Under this heading are two very poorly known basal therapsids from the Middle Permian of Russia that do not seem to be closely related, but in any case are placed (rightly or wrongly) each in their own family. The group "Phthinosuchia" is a hodgepodge of a very fragmentary cranium (Phthinosuchus), a wastebasket full of dentary fragments, and a few postcrania of which there is no guarantee they belong to the same animal. All that can be said is that this crappy material comes for the most part from animals close to the Therapsid stem, and which may or may not be related to the Biarmosuchia. It is not likely that these remains do represent valid therapsid lineages, but a lot more material is required if light is to to be shed on the early rich evolutionary radiation of teh Middle Permian therapsids. In teh meantime, the following data analysis is very tentatively offered.
Ecological niche: medium-sized terrestrial carnivores
Time: middle Permian
Distribution: although so far fossil remains are known only from eastern Russia it is likely these animals had a much wider, probably worldwide ( Pangea) distribution
preferred food: smaller tetrapods
length: around 1.5 meters
weight: around 15 to 30 kg
Metabolism: partially endothermic???
Predators: Eotitanosuchids and Brithopodids
Ancestor: Basal Therapsid (Tetraceratops-like ancestor?)
Replaced: Medium-sized Sphenacodontid, and Varanopseid pelycsaurs
Replaced by: Theriodonts
Descendents: none - but for earlier (hypothetical pre-Wordian age) forms maybe Brithopodids, Bairmosuchidae or Eotitanosuchidae????
Taxonomic status - two monospecifc families - almost certainly an artificial grouping of very poorly known basal therapsids
Only a single partial skull is known for this family, of which the front part of the snout is lacking. On the right side mostly only the imprint of bones remains. Overall it is insufficiently prepared and locally hidden by plaster. It is strikingly similar to that of a sphenacodont, but with larger synapsid openings behind the eyes and more prominent canine teeth. It would seem to be intermediate in structure between the pelycosaurs and the therapsids. No postcranial elements have been attributed to this family. The anterior part of the skull illustrated by Seeley has since been lost. The frequent reproductions of Efremov's reconstruction gives the impression that the skull is a lot more complete than it really is. The images shown here give a more correct representative than that in many text books. The painting at teh top of the page, while quite possibly representative of what an ancestral Therapsid (intermediate, say, between Tetraceratops and Biarmosuchus) may have looked like, can not be taken as a factual recobnstruction of this species.
This skull has been described in great detail by Tataranov (1974). Even though it is compressed laterally it must have been high and narrow, with a convex dorsal profile and a temporal fossa that is higher than wide. The skull roof is relatively narrow at the level of the large orbits and wide at the level of the temporal fossae. The postorbital and temporal arches are thin; the occiput is high and slightly inclined ventro-anteriorly; there exists a large number of postcanines. The mandible is slender, and the dentary does not seem to extend dorsally beyond the level of the subangular.
Phthinosuchus Efremov 1954(=Rhopalodon pp. Seeley 1894, Watson 1921 and 1942, Nopsca 1928)
Emended diagnosis: Snout high and short? Area of the temporal fossa nearly equal to that of the orbit, but high and narrow. Interorbital roof much smaller than intertemporal roof. Short lacrymal. Frontal participates largely in the orbit. Pineal protuberance accentuated and situated near the posterior limit of the cranial roof. Occiput wide and high. Mandible slender.
Relationships: This specimen has been described at length a number of times, e.g. by the Russian Palaeontologists Efremov in 1954 and Tatarinov in 1974. It was said to be related to the Brithopodidae or Carnivorous Dinocephalians by earlier researchers like Seeley and Watson. Nopcsa in 1928 classified it in the gorgonopsians, and was followed in this by Efremov and by Romer. But no Gorgonopsian specializations are not found, apart from some shared primitive characteristics. Romer, noting the absence of gorgonopsian specializations, and used Phthinosuchus to erect the infraorder "Phthinosuchia", a taxon similiar to the "Eotheriodonta" of Olson and Chudinov. Although Robert Carroll includes the suborder "Phthinosuchia" in his genus list, and the term "Eotheriodonta" is still used by Russian paleontologists, these supra-familial taxa are almost certainly invalid.
Other Phthinosuchus characters indicate less Gorgonopsid and more Brithopodid relationships. The proportions of the skull roof are also Brithopodid. However other brithopodid specializations are not found, such as the intertemporal narrowness already present in its contemporary Archaeosyodon. There is a median suture on the underside (ventral), rather like in Eotitanosuchus. But in all respects, in view of the incomplete state of the specimen and absence of the posteranial skeleton, it appears impossible to have any precise idea in regard to its affinities.
Diagnosis: Elongate lower jaw, with upright symphysis but without a marked chin. High position of the mandibular articulation. Rudimentary coronoid process. Elongate angular with reflected lamina extending to the posterior limit of the jaw. Mandibular fossa opening exteriorly.
There is only one genus, Phthinosaurus , and one species, known from an incomplete lower jaw (illustrated here). Two dentary fragments, a scapula, ulna, and angular, from the same locality have also been referred to this species, so that all that is known of it is just these few scraps of bone (don't you just love Palaeontology?). This specimen was found among the Belebei-Mezen Cotylosaur Complex, in association with Labyrinthodont amphibians, Anapsid reptiles, and the abarrent lizard-like Pelycosaur Mesenosaurus.
This is an even more fragmentary specimen than Phthinosuchus. It does not appear to be closely related to that genus, and was placed in its own family. The principal difference between this lower jaw and that of the Phthinosuchus resides in the higher position of the articulation and the beginning of a coronoid process on the dentary. Thus a mixture of sphenacodont and theriodont (therocephalian) characters is found. In any case, this specimen is so incomplete that beyond basal therapsid relationships nothing can really be said of it. It may turn out to belong to one of the other early Therapsid families.
|some Links and References|
Denise Sigogneau-Russell, "Theriodontia I - Phthinosuchia, Biarmosuchia, Eotitanosuchia, Gorgonopsia" Part 17 B I, Encyclopedia of Paleoherpetology, Gutsav Fischer Verlag, Stuttgart and New York, 1989
Everett C. Olson, "Late Permian Terrestrial Vertebrates, USA and USSR", Transactions of the American Philosophical Society, Philadelphia, vol 52 part 2, 1962
Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals, ed. Barry Cox et al.
Edwin H. Colbert, Evolution of the Vertebrates, 2nd edition, 1969, John Wiley & Sons
note by Christian Kammerer (scroll down) - states the term "Phthinosuchidae" (=Phthinosuchia) is invalid
Palaeos Page (incorporates some of this material, plus a lot of additional material)