The Weissert Event

Paleogeographic map by C.R. Scotese, PALEOMAP project. From Cavalheiro et al., 2021

The continued fragmentation of Pangaea across the Late Jurassic and Early Cretaceous led to large-scale tectonic processes, on both regional and global scale, accompanied by some of the largest volcanic episodes in the history of the Earth, eustatic oscillations of the sea level, potentially heightened levels of anoxia, oceanic stagnation, and sulphur toxicity. The Weissert Event (~133 million years ago), linked with the main magmatic activity of the Parana`-Etendeka large igneous province (LIP), represents one of the most significant paleoceanographic events of the Early Cretaceous. This global perturbation in the C cycle is marked by a positive (+1.5‰) carbon isotope excursion (CIE) observed both in organic and inorganic records.

Global mean surface temperatures (GMSTs) and associated CO2 levels. From Cavalheiro et al., 2021.

A new study analyzed deep sea sediments obtained by the Ocean Drilling Program (ODP) from offshore Antarctica to reconstruct the paleotemperatures. The international team of researchers lead by Liyenne Cavalheiro combinded calcareous nannofossil data and chemostratigraphy, and found that that global temperatures declined by 3.0 °C (±1.7 °C) during the Weissert Event.

Calcareous nannoplankton represent a major component of oceanic phytoplankton. Their calcareous skeletons can be found in fine-grained pelagic sediments in high concentrations and the biomineralization of coccoliths is a globally significant rock-forming process. Additionally, reconstructions of Cretaceous sea-surface temperatures (SSTs) have been revolutionised by the development of the organic palaeothermometer TEX86, based on the distribution of marine archaeal membrane lipids.

 

 

 

References:

Cavalheiro, L., Wagner, T., Steinig, S. et al. Impact of global cooling on Early Cretaceous high pCO₂ world during the Weissert Event. Nat Commun 12, 5411 (2021). https://doi.org/10.1038/s41467-021-25706-0

Erba, E., Bartolini, A., & Larson, R. L. (2004). Valanginian Weissert oceanic anoxic event. Geology, 32(2), 149. doi:10.1130/g20008.1 

Holz, M., Mesozoic paleogeography and paleoclimates – a discussion of the diverse greenhouse and hothouse conditions of an alien world, Journal of South American Earth Sciences (2015), doi: 10.1016/j.jsames.2015.01.001

Body and brain size evolution in genus Homo

 

Neanderthal skull (Image credit: Halamka/Getty Images)

Almost 2 million years ago in East Africa, hominin diversity reached its highest level with the appearance of the robust Paranthropus species, as well as the first specimens attributed to the genus Homo. This period is also marked by a dramatic increases in hominin body and brain size. Several theories have been developed to explain the interaction between African paleoclimate and early hominid evolution. The savannah hypothesis suggested that hominins were forced to descend from the trees and adapted to life on the savannah facilitated by walking erect on two feet. This idea was already outlined by Lamarck in his Philosophie zoologique (1809], where he describes in details how an early ancestor of primeval human abandons an arboreal life to adapt itself to open plains. More recently, the pulsed climate variability hypothesis highlights the role of short periods of extreme climate variability specific to East Africa in driving hominin evolution and subsequent dispersal events.  Now, a new study conducted by an interdisciplinary research team from Cambridge University and Tübingen University tested the influence of environmental factors on the evolution of body and brain size in the genus Homo over the last one million years.

Location and sample size (n) of body (squares) and brain size (triangles) estimates for individual Homo fossils used in the study by Will, M., Krapp, M., Stock, J.T. et al. 2021.

In the study, the team combines data from more than 300 fossils of the genus Homo divided into three taxonomic units: Mid-Pleistocene Homo, Homo neanderthalensis, and Pleistocene Homo sapiens distributed over the Old World. The environmental information for each fossil comes from a climate emulator (GCMET) that takes into account long-term, glacial-interglacial climate variation, caused by changes in the Earth’s orbit around the sun and in greenhouse gases.

The team found that temperature is a major predictor of body size variation, with larger-bodied individuals consistently occurring in colder climates. This increase in body size with decreasing environmental temperature is consistent with the Bergmann’s rule and could be explained because heat is dissipated more slowly in larger animals as the surface-area to volume ratio diminishes, so it would be a thermal advantage in colder habitats. They also found that brain size within Homo is less influenced by temperature suggesting that body and brain size are under different selective pressures.

 

References:

Will, M., Krapp, M., Stock, J.T. et al. Different environmental variables predict body and brain size evolution in Homo. Nat Commun 12, 4116 (2021). https://doi.org/10.1038/s41467-021-24290-7

Maslin M.A., C. Brierley, A. Milner, S. Shultz, M. Trauth, K. Wilson “East African climate pulses and early human evolution” Quaternary Science Reviews (2014). DOI:10.1016/j.quascirev.2014.06.012

Shultz S, Maslin M (2013) Early Human Speciation, Brain Expansion and Dispersal Influenced by African Climate Pulses. PLoS ONE 8(10): e76750. DOI: 10.1371/journal.pone.0076750

The Middle Eocene Climatic Optimum and the Patagonian floras.

Spore-pollen species from the Eocene of southern South America. From Fernandez et al., 2021

The geological records show that large and rapid global warming events occurred repeatedly during the course of Earth history. Ecological models can predict how biodiversity is affected by those events, but only the fossil record provides empirical evidence about the impact of rising temperatures and atmospheric CO2 on species diversity.

The Middle Eocene Climatic Optimum (MECO, ~40 Ma) was a transient period of global warming that interrupted the general cooling trend initiated at the end of the early Eocene climate optimum (EECO, ~49 Ma). The MECO is related to major oceanographic and climatic changes in the Neo-Tethys and also in other oceanic basins, and lasted about 500–600 Kyr. The MECO altered the pelagic ecosystem with repercussions on the food web structure. The lack of nutrients in the surface waters led to a significant decrease in planktonic foraminiferal accumulation rates, while autotroph nannoplankton accumulation rates remained stable.

Relative frequency of the most common plant groups across the MECO and Late Eocene. From Fernández et al., 2021

The MECO also influenced terrestrial biotas. A new study quantify the response of the floras of southern Patagonia to this warming event. The samples were collected from the Río Turbio Formation in southern Patagonia. The terrestrial palynological assemblage revealed a clear inverse relationship between the abundance of ferns and angiosperms. At the beginning of the MECO, ferns highly increase in abundance (with Cyatheaceae, Dicksoniaceae, and Osmundaceae as the most frequent families), while the abundance of angiosperms decreases dramatically. Podocarpaceae also increases from ~5 % to ~20%. At the core of MECO, ferns drop to a minimum, and angiosperms become dominant. Finally, at the end of the MECO ferns rise again to maximum values and angiosperms decrease.

Palynological analysis also revealed that floras in southern Patagonia were in average ~40% more diverse during the MECO than pre-MECO and post-MECO intervals. The penetration of neotropical migrant species to the highest latitudes along with the persistence of southern Gondwanan natives may have triggered the gradual increasing diversity that can be observed across the MECO.

 

References:

Fernández, D.A., Palazzesi, L., González Estebenet, M.S. et al. Impact of mid Eocene greenhouse warming on America’s southernmost floras. Commun Biol 4, 176 (2021). https://doi.org/10.1038/s42003-021-01701-5

Giorgioni, M., Jovane, L., Rego, E.S. et al. Carbon cycle instability and orbital forcing during the Middle Eocene Climatic Optimum. Sci Rep 9, 9357 (2019). https://doi.org/10.1038/s41598-019-45763-

Sonal Khanolkar, Pratul Kumar Saraswati & Karyne Rogers (2017) Ecology of foraminifera during the middle Eocene climatic optimum in Kutch, India, Geodinamica Acta, 29:2,181-193, DOI: 10.1080/09853111.2017.130084