[dinosaur] Wessex Formation (Lower Cretaceous of England) + Cretaceous continental ecosystems of Japan + more

Ben Creisler

Some recent papers on dinosaur ecosystems and environments:

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Simon J. Penn, Steven C. Sweetman, ÂDavid M. Martill & Robert A. Coram (2020)
The Wessex Formation (Wealden Group, Lower Cretaceous) of Swanage Bay, southern England.
Proceedings of the Geologists' Association (advance online publication)
doi: https://doi.org/10.1016/j.pgeola.2020.07.005
https://www.sciencedirect.com/science/article/abs/pii/S0016787820300687

The Early Cretaceous Wealden Group of Swanage Bay, Dorset, southern England, comprises two formations, a lower Wessex Formation and an overlying Vectis Formation. Presently only part of the former is exposed and here its stratigraphy, sedimentology and palaeontology are redescribed. Recent work on the Wealden Group of the Wessex Sub-basin has focused either on the Barremian -- earliest Aptian of the Isle of Wight, or on the Wealden Group of Dorset in a broader context. Consequently, the Wealden Group of Swanage Bay lacks detailed analysis and description. In the 200 years since the first account of the geology and stratigraphy of Swanage Bay, slumping and vegetation growth have dramatically concealed the upper part of the Group at this previously well-known locality. A stratigraphical framework with assigned marker beds is established here for the first time allowing for the precise placement of new palaeontological discoveries. Analysis of the palaeobotanical and microvertebrate remains recovered from the recorded section permits a more accurate reconstruction of the Early Cretaceous Wessex Formation ecosystem of east Dorset.

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Romain Amiot, Nao Kusuhashi, Haruo Saegusa, Masateru Shibata, Naoki Ikegami, Shizuo Shimojima, Teppei Sonoda, FranÃois Fourel, Tadahiro Ikedai, Christophe LÃcuyer, Marc Philippe & Xu Wang (2020)
Paleoclimate and ecology of Cretaceous continental ecosystems of Japan inferred from the stable oxygen and carbon isotope compositions of vertebrate bioapatite.
Journal of Asian Earth Sciences 104602
https://doi.org/10.1016/j.jseaes.2020.104602
https://www.sciencedirect.com/science/article/abs/pii/S1367912020303953

Highlights

We reconstruct the paleoenvironments of five Cretaceous localities in Japan.
Stable isotopes are used to infer surface temperatures and amount of precipitation.
High-altitude precipitation contributed to local surface waters.
Climate changed from cold and dry before the Aptian to warmer and more humid.

Abstract

We investigated the environmental conditions that prevailed in continental ecosystems recorded in sedimentary deposits of Japan during the Cretaceous through the analysis of oxygen and carbon isotope compositions of phosphate (Î18Op) and apatite-bound carbonate (Î18Oc and Î13Cc) of vertebrate teeth and bones. Local surface water Î18Ow values were calculated using known phosphate-water isotope fractionation equations. Anomalously low Î18Ow values of local waters strongly suggest a significant contribution of high-altitude precipitation from nearby mountains to local surface waters. Mean air temperatures were estimated using a global meteoric water Î18Omw value â Mean Annual Air Temperature relationship, and compared to surface water temperatures estimated from fish apatite Î18Op values. Local mean annual precipitations (MAP) were estimated using the known relationship existing between MAP and C3 plant Î13Cp value, the latter being calculated using apatite-diet 13C-enrichment applied to plant-eating sauropod and ornithopod dinosaur Î13Cc values. Reconstructed environmental conditions suggest that climate changed from cool temperate to warm temperate, being relatively cold and dry during the Late Hauterivian and Barremian to warmer and seasonally more humid during the Aptian and Albian, and even warmer during the Cenomanian-Coniacian. Proposed thermal evolution during the Early Cretaceous is compatible with the absence of thermophilic taxa such as crocodylomorphs before the Aptian in the fossil record of Japan.

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From earlier this year:

Free pdf:

Gabriel Andres Casal & Adriana MÃnica Nillni (2020)
MineralogÃa y geoquÃmica de huesos de dinosaurios del CretÃcico Superior del Grupo Chubut, Argentina.Â
[Mineralogy and geochemistry of dinosaur bones of the Upper Cretaceous of the Chubut Group, Argentina.]
Revista de la Sociedad GeolÃgica de EspaÃa 33(1): 11-26 (in Spanish)
ISSN 0214-2708

Free pdf:
https://sge.usal.es/archivos/REV/33(1)/RSGE33(1)_p_11_26.pdf

In this work, major and trace elements in eight pulverized samples of dinosaur bones from the Upper Cretaceous Bajo Barreal and Lago ColhuÃ Huapi formations are analyzed. Complementarily, mineralogical studies were carried out by means of petrographic microscope, electron microscope and energy-dispersive X-ray spectroscopy, in order to know the mineralogy and geochemical composition that allows interpreting the conditions and/or diagenetic processes that resulted in different preservation states of fossils. In the Bajo Barreal Formation, the alteration of the abundant volcanic glass was decisive in the permineralization of the bones and in the cementation of the rock, and also explains the greater content of major and trace elements, among them REE, that those determined in the Lago ColhuÃ Huapi Formation where pyroclasts are absent. In this last unit, the semi-arid paleoclimate determined the greatest deposition of hematite during early diagenesis. The contents of Al and Si are similar in both units but due to different factors. The degree of crystallinity of the francolite that composes the remains, the filling of the vascular cavities and the granulometry and composition of the sediment, directly intervened in the different preservation of the bones from the Bajo Barreal and Lago ColhuÃ Huapi formations.

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Fabien L. Condamine, Daniele Silvestro, Eva B. Koppelhus, and Alexandre Antonelli (2020)
The rise of angiosperms pushed conifers to decline during global cooling.
Proceedings of the National Academy of Sciences (advance online publication)
doi: https://doi.org/10.1073/pnas.2005571117
https://www.pnas.org/content/early/2020/10/27/2005571117
Free pdf:
https://www.pnas.org/content/pnas/early/2020/10/27/2005571117.full.pdf

Significance

Competition for common resources can make some species groups thrive and others decline. Flowering plants rose to dominance between 125 and 80 Ma, undergoing an explosive radiation that is believed to have impacted long-established plant groups like gymnosperms. Here, we show that the decline of conifers is strongly and directly linked to the increasing diversity of flowering plants. Both the fossil record and molecular data converge in clarifying the effects of abiotic or biotic factors on the speciation and extinction rates of conifers. These results imply that long-term biological interactions through clade competition can play a more important role in the rise and demise of major organism groups than mass extinctions.

Abstract

Competition among species and entire clades can impact species diversification and extinction, which can shape macroevolutionary patterns. The fossil record shows successive biotic turnovers such that a dominant group is replaced by another. One striking example involves the decline of gymnosperms and the rapid diversification and ecological dominance of angiosperms in the Cretaceous. It is generally believed that angiosperms outcompeted gymnosperms, but the macroevolutionary processes and alternative drivers explaining this pattern remain elusive. Using extant time trees and vetted fossil occurrences for conifers, we tested the hypotheses that clade competition or climate change led to the decline of conifers at the expense of angiosperms. Here, we find that both fossil and molecular data show high congruence in revealing 1) low diversification rates, punctuated by speciation pulses, during warming events throughout the Phanerozoic and 2) that conifer extinction increased significantly in the Mid-Cretaceous (100 to 110 Ma) and remained high ever since. Their extinction rates are best explained by the rise of angiosperms, rejecting alternative models based on either climate change or time alone. Our results support the hypothesis of an active clade replacement, implying that direct competition with angiosperms increased the extinction of conifers by pushing their remaining species diversity and dominance out of the warm tropics. This study illustrates how entire branches on the Tree of Life may actively compete for ecological dominance under changing climates.

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