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[dinosaur] End-Permian marine mass extinction overestimated + Late Cretaceous cooling + monitor skull

Ben Creisler

Some recent non-dino papers:

Steven M. Stanley (2016)
Estimates of the magnitudes of major marine mass extinctions in earth history.
Proceedings of the National Academy of Sciences (advance online publication) 
DOI: 10.1073/pnas.1613094113


This paper shows that background extinction definitely preceded mass extinctions; introduces a mathematical method for estimating the amount of this background extinction and, by subtracting it from total extinction, correcting estimates of losses in mass extinctions; presents a method for estimating the amount of erroneous backward smearing of extinctions from mass extinction intervals; and introduces a method for calculating species losses in a mass extinction that takes into account clustering of losses. It concludes that the great terminal Permian crisis eliminated only about 81% of marine species, not the frequently quoted 90–96%. Life did not almost disappear at the end of the Permian, as has often been asserted.


Procedures introduced here make it possible, first, to show that background (piecemeal) extinction is recorded throughout geologic stages and substages (not all extinction has occurred suddenly at the ends of such intervals); second, to separate out background extinction from mass extinction for a major crisis in earth history; and third, to correct for clustering of extinctions when using the rarefaction method to estimate the percentage of species lost in a mass extinction. Also presented here is a method for estimating the magnitude of the Signor–Lipps effect, which is the incorrect assignment of extinctions that occurred during a crisis to an interval preceding the crisis because of the incompleteness of the fossil record. Estimates for the magnitudes of mass extinctions presented here are in most cases lower than those previously published. They indicate that only~81% of marine species died out in the great terminal Permian crisis, whereas levels of 90–96% have frequently been quoted in the literature. Calculations of the latter numbers were incorrectly based on combined data for the Middle and Late Permian mass extinctions. About 90 orders and more than 220 families of marine animals survived the terminal Permian crisis, and they embodied an enormous amount of morphological, physiological, and ecological diversity. Life did not nearly disappear at the end of the Permian, as has often been claimed.





Clay R. Tabor, Christopher J. Poulsen, Daniel J. Lunt, Nan A. Rosenbloom, Bette L. Otto-Bliesner, Paul J. Markwick, Esther C. Brady, Alexander Farnsworth and Ran Feng (2016)2
The cause of Late Cretaceous cooling: A multimodel-proxy comparison.
Geology (advance online publication)
doi: 10.1130/G38363.1

Proxy temperature reconstructions indicate a dramatic cooling from the Cenomanian to Maastrichtian. However, the spatial extent of and mechanisms responsible for this cooling remain uncertain, given simultaneous climatic influences of tectonic and greenhouse gas changes through the Late Cretaceous. Here we compare several climate simulations of the Cretaceous using two different Earth system models with a compilation of sea-surface temperature proxies from the Cenomanian and Maastrichtian to better understand Late Cretaceous climate change. In general, surface temperature responses are consistent between models, lending confidence to our findings. Our comparison of proxies and models confirms that Late Cretaceous cooling was a widespread phenomenon and likely due to a reduction in greenhouse gas concentrations in excess of a halving of CO2, not changes in paleogeography.


Gabrielle H. Openshaw, Domenic C. D'Amore, Marta Vidal-García and J. Scott Keogh (2016)

Combining geometric morphometric analyses of multiple 2D observation views improves interpretation of evolutionary allometry and shape diversification in monitor lizard (Varanus) crania.

Biological Journal of the Linnean Society (advance online publication)

DOI: 10.1111/bij.12899



Geometric morphometrics is a powerful tool for the quantification, visualization and analysis of morphological variation and change. This approach is being applied more frequently in a phylogenetic comparative context to assess the relative influence of size, ecology, function, and developmental constraints on morphological evolution. Geometric morphometric methods rely on homologous landmarks as the source of shape data, and the level of detail and accuracy increases with the amount of information contained in a landmark configuration. It may be possible, however, to capture particular elements of shape variation by concentrating on different observation angles of a complex structure like the vertebrate cranium. Our study examines how observation view (dorsal, ventral and lateral) influences 2D geometric morphometric analysis of interspecific cranial shape variation in monitor lizards. We recover a strong phylogenetic signal in all three views and general concordance in patterns of size-corrected shape diversification within the genus. We also find subtle, but important differences, however, among views in analyses of evolutionary allometry and shape variation, which may reflect both landmark configuration design and adaptive functional trends of the study system. Our study shows that studies restricted to a 2D geometric morphometric analysis of a complex 3D biological structure can combine carefully designed 2D landmark configurations describing alternative planes to maximize shape coverage.