Literature Review: Permian and Triassic

by Carl Strang

The Permian Period that ended the Paleozoic Era, and the Triassic Period that began the Mesozoic Era, continue to attract researchers’ attention. This was a time of dramatic geological activity as the continents ground together to form the supercontinent of Pangaea, a time of two mass extinctions, and a time when the first dinosaurs evolved. Today I share notes from some of last year’s literature on this time period.

Part of a mural depicting a prosauropod (sauropodomorph), one of the early dinosaurs. Field Museum of Natural History exhibit.

Stephen E. Grasby, Hamed Sanei, Benoit Beauchamp. Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction. Nature Geoscience, 2011; DOI: 10.1038/ngeo1069     Deposits of coal ash in Canada support the view that the Siberian traps volcanic eruption involved coal beds, burning huge volumes of coal and releasing significant greenhouse gases while the toxic ash itself may have been a significant ocean contaminant. The consensus now is that this massive eruption, probably connected to the collision of continents, produced atmospheric changes that led to the greatest mass extinction in the history of multicellular life.

K.M. Meyer, M. Yu, A.B. Jost, B.M. Kelley, J.L. Payne. δ13C evidence that high primary productivity delayed recovery from end-Permian mass extinction. Earth and Planetary Science Letters, 2011; 302 (3-4): 378 DOI: 10.1016/j.epsl.2010.12.033     As described in ScienceDaily article. They found evidence that high carbon dioxide concentrations from the end-Permian volcanic eruptions caused an extended period of erosion that enriched the oceans, resulting in blooms of algae and bacteria that depleted ocean oxygen levels for as long as 5 million years and delayed the recovery of marine diversity.

J. H. Whiteside, P. D. Ward. Ammonoid diversity and disparity track episodes of chaotic carbon cycling during the early Mesozoic. Geology, 2011; 39 (2): 99 DOI: 10.1130/G31401.1     They looked at the relationship between ammonoid (squid-like shelled animals) diversity and ecosystem stability as measured by carbon isotopes, in relation to the end-Permian and end-Triassic mass extinctions. They found that swimming ammonoids (regarded as top predators, along with some fish) became extinct at these times, while some more passively floating species survived. Carbon isotope ratios fluctuated chaotically in association with the mass extinctions, implying extreme food web instability, and did not regain their stability until the evolution of new groups of swimming ammonoids some 10 million years later. They mention the importance of redundancy in top predator niches, with significant overlap in ecological space occupied by diverse species groups. The authors regard these instances as cautionary tales for the current threats to top marine predators (cod, sharks, tuna, etc.).

Randall B. Irmis, Jessica H. Whiteside. Delayed recovery of non-marine tetrapods after the end-Permian mass extinction tracks global carbon cycle. Proceedings of the Royal Society B, Published online Oct. 26, 2011; DOI: 10.1098/rspb.2011.1895     As described in a ScienceDaily article. They found that on land, in parallel with their earlier marine study, there was an extended period of ecological instability apparently resulting from low species diversity and food web connectivity. Only a few species survived the end-Permian extinction, and these had practically no competition. The resulting boom and bust population cycles prevented communities from developing stabilizing checks and balances, extending the depauperate period 8 million years into the Triassic. Dominant vertebrates included the dicynodont Lystrosaurus and procolophonids, both of which had been minor players in the Permian. Pleuromeia was a lycopod or club moss, tree or bush sized, that likewise became dominant. They did a count of individual fossils to establish this pattern, finding that 78% of terrestrial vertebrate genera went extinct. The carbon cycle did not become stable until the community structure stabilized.

Martinez, Ricardo N., et al. 2011. A basal dinosaur from the dawn of the dinosaur era in southwestern Pangaea. Science 331:206-210. They describe a new fossil, Eodromaeus murphi, from NW Argentina, and classify it as a basal theropod (predatory dinosaur).  Its contemporary, Eoraptor, they move out of the theropods, reclassifying it as a basal sauropodomorph (early predecessor of the giant, 4-legged, long-necked herbivores that were to be so diverse and abundant in the Jurassic Period). They conclude that both of those groups and the ornithiscians (the remaining dinosaur group) were established by the end of the Triassic. Their analysis of contemporary fossils also supports the idea that dinosaurs rose through a process of opportunistic replacement rather than competitive displacement, filling gaps as other groups went extinct rather than pushing them aside.

Ruhl, Micha, et al. 2011. Atmospheric carbon injection linked to end-Triassic mass extinction. Science 333:430-434. They found changes in the isotopic ratios of carbon at that time that support the idea that massive volcanic eruptions released huge amount of methane, which among other things would have a climate change effect.

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2 Comments

  1. adf said,

    October 1, 2012 at 8:42 pm

    i need more information on the lystrosaurus extinction

    • natureinquiries said,

      October 2, 2012 at 6:09 am

      I’m afraid I haven’t run across a specific account of this that I can recall. The Triassic was a time of tremendous climatic change, and of biodiversity rebounding from the mass extinction. They might have been pushed out of the picture by newly evolving specialists from other groups, or predation by emerging crocodiles and dinosaurs, or ongoing climate change, or evolving plants developing defenses they could not track. Someone may have worked this out, but I haven’t seen such an account.


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