Written by Ethan Thio '22
Edited by Elana Balch '21.5
The extinction of the dinosaurs is a well-known, epochal moment in the history of our planet. It orients geological timescales and occupies an outsized role in the popular imagination in everything from Jurassic Park to natural history museums. The hypotheses behind its cause range from the widely accepted view, of an asteroid impact wiping out the dinosaurs, to more contested theories such as colossal volcanic eruptions that decimated the dinosaurs. The fact that scientific dissent exists around an event of this magnitude reveals a crucial truth about any theories and conclusions made about the period - that definitive evidence to resolve doubt is exceedingly rare. In what is known as the Tertiary Period, researchers posit that the extinction of the dinosaurs eliminated a major source of competition that allowed for the growth and dominance of mammalian creatures, flowering plants, insects, and many of the organisms that inhabit our present world. But fossil evidence of the period immediately following the extinction of the dinosaurs that could bolster these hypotheses isn't fully comprehensive, often containing gaps in sediment accumulation that leave some periods of time following the extinction event unaccounted for. New research in the journal Science points to a discovery of fossil records in Corral Bluffs, a fossil site in Colorado, which contains a fully continuous fossil record of the first few million years after the extinction of the dinosaurs.
The Coral Bluffs record supports the wider consensus arguing that an extinction-level event occurred, noting that for 1000 years after, animals and plant species were exceedingly rare and small in size. Ecosystem recovery advanced over significant timescales, taking 200,000 years for palm-based forests and accompanying larger animals to arise. As larger animals began to arise, more diverse plant species also did, such as legume plants containing peas or beans. The arrival of legumes was an important milestone in ecosystem recovery, as they provide a calorie-dense food source that could support larger mammalian creatures and greater biodiversity. Broadly, the Coral Bluffs fossil record supports the hypothesis that the extinction of the dinosaurs allowed for new mammalian and plant species to take the mantle, but this recovery and diversification from the initial set of small mammals and limited variety of plants took hundreds of thousands of years.
The fossil record also allows for new analysis of the role of climate and its influence on the broader ecosystem recovery following the extinction event. Leaves were encountered in the Coral Bluffs fossil evidence, and the presence of smooth-edged leaves, common in warmer periods, allowed the researchers to conclude that there were three distinct warming periods in the time period encompassed by the fossil record. The timing of these warming intervals coincided with greater biodiversity, meaning that as climates warmed, new species and adaptations arose and thrived. For example, plants were observed to form larger, wingless seeds instead of smaller, winged seeds that had defined earlier plant species. This was hypothesized to correlate with a shift from seed transport over wind to seed transport by animal species, as the latter became more prevalent with broader ecosystem recovery. These adaptations catalyzed adaptations in other species, creating a sort of feedback loop that continued to fuel increasing biodiversity.
The discovery of this fossilized evidence in the Coral Bluffs provides some of the most exhaustive proof science has for how ecosystems recover from a mass extinction level event. Smaller animals and plants are the only organisms able to survive in a nutrient-scarce, unstable, post-extinction environment, slowly bringing rise to larger species with new adaptations to the specific ecological conditions of the period and area. The significance of these findings should not be taken lightly. The reemergence of biodiverse ecosystems took approximately one million years, around five times the length of time that modern Homo sapiens have existed. In a world where humanity is having an increasingly profound effect on the natural environment, it remains natural to believe that the environment that has always existed throughout human history will continue to persist into the future. But the reality is that despite the resilience of natural ecosystems, and the high probability of life existing in some form regardless of human activity, the Coral Bluffs fossil record is significant proof of how short-term, violent events can initiate lengthy, profound environmental and ecological change. Current human activity does not only impact the near future, it will have a remarkable effect on the ecosystems and environments of the distant future, only heightening the significance and necessity for meaningful change and environmental reform in the present.
Lyson T.R., Miler I.M., Bercovici I.M., Weissenburger K., Fuentes A., Clyde W., Hagadorn J., Butrim M. (2019). Exceptional continental record of biotic recovery after the Cretaceous–Paleogene mass extinction. Science (2019)
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Picture Credit: Jebulon, Wikimedia Commons, Accessible at https://commons.wikimedia.org/wiki/File:Allosaurus_fragilis_moulage_MNHN_paleontologie_1.JPG