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Mid-Permian mass extinction in Karoo Basin + Permian trackmakers

Ben Creisler

New papers:

Michael O. Day, Jahandar Ramezani, Samuel A. Bowring, Peter M. Sadler,
Douglas H. Erwin, Fernando Abdala & Bruce S. Rubidge (2015)
When and how did the terrestrial mid-Permian mass extinction occur?
Evidence from the tetrapod record of the Karoo Basin, South Africa.
Proceedings of the Royal Society B 2015 282 20150834
DOI: 10.1098/rspb.2015.0834

A mid-Permian (Guadalupian epoch) extinction event at approximately
260 Ma has been mooted for two decades. This is based primarily on
invertebrate biostratigraphy of Guadalupian–Lopingian marine carbonate
platforms in southern China, which are temporally constrained by
correlation to the associated Emeishan Large Igneous Province (LIP).
Despite attempts to identify a similar biodiversity crisis in the
terrestrial realm, the low resolution of mid-Permian tetrapod
biostratigraphy and a lack of robust geochronological constraints have
until now hampered both the correlation and quantification of
terrestrial extinctions. Here we present an extensive compilation of
tetrapod-stratigraphic data analysed by the constrained optimization
(CONOP) algorithm that reveals a significant extinction event among
tetrapods within the lower Beaufort Group of the Karoo Basin, South
Africa, in the latest Capitanian. Our fossil dataset reveals a 74–80%
loss of generic richness between the upper Tapinocephalus Assemblage
Zone (AZ) and the mid-Pristerognathus AZ that is temporally
constrained by a U–Pb zircon date (CA-TIMS method) of 260.259 ± 0.081
Ma from a tuff near the top of the Tapinocephalus AZ. This strengthens
the biochronology of the Permian Beaufort Group and supports the
existence of a mid-Permian mass extinction event on land near the end
of the Guadalupian. Our results permit a temporal association between
the extinction of dinocephalian therapsids and the LIP volcanism at
Emeishan, as well as the marine end-Guadalupian extinctions.




Marco Romano, Paolo Citton and Umberto Nicosia (2015)
Corroborating trackmaker identification through footprint functional
analysis: the case study of Ichniotherium and Dimetropus.
Lethaia (advance online publication)
DOI: 10.1111/let.12136

A study carried out on some excellently preserved footprints has
revealed the vital importance of functionality analysis, together with
morphological analyses, in settling systematics and attribution issues
in ichnological studies. To test the alleged reliability of
functionality studies in tetrapod ichnology, a careful analysis of
numerous specimens (both trackways and isolated footprints) of the
Gotha collection, referred to the Permian ichnotaxa Ichniotherium and
Dimetropus, has been carried out. The method, in addition to the
classical ichnological protocol, includes a careful and basic analysis
of the differential depth of the impression to evaluate biomechanics
and functional potentiality of the putative trackmaker in the light of
osteological structures. The analysis has led to the recognition of
two well-separated particular functionalities (over a complete
locomotion cycle), sharply distinguishable in Ichniotherium and
Dimetropus. The Ichniotherium trackmaker presents a functional axis in
the fore and hind limbs moved always along the medial side during the
stroke progression; in Dimetropus trackmaker there are at least two
functional axes, the first moved laterally in the initial stroke phase
and the second moved medially during the maximum load phase. Those
different functionalities are intimately linked to the particular
osteological characters present in diadectids and non-therapsid
synapsids. Thus, functionality analysis in the ichnological practice
is a valuable tool strongly recommended for use whenever possible.