Dinosaurs disappeared from Earth 66 million years ago. The mass extinction of the clade was theorized to be initiated by a massive space rock that crashed to the face of our planet. In a new study, the event, also known as the Chicxulub impact, was confirmed to have occurred during the spring season.

Chicxulub Mass Extinction Happened in Spring 66 Million Years Ago

Osteohistological thin sections of five acipenseriform fishes.
(Photo: Nature)
a–e, Thin sections in transmitted light of VUA.GG.2017.MDX-3 (a), VUA.GG.2017.X-2743M (b), VUA.GG.2017.X-2744M (c), VUA.GG.2017.X-2733A (d) and VUA.GG.2017.X-2733B (e), showing congruent pacing of bone apposition during the final years of life, terminating in spring. Red arrows indicate LAGs. Scale bars, 0.5 mm.

The study involved six fossils of fish species obliterated in 60 minutes after the Chicxulub impact. The remains were recovered in North Dakota's Tanis site. The study was made possible through scholars from the University of Manchester. According to their findings, the exact time when the asteroid slammed to Earth was in spring 66 million years ago.

The research was the first to support the most plausible time of impact suggested by a separate study. According to the authors, the catastrophe happened when the northern and southern hemisphere was under the spring and autumn season, respectively.

Uppsala University's Evolutionary Biology Centre expert and lead author of the study Melanie During said in a DailyMail report that cold-blooded fishes are composed of bone structures that grow similar to how trees develop, accumulating new layers every year during their lifetime.

Through the help of the European Synchrotron Radiation Facility (ESRF), the team could scan the thin sections of the fish bone layers for cell fluctuations. Based on the data, all of the observed subjects died simultaneously, particularly during spring, During explained.

The fish bones, according to During, had subtle variances in their features that can specify timelines of their development. In the study, the fish were identified to eat a little in springtime, a lot in summer, less in autumn, and stop consuming in winter.

The growth of the fishes began in spring and was accelerated during summer. In autumn, they slow down on growing, and in winter, they ultimately stop.

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Mass Extinction Evidence in Fish

There were many effects of the Chicxulub impact that was relayed to the planet and its early residents. Among those effects were huge dust clouds following the touchdown of the asteroid. The aerial factor caused an atmospheric disturbance that resulted in a global climate shift. The aftermath wiped out almost 75 percent of the prehistoric fauna and flora from our planet.

The Chicxulub mass extinction event killed most non-avian dinosaurs, marine reptiles, pterosaurs, and ammonites. After the disappearance of most creatures, only a few mammalians, reptilians, and avians survived.

The asteroid impact in the Yucatan extremely shocked the planet to the point that towering tsunamis came crashing across the epicenter's neighboring continents. The massive waves caused sediments and spherules to bury many fishes alive. The study's specimens, the sturgeons, and paddlefishes were among the Chicxulub's direct casualties.

In addition to the bones, the fossilized fishes that were identified are commonly eating zooplanktons. The microorganisms enriched the fish bones over time. According to the authors, the zooplankton peak during summer, but the carbon isotope data showed that the eating pattern in the fishes did not reach climax due to their death in spring.

The study was published in Nature, titled "The Mesozoic terminated in boreal spring."

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