Karoo reveals mass extinction around 260 million years ago
This is an illustration of the Guadalupian extinction. Credit: Wits University
An international team led by researchers from the Evolutionary Studies
Institute (ESI) at the University of the Witwatersrand, Johannesburg,
has obtained an age from rocks of the Great Karoo that shed light on the
timing of a mass extinction event that occurred around 260 million
This led to the disappearance of a diverse group of early mammal-like
reptiles called dinocephalians, which were the largest land-living
animals of the time.
The project was led by Dr Michael Day, a postdoctoral fellow at Wits
University, and the findings are contained in paper, titled: When and
how did the terrestrial mid-Permian mass extinction occur? Evidence from
the tetrapod record of the Karoo Basin, South Africa, published today, 8
July 2015, in the latest issue of the Royal Society's biological
journal, Proceedings of the Royal Society B.
The Karoo is very rich in fossils of terrestrial animals from the
Permian and Triassic geological periods, which makes it one of the few
places to study extinction events on land during this time. As a result
South Africa's Karoo region provides not only a historical record of
biological change over a period of Earth's history but also a means to
test theories of evolutionary processes over long stretches of time.
By collecting fossils in the Eastern, Western and Northern Cape
Provinces the team was able to show that around 74-80% of species became
extinct along with the dinocephalians in a geologically short period of
The new date was obtained by high precision analyses of the relative
abundance of uranium and lead in small zircon crystals from a volcanic
ash layer close to this extinction horizon in the Karoo.
This provides a means of linking the South African fossil record with
the fossil record in the rest of the world. In particular, it helps
correlate the Karoo with the global marine record, which also records an
extinction event around 260 million years ago.
"A mid-Permian extinction event on land has been known for some time but
was suspected to have occurred earlier than those in the marine realm.
The new date suggests that one event may have affected marine and
terrestrial environments at the same time, which could mean its impact
was greater than we thought," says Day.
The mid-Permian extinction occurred near the end of what geologists call
the Guadalupian epoch that extended from 272.3 to around 259.1 million
years ago. It pre-dated the massive and much more famous end-Permian
mass extinction event by 8 million years.
"The South African Karoo rocks host the richest record of middle Permian
land-living vertebrate animals. This dataset, the culmination of 30
years of fossil collecting and diligent stratigraphic recording of the
information, for the first time provides robust fossil and radioisotopic
data to support the occurrence of this extinction event on land," says
"The exact age of the marine extinctions remains uncertain," says
Jahandar Ramezani of Massachusetts Institute of Technology and who was
responsible for dating the rocks, "but this new date from terrestrial
deposits of the Karoo, supported by palaeontological evidence,
represents an important step towards a better understanding of the
mid-Permian extinction and its effect on terrestrial faunas."
Michael O. Day, Jahandar Ramezani, Samuel A. Bowring, Peter M. Sadler,
Douglas H. Erwin, Fernando Abdala, Bruce S. Rubidge. 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 DOI: 10.1098/rspb.2015.0834