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Theriognathus (Therapsida, Late Permian, South Africa) revised

Ben Creisler

A new paper:

Adam K. Huttenlocker and Fernando Abdala (2016)
Revision of the first therocephalian, Theriognathus Owen (Therapsida:
Whaitsiidae), and implications for cranial ontogeny and allometry in
nonmammaliaform eutheriodonts.
Journal of Paleontology (advance online publication)
DOI: http://dx.doi.org/10.1017/jpa.2015.32

Historically, the whaitsiid therocephalian Theriognathus Owen was one
of the earliest described nonmammalian therapsids, its morphology
helping to link phylogenetically the Paleozoic synapsids of North
America and southern Africa to their mammalian successors. However,
decades of taxonomic over-splitting and superficial descriptions
obscured the morphologic diversity of the genus, hindering its utility
as a study system for the evolution of synapsid cranial function as
well as its biostratigraphic significance in the Late Permian of
southern Africa. Here, we revise the status and provenance of all the
known specimens of Theriognathus from South Africa, Tanzania, and
Zambia. We present both qualitative and quantitative support for the
presence of a single morphospecies as proposed by some authors.
Proportional differences in skulls that were previously ascribed to
different morphotypes (‘Aneugomphius,’ ‘Notosollasia,’
‘Moschorhynchus,’ and ‘Whaitsia’) are largely size-related and
allometric trends are considered here in the context of jaw function
and prey prehension. Our results suggest that the single species,
Theriognathus microps, represented one of the most abundant Late
Permian therocephalians in southern Africa and is consequently a
potentially useful biostratigraphic marker for the upper
Cistecephalus-lower Dicynodon Assemblage Zone transition (i.e., late
Wuchiapingian). The wide range of preserved sizes in conjunction with
recent paleohistological evidence supports that individuals spent much
of their lives in an actively-growing, subadult phase. Later Dicynodon
Assemblage Zone records (e.g., upper Balfour Formation) are
unconfirmed as the genus was likely replaced by other theriodont
predators (e.g., Moschorhinus) leading up to the Permo-Triassic
boundary in the Karoo Basin of South Africa.