictidorhinus (Fig. 2) is the outgroup in both cladograms. Herpetoskylax was not mentioned by Sidor, Hopson and Keyser 2004 because it was published later, not until 2006.

Figure 4. More recent cladograms that include Herpetoskylax and Lobalopex.

Figure 4. More recent cladograms that include Herpetoskylax and Lobalopex.

More recent cladograms 
that include Herpetoskylax and Lobalopex (Kruger et al. 2015, Kammerer 2016; Fig. 4) presume Biarmosuchus is the outgroup taxon. By contrast in the TST (Fig. 3) Biarmosuchus is the outgroup to more derived therapsid taxa, as is Rubidgina (Fig.5), which also enters the TST (Fig. 3) today, nesting basal to gorgonopsids and therocephalians + cynodonts + mammals.

Figure 5. Rubidgina skull in 4 views. Note the wide cheeks rotating the orbits anteriorly.

Figure 5. Rubidgina skull in 4 views. Note the wide cheeks rotating the orbits anteriorly. This taxon is not basal to the Burnetia clade in the TST.

With Rubidgina added to the deep time lineage of humans
it would not be too far off the mark to say, the deep time ancestors of Little Red Riding Hood once looked quite a bit like the big bad wolf. How ironic. ‘Grandma’ really did have such big teeth!


References
Sidor CA, Hopson JA and Keyser AW 2004. A new burnetiamorph therapsid from the Teekloof Formation, Permian, of South Africa. Journal of Vertebrate Paleontology 24(4):938–950.

wiki/Lobalopex

Styracocephalus x2 enters the TST

Fraser-King et al. 2019
bring us new data on Styracocephalus (Fig. 3), a purported dinocephalian therapsid from Late Permian South Africa. Unfortunately the Fraser-King et al. phylogenetic analysis (Fig. 1) excludes relevant taxa (like Phthinosuchus) and includes one unrelated taxon, Tetraceratops. The authority for this criticism is a larger study, the therapsid skull tree (TST, 72 taxa, subset Fig. 2) a side branch of the large reptile tree (LRT, 1579 taxa). It includes the relevant taxa in the Fraser-King et al. study, and many more excluded from Fraser-King et al.

Figure 1. Cladogram from Fraser-King et al. 2019. Compare to figure 2 where many more taxa are included.

Figure 1. Cladogram from Fraser-King et al. 2019. Compare to figure 2 where many more taxa are included. Tetraceratops is not related to any therapsid, but nests closer to Limnoscelis.

FIgure 2. TST with the addition of two specimens attributed to Styracocephalus and Raranimus. Compare to fewer taxa in figure 1.

FIgure 2. TST with the addition of two specimens attributed to Styracocephalus and Raranimus. Compare to fewer taxa in figure 1. Here Styracocephalus is not related to tapinocephalids. The TST is fully resolved.

Both the holotype of Styracocephalus
and the new referred specimen nest together in the LRT despite their many morphological differences (Fig. 3). Even so, I think the differences are strong enough to erect a new genus for the new specimen. The two nest with the Phthinosuchus clade in the LRT, a taxon not included in the Fraser-King et al. study.

Figure 1. At left, the holotype of Sclerocephalus SAM PK 8936. At right the distinctly different referred specimen to scale BPI I 7141.

Figure 3. At left, the holotype of Sclerocephalus SAM PK 8936. At right the distinctly different referred specimen to scale BPI I 7141.

So, in this case,
I’m a splitter, not a lumper. And I wish Fraser-King et al. had included a few more taxa.

PS
Raranimus also entered the TST because Fraser-King included that taxon. Raranimus nested with Ictidorhinus, and ironically, could be congeneric given how little is known of Raranimus.


References
Fraser-King S, Benoit J, Day MO and Rubidge BS 2019. Cranial morphology and phylogenetic relationship of the enigmatic dinocephalian Styracocephalus platyrhynchus from the Karoo Supergroup, South Africa. Palaeontologia africana 54: 14–29.

 

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.

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.

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.

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.

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.


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

SVP 2018: Hipposaurus unprepared verts finally described with µCT scans

In the large reptile tree (LRT, 1306 taxa) Hipposaurus (Fig. 1; Haughton 1929, skull length 21cm, length 1.2m) nests at the base of the carnivorous therapsids, not far from finless pelycosaurs, like Haptodus and basal amonodonts like Stenocybus. For all that time the vertebral column has remained buried and unstudied.

Figure 2. The skull of Hpposaurus was larger than that of its sisters and predecessors among the basal Therapsida.

Figure 1. The skull of Hpposaurus was larger than that of its sisters and predecessors among the basal Therapsida.

We looked at Hipposaurus
earlier as a more likely trackmaker for Dimetropus ichnites.

Peecock et al. 2018
describe µCT scans of the previously undescribed vertebral column of Hipposaurus. With this data  they propose new relationships with other hipposaurids known only from vertebrae.

FIgure 3. Hipposaurus compared Dimetropus. The overall and leg length is right, as are many of the digits. Unfortunately the medial digits are too short in Hipposaurus. Hipposaurus has a narrower gauge and lifted its belly of the ground, as did the Dimetropus trackmaker.

FIgure 2. Hipposaurus compared Dimetropus. The overall and leg length is right, as are many of the digits. Unfortunately the medial digits are too short in Hipposaurus. Hipposaurus has a narrower gauge and lifted its belly of the ground, as did the Dimetropus trackmaker.

The Peecock team concludes with caution,
“Phylogenetic analysis underscores the startling homoplasy between biarmosuchians and
archosauromorphs: when biarmosuchian vertebrae are coded into an archosauromorph data matrix, they form a monophyletic clade within Avemetatarsalia. Extreme caution is needed when interpreting Permian vertebrae as archosauromorphs.”

As we’ve seen before,
convergence is rampant in the LRT.

References
Boonstra LD 1952. Die Gorgonospier-geslag Hipposaurus en die familie Ictidorhinidae: Tydskr. Wet. Kuns 12:142-149.
|Haughton SH 1929.
 On some new therapsid genera: Annals of the South African Museum 28(1):55-78.
Peecock et al. (5 co-authors) 2018. Vertebral osteology of Hipposaurus boonstrai (Therapsida, Biarmosuchia) from the Middle Permian of South Africa, with implications for the evolution of Archosauromorpha. SVP abstracts.

 

wiki/Hipposaurus

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.

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 1. 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!

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 2. The skull of Hpposaurus was larger than that of its sisters and predecessors among the basal Therapsida.

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.

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 ArchaeosyodonBiseridens 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 3. Basal therapsid tree.

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 3. Basal therapsid tree.

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

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.

Tetraceratops news

Updated Jan 10, 2020
with better data on Tetraceratops in Spindler 2020.

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

A paper by Spindler (2014) sought the oldest therapsid…
and found no reason to nest the former best candidate, Tetraceratops (Fig. 1), with basal therapsids, confirming what was reported here in 2011.

Figure 5. Tetraceratops tracing using DGS and freehand illustration by Spindler 2020.

Figure 5. Tetraceratops tracing using DGS and freehand illustration by Spindler 2020.

From the abstract: “Since the successful clade of therapsids occurs rather suddenly in the fossil record of Guadalupian age*, the reconstruction of their origin is questionable and based on little data. Concerning the Artinskian taxon Tetraceratops insignis**, broadly accepted as the oldest and basal-most member, no close relation to therapsids could be found during the re-documentation. Instead, a fragmentarily preserved vertebral sequence from the Desmoinesian assemblage [Late Pennsylvanian, Westphalian D] of Florence, Nova Scotia, is considered to be a new candidate for the oldest therapsid. This pushes back their origin farther than required by phylogenetic results. Moreover, it supports the ghost lineage of unknown Carboniferous and Early Permian therapsids.”

* The large reptile tree nests the basalmost therapsid, Cutlieria, in the Early Permian.
** The large reptile tree nests Tetraceratops (Early Permian) with the limnoscelid, Tseajaia.

Spindler reports, “The problems when evaluating Tetraceratops are (1) its highly autapomorphic character combination, such as ornamentation, short facial region, and specialized dentition, and (2) the poor preservation of the single holotypic skull. The specimen has been re-studied carefully and is currently under re-evaluation. Anatomical identifications take into account a high degree of compaction, but although a simple mode of deformation. In contrast to previous workers, the therapsid synapomorphies could not be reproduced, resulting in a haptodont-grade classification*** independent from the same result by CONRAD & SIDOR (2001) and supported by LIU et al.(2009).”

*** Spindler did not consider a larger taxon list that included Saurorictus and limnoscelids.

Unfortunately
I cannot nest a vertebral sequence in the large reptile tree, so until I can (probably never), I accept Spindler’s observations and interpretations.

References
Spindler F 2014. Reviewing the question of the oldest therapsid. Paläontologie, Stratigraphie, Fazies (22) Freiberger Forschungshefte C 548: 1–7.

Nikkasaurus postcranial: how to work with crappy data

Updated May 10, 2016 with a new nesting of Nikksaurus with basal prodiapsids.

It’s hard to find data on Nikkasaurus,
a tiny basal prodiapsid without fangs. The only data I know comes from Ivahnenko (2000) in the form of a drawing or two (Fig. 1). Earlier we looked at just the skull of Nikkasaurus and how tiny it was, now nesting with Mycterosaurus at the base of the Prodiapsida.

Figure 1. Nikkasaurus and what little is known of its postcrania. Above, in situ. Below, tentative reconstruction. If anyone has a picture of the fossil itself, please send it.

Figure 1. Nikkasaurus and what little is known of its postcrania. Above, in situ. Below, tentative reconstruction. If anyone has a picture of the fossil itself, please send it.

The longer legs
that made prodiapsids special are seen here. No doubt this is a product of paedomorphy as the only other basal synapsid/diapsid juvenile I know of, baby Dimetrodon, also had longer legs than its adult counterpart. The difference here: the crus and antebrachium don’t appear to be very bowed between the tibia and fibula, as in the closest sister, Mycterosaurus.

Some basal prodiapsids
lose the primitive fang. Nikkasaurus is one of those.

References
Ivahnenko MF 2000. Cranial morphology and evolution of Permian Dinomorpha (Eotherapsida) of eastern Europe. Paleontological Journal 42(9):859-995. DOI: 10.1134/S0031030108090013

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.