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Evolutionary Relationships of the Gorgonopsia

Hi Christian
Do you think the Gorgonopsids belong to the same clade as the higher theriodonts (Therocephalia and Cynodontia)?  Boonstra once made the interesting suggestion that they belong to the Dinocephalian group, but someone else (I cant remember who) refuted this saying that the Gorgons shared only primitive characters with the Dinocephalians.
best regards
Alan

Dear Alan,

In regards to you inquiries about the Gorgonopsia (more properly spelled Gorgonopia, actually, but old habits die hard), they are rather clearly not dinocephalians. Any of the older sources (Broom, Boonstra, Romer) on therapsid phylogeny are highly inaccurate and therapsid research has progressed by leaps and bounds since this time. Some really great reviews of current therapsid phylogeny include Hopson & Barghusen, 1986, Hopson, 1991, and Kemp, 1988.  I personally consider the gorgonopsians to form a well-supported clade with the therocephalians and cynodonts called the Theridontia (the cynodonts and therocephalians almost certainly form a clade, the Eutheriodontia). That the gorgonopsians are closer to the eutheriodonts than the dinocephalians is practically unquestioned, especially since many taxa previously considered to be "primitive gorgonopsians" based solely on plesiomorphies [shared primitive characteristics] are now excluded from the group and instead make up the probably paraphyletic taxon of basalmost (primitive ancestral) therapsids---the "Biarmosuchia". Classic "protogorgons" now included in the biarmosuchians are Biarmosuchus itself, the Karoo ictidorhinids and hipposaurids, and the aberrant burnetiids (the wonderful and fascinating taxon Styracocephalus platyrhynchus, once grouped with the burnetiids solely on the basis of strange skull ornamentation, has been put firmly into the Dinocephalia in van den Heever & Rubidge's 1997 paper in Lethaia). There remains one question, however, that greatly influences placement of the gorgonopsians, and that is the anomodontia. It is now recognized (based on a slew of new basalmost anomodonts (the traditional "dromasaurs" and "venyukoviamorphs"--two para/polyphyletic groups) from Russia and the Karoo) that the Anomodontia has no relation to the Dinocephalia as was once thought, and in most analyses is regarded as part of an unresolved trichotomy with Dinocephalia and Theriodontia. However, some workers (I think Kemp and maybe Battail--I'll have to check on that one) have suggested that anomodonts are more derived than Gorgonopsians and form the outgroup to Eutheriodontia, with Gorgonopsia as the sister group to this anomodont+eutheridont clade. However, though it does seem to appear that anomodonts are closer to theriodonts than the dinocephalians, I strongly doubt that they are more closely related to eutheriodonts than gorgonopsians. Most of the features used to distance gorgonopsians from the eutheriodonts are plesiomorphies that would be found in the ancestors of any of the three eutherapsid (eutherapsida consisting of the three major therapsid groups dinocephs, anomdonts, and theriodonts), and I'm just not convinced. Besides, cladistic analyses using many of the traditional features assigned to the gorgonopsians support theriodont monophyly.


Sincerely,
Christian Kammerer

This fact was brought up extremely recently by Greek and Latin scholars with an interest in prehistoric animals. Actually, it started because some people pointed out that the very-well known dinosaur groups Ceratopsia and Ceratopsidae were improperly formed from the ancient languages and are more correctly spelled Ceratopia and Ceratopidae based on the rules of nomenclature. Then, a few people noticed this and said "Hey, this applies to the Gorgonopsia and Gorgonopidae too". Of course, Ceratopsia is one of the best-known and established names in all of paleontology, so scientists are loath to start calling it "Ceratopia", and some think that in this case the incorrect form should be retained for reasons of clarity. The same could be argued for the Gorgonop[s]ia, but as a lesser-known group (therapsids always get short shrift compared to dinosaurs) the case is less strong. Hence Gorgonopia and Gorgonopidae have started to be used (see for example Tartarinov, 1999), but I still have trouble not saying "Gorgonopsia".
C.K.


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some printed references Print References some printed references

Hopson, J.A. 1991. "Systematics of the Nonmammalian Synapsida and Implications for Patterns of Evolution in the Synapsids." in Schultze, HP and Linda Trueb (eds.) Origins of the Higher Groups of Tetrapods. Comstock Publishing Associates. pp 635-693.

Hopson, J.A. and H. Barghusen. 1986. "An analysis of therapsid relationships." pp. 83-106 in Hotton, N., III, P.D. MacLean, J. Roth, and E. Roth (eds.). The Ecology and Biology of Mammal-like Reptiles. Washington: Smithsonian Institution Press.

For an alternative opinion (feature the "theriodont" dicynodont theory) see:

Rowe, T. 1988. "Definition, diagnosis, and origins of Mammalia." Journal of Vertebrate Paleontology. 8:241-264.


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page by M.Alan Kazlev, original material © Christian Kammerer
page created 10 November 1999. Reposted and last modified 1 September 2005, links updated 16 January 2010