More Like this

1. The end-Cretaceous plant extinction: Heterogeneity, ecosystem transformation, and insights for the future

   https://doi.org/10.1017/ext.2023.13  

   Wilf, Peter; Carvalho, Mónica R; Stiles, Elena (January 2023, Cambridge Prisms: Extinction)

   Abstract The Cretaceous–Paleogene (K–Pg) mass extinction was geologically instantaneous, causing the most drastic extinction rates in Earth’s History. The rapid species losses and environmental destruction from the Chicxulub impact at 66.02 Ma made the K–Pg the most comparable past event to today’s projected “sixth” mass extinction. The extinction famously eliminated major clades of animals and plankton. However, for land plants, losses primarily occurred among species observed in regional studies but left no global trace at the family or major-clade level, leading to questions about whether there was a significant K–Pg plant extinction. We review emerging paleobotanical data from the Americas and argue that the evidence strongly favors profound (generally >50%), geographically heterogeneous species losses and recovery consistent with mass extinction. The heterogeneity appears to reflect several factors, including distance from the impact site and marine and latitudinal buffering of the impact winter. The ensuing transformations have affected all land life, including true angiosperm dominance in the world’s forests, the birth of the hyperdiverse Neotropical rainforest biome, and evolutionary radiations leading to many crown angiosperm clades. Although the worst outcomes are still preventable, the sixth mass extinction could mirror the K–Pg event by eliminating comparable numbers of plant species in a geologic instant, impoverishing and eventually transforming terrestrial ecosystems while having little effect on global plant-family diversity. 

   more » « less
2. Intense Changes in the Main Source of Organic Carbon to the Gulf Coastal Plain Following the Cretaceous‐Paleogene Boundary

   https://doi.org/10.1029/2024PA004887  

   Sosa‐Montes_de_Oca, C; Witts, J D; Lowery, C M; Kearns, L E; Garb, M P; Naujokaityte, J; Myers, C E; Landman, N H; Pancost, R D (August 2024, Paleoceanography and Paleoclimatology)

   Abstract To explore both environmental change and the response of non‐fossilizing phytoplankton across the Cretaceous‐Paleogene (K‐Pg) boundary mass extinction event, we determined changes in organic matter (OM) sources using a range of apolar (n‐alkanes, acyclic isoprenoids, steranes, and hopanes) and polar (BIT index) biomarkers. We analyzed two K‐Pg proximal sections, located in the Mississippi Embayment, Gulf Coastal Plain (USA), covering ∼300 kyrs prior to and ∼3 myrs after the K‐Pg event. The OM abundance and composition changed dramatically across the boundary. The post‐impact ejecta layer and burrowed unit are characterized by an increase in the mass accumulation rate (MAR) of plant and soil biomarkers, including high‐molecular‐weightn‐alkanes and C₂₉steranes as well as the BIT index, related to an erosive period which transported terrestrial OM to the ocean in the aftermath of the impact event. At the same time, MARs of putative aquatic biomarkers decrease (low‐molecular‐weightn‐alkanes, C₂₇steranes and pristane and phytane), which suggests a collapse of the marine phytoplankton community. The increase of terrestrial OM to the ocean, during the first 280 kyrs after the Chicxulub impact event, is a combination of reworked kerogen, soil and some plant material. Crucially, within the latter part of this erosion period, only ∼160 kyrs after the K‐Pg do biomarkers return to distributions similar to those in the upper Cretaceous, although not to pre‐impact MARs. Thus, our results suggest a long‐term interval for the full sedimentary and ecological recovery of the non‐fossilizing phytoplankton community after this event. 

   more » « less
3. Shifts in trophic architecture and ecospace stability determining survivorship and extinction at the end-Cretaceous

   Chiarenza, Alfio Alessandro; García-Girón, Jorge; Alahuhta, Janne; DeMar, D. G.; Jani, Heino; Mannion, P. D.; Williamson, T. E.; Wilson Mantilla, G. P.; Brusatte, S. L. (November 2022, Journal of Vertebrate Paleontology)

   An explanation for why some species, such as non-avian dinosaurs, became extinct, whereas others, including mammals, survived the Cretaceous/Paleogene (K/Pg) mass extinction, 66 million years ago (Ma) is still debated. What were the mechanisms behind community restructuring and the emergence of new ecological opportunities after the K/Pg event, selectively driving extinction and survivorship patterns? Using Markov networks, ecological niche partitioning and Earth System models, we reconstructed disruptions in continental food web dynamics, simulating long-term trajectories in ecospace occupancy through the latest Cretaceous (83.6–66.0 Ma) and early Paleogene (66.0–61.6 Ma). This method uses partial correlation networks to represent how different trophic groups interact in a food web and builds on empirical spatial co-variations to explore dependencies between trophic groups. Our analyses are based on a spatiotemporally and taxonomically standardized dataset, comprising more than 1,600 fossil occurrences representing more than 470 genera of fish, salamanders, frogs, albanerpetontids, lizards, snakes, champsosaurs, turtles, crocodylians, dinosaurs (including birds), and mammals across the best sampled region for this interval, the Western Interior of North America. We explicitly tested whether: 1) shifts in food web architecture underwent major restructuring before and after the K/Pg transition, including whether some trophic guilds were more prone to these shifts than others; and 2) any of these changes were associated with fluctuations in the realized niche space, helping to explain survivorship and extinction patterns at the boundary. We find a shift in latest Cretaceous dinosaur faunas, as medium-sized species counterbalanced a loss of large herbivores, but that dinosaur niches were otherwise resilient and static until the K/Pg boundary. Smaller terrestrial vertebrates, including mammals, followed a consistent trajectory of increasing trophic impact and relaxation of ecological niche limits that began in the Cretaceous and continued after the extinction. Patterns of mammalian ecological radiation and niche restructuring indicate that these taxa did not simply proliferate after the extinction; rather, their earlier ecological diversification might have helped them survive the K/Pg event, whereas the static niche of dinosaurs might have contributed to their demise. 

   more » « less
4. Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact

   https://doi.org/10.1073/pnas.1905989116  

   Henehan, M. J..; Ridgwell, A.; Thomas, E.; Zhang, S.; Alegret, L.; Schmidt, D. N.; Rae, J. W.; Witts, J. D.; Landman, N. H.; Greene, S. E.; et al (November 2019, Proceedings of the National Academy of Sciences of the United States of America)

   Mass extinction at the Cretaceous–Paleogene (K-Pg) boundary coin- cides with the Chicxulub bolide impact and also falls within the broader time frame of Deccan trap emplacement. Critically, though, empirical evidence as to how either of these factors could have driven observed extinction patterns and carbon cycle perturbations is still lacking. Here, using boron isotopes in foraminifera, we docu- ment a geologically rapid surface-ocean pH drop following the Chicxulub impact, supporting impact-induced ocean acidification as a mechanism for ecological collapse in the marine realm. Subsequently, surface water pH rebounded sharply with the extinction of marine calcifiers and the associated imbalance in the global carbon cycle. Our reconstructed water-column pH gradients, combined with Earth sys- tem modeling, indicate that a partial ∼50% reduction in global ma- rine primary productivity is sufficient to explain observed marine carbon isotope patterns at the K-Pg, due to the underlying action of the solubility pump. While primary productivity recovered within a few tens of thousands of years, inefficiency in carbon export to the deep sea lasted much longer. This phased recovery scenario recon- ciles competing hypotheses previously put forward to explain the K-Pg carbon isotope records, and explains both spatially variable patterns of change in marine productivity across the event and a lack of extinction at the deep sea floor. In sum, we provide insights into the drivers of the last mass extinction, the recovery of marine carbon cycling in a postextinction world, and the way in which ma- rine life imprints its isotopic signal onto the geological record. 

   more » « less
5. Globally distributed iridium layer preserved within the Chicxulub impact structure

   https://doi.org/10.1126/sciadv.abe3647  

   Goderis, Steven; Sato, Honami; Ferrière, Ludovic; Schmitz, Birger; Burney, David; Kaskes, Pim; Vellekoop, Johan; Wittmann, Axel; Schulz, Toni; Chernonozhkin, Stepan M.; et al (February 2021, Science Advances)

   null (Ed.)

   The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide. 

   more » « less