The Permian Period

Article by: J. D. Dixon
Edited by: Lewis Haller, Jack Wood, and Harry T. Jones

Two Dinogorgons, a genus of gorgonopsid, fighting over a meal. Gorgonopsids are therapsids, a type of derived synapsid. Artwork by Julius Csotonyi.

The Permian Period started 298.9 ± 0.15 million years ago (Ma) and ended 251.902 ± 0.024 Ma, and was the final period of the Paleozoic Era. During this period, Laurasia and Gondwana, the two minor supercontinents, merged to form the supercontinent Pangaea. The Central Pangaea  mountains spread in an east-west orientation, and the size of this landmass caused substantial consequences for global climate. Large expanses of desert occupied northern Pangaea, while large ice sheets covered the southern part of the continent. There was a major glaciation spanning around two million years during the period.

Glacial cycles caused dramatic sea level regression, exposing continental shelves and triggering catastrophic effects for marine invertebrates. Crinoid, brachiopod, and bryozoan communities were completely destroyed over a course of 10 million years. Yet some organisms thrived as a result of this. Bivalves became plentiful as they could occupy the vacant niches left behind by brachiopods, and ammonoid cephalopods flourished. In the oceans, vertebrates developed significantly. Ray-finned fish (actinopterygians) and cartilaginous fish (chondrichthyans) diversified, and in the Artinskian Age, the fearsome ratfish Helicoprion swam globally. Certain tetrapods, such as Mesosaurus, even readapted to life in the water, some 20 million years after the initial terrestrialisation of their ancestors.

Lystrosaurus curvatus,  a herbivorous therapsid. This was the only species of Lystrosaurus to survive the End-Permian Mass Extinction. Artwork by Jack Wood.

At the start of the period, terrestrial fauna was very similar to that of the Carboniferous, but during the Permian the tetrapods took on all new forms. This period saw the rise of advanced synapsids. Synapsids are split into two groups, the more basal pelycosaurs and the more derived therapsids. Evolving from the sprawling Carboniferous predators, the top hunters of the Permian had numerous new adaptations. Their teeth became heterodont, meaning they had differential teeth as opposed to the same dental morphology throughout the mouth. They had also developed a more erect gait, so that their legs were positioned underneath their body. Their eyes became more forward-facing, and their ears began to develop in a way similar to the structure of the modern mammalian ear. Some of the top predators included the pelycosaur Dimetrodon and the gorgonopsid Inostrancevia.

Herbivores also developed greatly throughout the Permian. They developed sizeable and dulled teeth capable of cropping vegetation, and thick ribs forming a barrel-shaped chest, which indicate a large digestive tract. Some of the strangest herbivores to date wandered the Earth at this time. Cotylorhynchus, a large pelycosaur, had the smallest skull relative to body size of any synapsid. An Early Permian herbivore called Tiarajudens even had sabre-canines, which may have been used in display, combat, or to ward off predators.

After the desolation of the Carboniferous rainforests, many other plant species began to thrive. Seed plants such as glossopterids and cycads appeared while conifers became more important. The Ginkgoales, an order of non-flowering plants, first appeared in the Permian and survives to this day.

The End-Permian Mass Extinction. Artwork by Julius Csotonyi.

The Permian ended with an event often regarded as the most severe recorded mass extinction of all time. Globally, this killed off ~ 85% of marine species and ~ 70% of terrestrial vertebrate genera. The trilobites, one of the most famous Paleozoic groups, were entirely wiped out. The event is thought to have been triggered by volcanism from the Siberian Traps – the largest known eruption of continental flood basalts – coinciding with the end of the Permian. The extinction is spread across two separate events. In the Capitanian (late Middle Permian) there was an increased extinction rate. Then, in the late Changhsingian (late Late Permian), there was a rapid pulse of extinction.

Image References
[1] Two Dinogorgons by Julius Csotonyi.
[2] Lystrosaurus curvatus by Jack Wood.
[3] The End-Permian Mass Extinction by Julius Csotonyi.

Information References and Further Sources
[1] Battail, B., and Surkov, M. V. (2003). ‘Mammal-like reptiles from Russia’, in Benton, M. J., Shishkin, M. A., Unwin, D. M., and Kurochkin, E. N. (revised ed.) The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press. pp. 86-119. Accessed 26th March 2020. Click Here.
[2] Bowring, S. A., Erwin, D. H., Jin, Y. G., Martin, M. W., Davidek, K., and Wang, W. (1998). ‘U/Pb Zircon Geochronology and Tempo of the End-Permian Mass Extinction’, Science, 280 (5366), pp. 1039-1045. Accessed 27th March 2020. Click Here.
[3] Chart drafted by K. M. Cohen, D. A. T. Harper, P. L. Gibbard, and J.-X. Fan (c) International Commission on Stratigraphy, March 2020. To cite: Cohen, K. M., Finney, S. C., Gibbard, P. L. & Fan, J.-X. (2013; updated). The ICS International Chronostratigraphic Chart. Episodes 36: 199-204. Accessed 25th October 2020. Click Here.
[4] Cisneros, J. C., Abdala, F., Rubidge, B. S., Dentzien-Dias, P. C., and de Oliveira Bueno, A. (2011). ‘Dental Occlusion in a 260-Million-Year-Old Therapsid with Saber Canines from the Permian of Brazil’, Science, 331 (6024), pp. 1603-1605. Accessed 26th March 2020. Click Here.
[5] Dorling Kindersley. (2009). ‘Permian’, in Prehistoric. Great Britain: Dorling Kindersley Limited. pp. 171-193.
[6] Fischer, T. C., Meller, B., Kustatscher, E., and Butzmann, R. (2010). ‘Permian ginkgophyte fossils from the Dolomites resemble extant O-ha-tsuki aberrant leaf-like fructifications of Ginkgo biloba L, BMC Evolutionary Biology, 10 (1), pp. 337. Accessed 30th June 2020. Click Here.
[7] Hampe, O., Hairapetian, V., Dorka, M., Witzmann, F., Akbari, A. M., and Korn, D. (2013). ‘A first Late Permian fish fauna from Baghuk Mountain (Neo-Tethyan shelf, central Iran)’, Bulletin of Geosciences, 88 (1), pp.1-20. Accessed 27th March 2020. Click Here.
[8] Knoll, A. H., Bambach, R. K., Payne, J. L., Pruss, S., Fischer, W. W. (2007). ‘Paleophysiology and end-Permian mass extinction’, Earth and Planetary Science Letters, 256 (3-4), pp. 295-313. Accessed 27th March 2020. Click Here.
[9] Stovall, J. W., Price, L. I., and Romer, A. S. (1966). ‘The Postcranial Skeleton of the Giant Permian Pelycosaur Cotylorhynchus romeri’, Museum of Comparative Zoology, Harvard University, 135 (1). Accessed 26th March 2020. Click Here.