Therapsida

Belongs within: Sphenacodontidae.
Contains: Eutherapsida.

The Therapsida are a clade including all synapsids except for the basal ‘pelycosaurs’, first known from the Middle Permian. Basal members of the clade include the Biarmosuchia, a group of small to medium-sized carnivores known from the Middle and Upper Permian of South Africa and Russia, characterised by the possession of uniformly small upper incisor teeth (Sidor 2003).

Synapomorphies (from Kemp 1988): Lateral temporal fenestra enlarged; supratemporal lost; shallow groove (external auditory meatus) on posterior face of squamosal; septomaxilla with long posterodorsal process; pineal foramen on raised boss; reflected lamina of angular greatly enlarged as thin sheet; jaw articulation shifted forwards; mobile basipterygoid articulation absent; interpterygoid vacuity reduced; palatal teeth reduced; paroccipital process extending more laterally than ventrally; vomer transversely widened between internal nares; transverse process of pterygoid shifted forward; no ossified intercentra in trunk; ossified sternum; cleithrum reduced, scapular blade narrow, coracoid and procoracoid reduced, screw-shaped glenoid absent; ilium expanded both anteriorly and posteriorly, acetabulum circular, fourth trochanter of femur absent; phalanges reduced.

<==Therapsida [Eotheriodontia]
    |--+--EutherapsidaS03
    |  `--Eotitanosuchus [Eotitanosuchia, Eotitanosuchidae]CL97
    |       `--E. olsoni Tchudinov 1960B93
    `--BiarmosuchiaS03
         |--BiarmosuchidaeTT05
         |    |--Biarmosuchoides romanovi Tverdochlebova & Ivakhnenko 1994TT05
         |    `--Biarmosuchus Chudinov 1960S03, D07 [incl. BiarmosaurusK88]
         |         |--B. antecessorD07
         |         |--B. tchudinoviD07
         |         `--B. tener Tchudinov 1960B93
         `--+--Hipposaurus Broom 1940S03, D07
            |    |--H. boonstrai Haughton 1929B93
            |    |--H. brinki Sigogneau 1970B93
            |    `--H. seelyiD07
            `--IctidorhinidaeS03
                 |  i. s.: Rubidgina angusticeps Broom 1942B93
                 |--Lycaenodon Broom 1925 [incl. Hipposauroides Boonstra 1952]S03
                 |    `--*L. longiceps Broom 1925 [incl. Hipposaurus rubidgei Broom 1940, *Hipposauroides rubidgei]S03
                 `--+--Ictidorhinus martinsi Broom 1913S03, B93
                    `--BurnetiamorphaS03
                         |--Lemurosaurus priceiS03
                         `--BurnetiidaeS03
                              |--Burnetia mirabilis Broom 1923B93
                              |--Proburnetia viatkensis Tatarinov 1968B93
                              `--BullacephalusS03
Therapsida incertae sedis:
  DelphinognathusN85
  Microurania [Microuraniidae]TT05
    `--M. minima Ivakhnenko 1995TT05
  Scylacosuchus [Scylacosauridae]TT05
    `--S. orenburgensisTT05
  Moschops Broom 1911D07
    |--M. capiensisD07
    |--M. koupensisD07
    |--M. oweniD07
    `--M. whaitsiD07
  Styracocephalus Houghton 1929D07
    `--S. platyrhynchusD07
  Tetraceratops Matthew 1908B93, D07
    `--T. insignis Matthew 1908B93
  PhthinosuchiaB93
    |--Knoxosaurus niteckii Olson 1962B93
    |--Steppesaurus gurleyi Olson & Beerbower 1953B93
    `--PhthinosuchidaeB93
         |--Phthinosaurus borissiaki Efremov 1940B93
         `--Phthinosuchus Efremov 1954D07
              |--P. discors Efremov 1954B93
              `--P. horissiakiD07

*Type species of generic name indicated

References

[B93] Benton, M. J. 1993. Reptilia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 681–715. Chapman & Hall: London.

[CL97] Cheng Z. & 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.

[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.

[K88] Kemp, T. S. 1988. Interrelationships of the Synapsida. In: Benton, M. J. (ed.) The Phylogeny and Classification of the Tetrapods vol. 2. Mammals pp. 1–22. Clarendon Press: Oxford.

[N85] Norman, D. 1985 (reprinted 2000). The Illustrated Encyclopedia of Dinosaurs. Salamander Books: London.

[S03] Sidor, C. A. 2003. The naris and palate of Lycaenodon longiceps (Therapsida: Biarmosuchia), with comments on their early evolution in the Therapsida. Journal of Paleontology 77 (5): 977–984.

[TT05] Tverdokhlebov, V. P., G. I. Tverdokhlebova, A. V. Minikh, M. V. Surkov & M. J. Benton. 2005. Upper Permian vertebrates and their sedimentological context in the South Urals, Russia. Earth-Science Reviews 69: 27–77.