Kingdoms of Life > 
Animalia > Vertebrata > Tetrapoda > Theropsida > Therapsida Palaeos website (to which many links on these pages point to anyway. More info hereDear 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.
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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Print 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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Permian Period
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Therapsida | Theriodontia | Gorgonopsia |
Palaeos Page (incorporates some of this material, plus a lot of additional material)
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