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[dinosaur] Sea level regulated tetrapod diversity at Jurassic/Cretaceous + coprolites + dark cosmic cloud at K-Pg




Ben Creisler
bcreisler@gmail.com


Some recent papers:




Jonathan P. Tennant, Philip D. Mannion & Paul Upchurch (2016)
Sea level regulated tetrapod diversity dynamics through the Jurassic/Cretaceous interval.
Nature Communications 7, Article number: 12737 (2016)
doi:10.1038/ncomms12737
http://www.nature.com/articles/ncomms12737

Reconstructing deep time trends in biodiversity remains a central goal for palaeobiologists, but our understanding of the magnitude and tempo of extinctions and radiations is confounded by uneven sampling of the fossil record. In particular, the Jurassic/Cretaceous (J/K) boundary, 145 million years ago, remains poorly understood, despite an apparent minor extinction and the radiation of numerous important clades. Here we apply a rigorous subsampling approach to a comprehensive tetrapod fossil occurrence data set to assess the group’s macroevolutionary dynamics through the J/K transition. Although much of the signal is exclusively European, almost every higher tetrapod group was affected by a substantial decline across the boundary, culminating in the extinction of several important clades and the ecological release and radiation of numerous modern tetrapod groups. Variation in eustatic sea level was the primary driver of these patterns, controlling biodiversity through availability of shallow marine environments and via allopatric speciation on land.

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Martin Qvarnström, , Grzegorz Niedźwiedzki &, Živilė Žigaitė (2016)

Vertebrate coprolites (fossil faeces): An underexplored Konservat-Lagerstätte.

Earth-Science Reviews (advance online publication)

http://dx.doi.org/10.1016/j.earscirev.2016.08.014

http://www.sciencedirect.com/science/article/pii/S0012825216301283

 

 

Fossilized soft tissues of animals (e.g. muscles, hair and feathers) are valuable sources of palaeobiological information, but a poor preservation potential makes them undesirably scarce in the fossil record. The aim of this review is to summarize main findings, current progress and the analytical constraints of detecting fossilized soft tissues in coprolites from, mainly, freshwater and terrestrial carnivorous vertebrates. We conclude that soft-tissue inclusions in coprolites are sources of two important lines of information: the fossils can be put in a direct palaeoecological context, and; characters of extinct taxa are more likely preserved in the phosphate-rich taphonomic microenvironment of coprolites than elsewhere. As a result, it is possible to unravel the deep-time origins of host-parasite relations, to understand ancient trophic food webs and detect new soft-tissue characters of different animal groups. Examples of the latter include muscle tissues from a tyrannosaurid prey, tapeworm eggs (including a developing embryo) in a Permian shark coprolite, as well as hair from multituberculates and, probably, from stem-mammals (Therapsids). Additionally, the use of coprolites in an archaeological context is briefly reviewed with focus on key aspects that may become implemented in studies of pre-Quaternary specimens as well. In sum, there is a wide range of information that can be extracted from coprolites, which has not yet been fully explored in palaeontological studies.

 


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Free pdf:

Tokuhiro Nimura, Toshikazu Ebisuzaki & Shigenori Maruyama (2016)
End-Cretaceous cooling and mass extinction driven by a dark cloud encounter.
Gondwana Research 37: 301-307
http://dx.doi.org/10.1016/j.gr.2015.12.004
http://www.sciencedirect.com/science/article/pii/S1342937X16000253


Highlights

The dark cloud encounter drove the End-Cretaceous cooling and mass extinction.
The evidence of an dark cloud encounter was found in a pelagic sediment core.
A broad iridium anomaly suggests extraterrestrial flux were enhanced for 8 Myr.
A novel method to measure the extraterrestrial flux was proposed.

Abstract

We have identified iridium in an ~ 5 m-thick section of pelagic sediment cored in the deep sea floor at Site 886C, in addition to a distinct spike in iridium at the K–Pg boundary related to the Chicxulub asteroid impact. We distinguish the contribution of the extraterrestrial matter in the sediments from those of the terrestrial matter through a Co–Ir diagram, calling it the “extraterrestrial index” fEX. This new index reveals a broad iridium anomaly around the Chicxulub spike. Any mixtures of materials on the surface of the Earth cannot explain the broad iridium component. On the other hand, we find that an encounter of the solar system with a giant molecular cloud can aptly explain the component, especially if the molecular cloud has a size of ~ 100 pc and the central density of over 2000 protons/cm3. Kataoka et al. (2013, 2014) pointed that an encounter with a dark cloud would drive an environmental catastrophe leading to mass extinction. Solid particles from the hypothesized dark cloud would combine with the global environment of Earth, remaining in the stratosphere for at least several months or years. With a sunshield effect estimated to be as large as − 9.3 W m− 2, the dark cloud would have caused global climate cooling in the last 8 Myr of the Cretaceous period, consistent with the variations of stable isotope ratios in oxygen (Barrera and Huber, 1990; Li and Keller, 1998; Barrera and Savin, 1999; Li and Keller, 1999) and strontium (Barrera and Huber, 1990; Ingram, 1995; Sugarman et al., 1995). The resulting growth of the continental ice sheet also resulted in a regression of the sea level. The global cooling, which appears to be associated with a decrease in the diversity of fossils, eventually led to the mass extinction at the K–Pg boundary.

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