January 26, 2023

The Reign of the Dinosaurs Ended in Spring: Revelations From Bones of Fish That Died When the Asteroid Hit

The asteroid that eliminated nearly all dinosaurs struck Earth throughout spring. A global team of scientists from the Vrije Universiteit (VU) Amsterdam (The Netherlands), Uppsala University (Sweden), Vrije Universiteit Brussel (Belgium) and the ESRF, the European Synchrotron (France), has identified when the meteorite crashed onto the Earth, after examining the remains of fishes that died just after the impact. Their results are released in the journal Nature today.
Around 66 million years earlier, the so-called Chicxulub meteorite crashed into the Earth, in what today is the Yucatán peninsula in Mexico, marking the death of dinosaurs and end of the Cretaceous duration. This mass extinction still puzzles scientists today, as it was among the most selective in the history of life: all non-avian dinosaurs, pterosaurs, ammonites, and many marine reptiles vanished, whilst mammals, turtles, birds, and crocodiles made it through.

When the meteorite impacted Earth, it rocked the continental plate and caused substantial waves in water bodies, such as lakes and rivers. These moved massive volumes of sediment that swallowed up fish and buried them alive, while impact spherules (glass beads of Earth rock) rained below the sky, less than an hour after impact. Today, the occasion deposit of Tanis in North Dakota (United States) maintains a fossilized ecosystem that includes sturgeons and paddlefishes, which were direct casualties of the event.
The fossil fishes were remarkably protected, with their bones showing practically no indications of geochemical modification. Melanie During, scientist from Uppsala University and the VU Amsterdam and lead author of the publication, went onsite to excavate the valuable specimens: “It was apparent to us that we required to examine these bones to get important info about the minute of the effect,” she describes.
Creative restoration of the Seiche wave surging into the Tanis river, bringing in fishes and whatever in its course (dinosaurs, trees) while impact spherules drizzle down from the sky. Ants try to get back into their nest as the just blooming dianthus in the foreground are already being affected by the impact spherules.
The team came to the ESRF, a particle accelerator that produces the worlds brightest x-rays, with a partial fish specimen and representative sections of the bones and brought out high-resolution synchrotron X-ray tomography.
The ESRF is the best tool to research study this type of sample and the center has established unique know-how in paleontology over the last 20 years. “Thanks to the ESRFs information, we discovered that the bones signed up seasonal growth, quite like trees do, growing a brand-new layer every year on the outside of the bone,” discusses Sophie Sanchez of Uppsala University, and visiting researcher at the ESRF.
A paddlefish from Tanis, prior to scanning at the ESRF. On the right, the rostrum (paddle) is missing and on the left everything behind the shoulder fin is missing out on. Credit: During et al.
” The obtained development rings not only recorded the biography of the fishes however likewise taped the most recent Cretaceous seasonality and therefore the season in which the catastrophic extinction happened,” mentions senior author Jeroen van der Lubbe of the VU in Amsterdam.
The X-ray scans also showed the circulation, shapes, and sizes of the bone cells, which are understood to vary with the seasons. “In all studied fishes, bone cell density and volumes can be traced over multiple years and they suggest whether it was spring, autumn, winter season, or summertime. We saw that both cell density and volumes were on the rise however had not yet peaked during the year of death, which suggests that growth quickly stopped spring” says Dennis Voeten, scientist at Uppsala University.
A virtual thin section of a paddlefish jawbone with the bone cell (white dots) variation over numerous years with the carbon isotope ratio (from the same bone). Blue equates to winter season and low carbon 13 (and low bone cell density) and yellow equals summer season and high carbon 13 (and high bone density).
In parallel to synchrotron radiation studies, the team brought out carbon isotope analysis to expose the annual feeding pattern of a fish. “The carbon isotope signal throughout the growth record of this unfortunate paddlefish confirms that the feeding season had actually not yet climaxed– death came in spring,” asserts During.
Melanie During gone to the Tanis site in August 2017 to excavate the paddlefishes and sturgeons. Credit: Jackson Leibach
The findings will aid future research study into the selectivity of the mass extinction: in the Northern Hemisphere, it was spring and therefore the reproduction cycles of organisms were beginning, just to be abruptly stopped. It was fall in the Southern Hemisphere, where numerous organisms were likely preparing for winter season. In general, it is well understood that organisms that were exposed passed away practically right away. Those sheltering in caves or burrows due to the fact that they were hibernating were far more likely to make it through into the Paleogene. “Our results will assist to reveal why many of the dinosaurs passed away out while birds and early mammals handled to avert extinction,” concludes During.
Recommendation: “The Mesozoic terminated in boreal spring” 23 February 2022, Nature.DOI: 10.1038/ s41586-022-04446-1.

An international group of researchers from the Vrije Universiteit (VU) Amsterdam (The Netherlands), Uppsala University (Sweden), Vrije Universiteit Brussel (Belgium) and the ESRF, the European Synchrotron (France), has figured out when the meteorite crashed onto the Earth, after examining the remains of fishes that passed away simply after the impact. These moved enormous volumes of sediment that swallowed up fish and buried them alive, while impact spherules (glass beads of Earth rock) rained down from the sky, less than an hour after effect. Creative restoration of the Seiche wave surging into the Tanis river, bringing in fishes and everything in its course (dinosaurs, trees) while effect spherules drizzle down from the sky. “In all studied fishes, bone cell density and volumes can be traced over numerous years and they show whether it was spring, winter, summer, or fall. In parallel to synchrotron radiation studies, the group carried out carbon isotope analysis to expose the yearly feeding pattern of a fish.

A group of researchers from the Vrije Universiteit, Uppsala University, and the ESRF has now clarified the circumstances surrounding the diverse extinction across the different groups. The answers originated from the bones of fishes that passed away minutes after the meteorite struck.

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