What was one ecological change that occurred following the permian mass extinction?

Abstract

Mass extinction events are considered here to be: (1) biodiversity crises, determined primarily by significantly increased extinction rates, and (2) ecological (or biotic) crises, when the ecosystem consequences of the biospheric perturbation were disproportionately large when compared to the protracted/stepwise biodiversity loss alone. Only the end-Permian and end-Cretaceous mass extinctions were unequivocal mass extinctions sensu stricto. The end-Ordovician global event was only a major biodiversity crisis, whereas the Late Devonian and end-Triassic extinctions were major ecological (or biotic) crises. In the causal context, the end-Cretaceous catastrophe could have been caused by the impact of a giant meteorite, but most probably this was only a final step leading to the collapse of the biosphere, influenced earlier by Deccan trap volcanism. Four other mass extinctions are more (Mesozoic) or less (Paleozoic) certainly connected with Earth-bound destructive factors, with large igneous provinces as a leading proposed trigger. The volcanic greenhouse/icehouse scenario has been updated and is supported by recently discovered mercury anomalies. A wide spectrum of killing factors related to volcanic cataclysm, and augmented by non-volcanic factors, has operated within a totally different time scale. The concrete interrelationships and feedbacks were certainly specific for each of the mass extinctions, resulting in their inhomogeneity.

Temporal and Biogeographic Scales of Mass Extinctions

Mass extinctions were defined subjectively as short periods of Earth history during which rates of extinction reached exceptionally high levels in widespread areas. In evolutionary terms, how short is short? In studies of recent extinctions in which events are followed on an ecological timescale, short periods of time are measured in terms of years, decades, centuries, or possibly a millennium or two. A recent compilation of recent estimated durations of the last three of the “Big Five” mass extinctions revealed values as much as 8.3 Ma to as short as less than a year (Barnosky et al., 2011).

Current radiometric methods for determining ages and durations of pre-Quaternary events lack the degree of resolution found in ecological studies of the modern biota. For example, using the 40Ar/39Ar method of age determination, which is one of the most precise methods of radiometric age determination available for pre-Quaternary deposits, the age of the Cretaceous–Tertiary boundary, as recognized in nonmarine sediments in eastern Montana, is placed at 65.58±0.04 Ma (Wilson, 2005). As data on extinctions of Cretaceous lineages of nonmarine and marine organisms are collected and correlated, all extinction events that occurred within an interval of 80,000 years would necessarily be treated as having occurred simultaneously. Recognition of the role of short-term modifications of the biota on an ecological timescale and their consequences in terms of background and mass extinctions on a geological timescale remains a major challenge.

In comparison to the fossil record of marine invertebrates, which is the foundation for studies of the role of mass extinctions in evolution, the fossil record of terrestrial vertebrates is much more limited, particularly in its biogeographic coverage. For example, detailed records of mammalian evolution across the Cretaceous–Tertiary boundary are limited to sites in the Western Interior of North America (Archibald, 2011). Significant gaps in the fossil records of mammalian evolution in Eurasia and the continents of the Southern Hemisphere characterize this interval. One consequence of these gaps is the uncertainty in determining the origins of mammalian groups that appear soon after a mass extinction event. Were they descendants of a few local survivors or immigrants from another less impacted and yet to be sampled area?

Implications for Hyperthermals

The EPME shared many similarities with the end-Triassic mass extinction and the smaller Guadalupian and Toarcian extinctions. Why was the EPME, at least in the oceans, more severe than those other crises? Why did other hyperthermals, such as the PETM, trigger only limited extinction? This question is one of the most exciting ongoing issues in the study of extinctions, and is unlikely to have a simple solution. It seems likely that the total magnitude of environmental change was greater during the EPME, at least as inferred from geochemical proxy records. It is less clear, however, whether the rate of environmental disruption was also more rapid during the EPME. Organisms are able to acclimatize or adapt to withstand stressful conditions, but faster rates of change may overwhelm those capabilities. However, reconstructing the rate of environmental change during deep-time extinctions, especially at timescales relevant to biological adaptation, is extremely challenging. Other differences in the Earth system may explain some of the different outcomes. The mid-Mesozoic development of a deep-sea reservoir of carbonate sediment would have reduced fluctuations in ocean chemistry during hyperthermals, for example. Finally, successive extinctions had progressively eliminated marine organisms that were most vulnerable to hyperthermals, potentially reducing the consequences of geologically-younger events. The severity of the end-Permian mass extinction likely arose from an unfortunate confluence of these factors, but understanding why environmental perturbation leads to extinction is crucial for predicting the consequences of hyperthermals, including the ongoing hyperthermal driven by anthropogenic climate change.

II.C. Temporal Scale of Mass Extinctions

Mass extinctions were intentionally defined subjectively as short periods of Earth history during which rates of extinction reached exceptionally high levels. In geological terms, how short is short? In studies of recent extinctions in which events are followed on an ecological timescale, short periods of time are measured in terms of years, decades, centuries, or possibly a millennium or two. Current radiometric methods for determining ages and durations of pre-Quaternary events lack this level of resolution. For example, using the 40Ar/39Ar method of age determination, which is the most precise method of radiometric age determination available for pre-Quaternary deposits, the age of the Cretaceous-Tertiary boundary is placed at 65.16 ± 0.04 Ma. As data on extinctions of Cretaceous lineages of marine and nonmarine organisms are collected and correlated, all extinction events that occurred within an interval of 80,000 years would necessarily be treated as having occurred simultaneously. The farther one goes back in Earth history, the longer the error bars become; for example, some paleontologists currently argue that the extinctions of lineages that comprise the Permian-Triassic mass extinction might have occurred over an interval of 1 or 2 million years.

Ecological Severity of the Extinctions

Mass extinctions are most often evaluated in terms of biodiversity crashes. However, they have also been analyzed in terms of their ecological severity. In a widely cited scheme of ecological severity, the marine TJB extinction was evaluated as category IIa and the nonmarine TJB extinction as category I or IIa. Category I indicates that ecosystems before the extinction were replaced by new ecosystems post-extinction, whereas category IIa indicates that the extinctions caused the permanent loss of major ecosystem components.

Rating the TJB marine extinction as category IIa was largely based on a perceived global reef extinction. However, as discussed above, this disruption was not demonstrably global, and it was definitely temporary. Therefore, the TJB marine extinction should be downgraded to category IIb, which means that the disruption was temporary; i.e., the reef ecosystem re-established itself after a hiatus.

It has long been claimed that the TJB transition involved a rapid ecological replacement of Triassic “mammal-like reptiles” (synapsids) and rhynchosaurs by dinosaurs. However, rhynchosaurs and dicynodont synapsids are known from strata no younger than Norian. The other principal group of Late Triassic synapsids, the cynodonts, were of low diversity after the Carnian (see above). The oldest record of dinosaur body fossils is Carnian, and dinosaurs began to diversify substantially in some parts of Pangea by the late Norian. Thus, the ecological severity of the end-Triassic tetrapod extinction is relatively low (Category IIb), and there are also no extensive plant extinctions across the TJB. Clearly, the terrestrial ecosystem was disrupted across the TJB, but it was not a severe disruption.

Trophic systems in the sea and on the land did not collapse across the TJB. There was no mass extinction of the oceanic plankton across the TJB, so there also was no collapse of marine food chains. Similarly, the lack of a mass extinction of land plants makes it difficult to envision a collapse of the metazoan trophic structure that relied on plants as the primary sources of food.

What happened after the Permian mass extinction?

What major changes happened on Earth's surface during Permian period?

What changes occurred in the Earth leading up to the Permian Extinction with volcanoes?

What major event happened at the end of the Permian period?