Fish bones and water lilies help pin down the month the dinosaurs died

The dinosaurs were killed by a meteorite impact 66 million years ago. There has been debate among paleontology enthusiasts about when this happened.

Evidence shows that the dinosaurs probably died in June. The fact that researchers have been able to identify the exact time of an event millions of years ago is a remarkable feat of science.

The site called Tanis is located in the Hell Creek Formation in North Dakota. Tanis is one of several geological locations around the world where scientists have observed the boundary of the dinosaurs.

Dinosaurs, early mammals, fish, plants and other things have been found in Tanis. Many of the fossils are well preserved, with some showing soft tissues, such as skin and bones, which can offer valuable scientific insights.

The Tanis site has been the focus of research by Robert DePalma since 2008. DePalma and his colleagues argued that Tanis captured the moment of the asteroid's impact due to three factors.

The first was the presence of dinosaur fossils that were present right up to the boundary at the time of impact.

There was a layer of melt spherules, tiny glass balls that cooled in flight from molten rock. When the asteroid hit Earth, it spread debris and melted spherules for thousands of kilometers.

There was evidence of seiche waves in deep channels. The Tanis site was located on the coast of the western interior seaway at the end of the Cretaceous period, with sea levels 200 meters higher than they are today. The site was estuarine, which means fresh and salt waters were mingling.

The seiche waves were generated by the distant impact in Mexico, which set off seismic waves that shook the Earth and caused water to flow in and out of the river channels at a fast rate.

The researchers found abundant spherules in the gill skeletons of some of the fish they examined. They could have swallowed melt spherules if they had been in the river channel.

Looking at the fish in a different way.

In December 2021, DePalma and his colleagues published a paper about the timing of the extinction event. The study looked at how the cycle of seasons from summer to winter were documented in the structure and chemistry of the fish bones.

They found that the fish died when it was seven years old, when compared to the fossils from Tanis. The growth rings show the fish in fresh waters in the summer and saltwater in the winter. The last growth increment matches the transition from spring to summer in this specimen.

It is believed that the meteorite struck in May or June in the northern hemisphere.

The extinction event was thought to have taken place in early June.

Jack Wolfe, a paleobotanist, identified a location in Wyoming that showed the effect of the meteorite on a freshwater lake. The lake froze at the point of impact.

He showed that the latest water lilies in the lake had stopped producing leaves, flowers and fruit in early June because of the cold weather.

The month the dinosaurs died out is one of the details that paleontologists would need a time machine to understand. There are extraordinary conclusions that can be found from careful analysis and comparison with the modern day.

Journal information: Nature

This article is free to use under a Creative Commons license. The original article is worth a read.

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