Dinosaurs became extinct in the spring: “Was at a sensitive time” | Science

Paleontologists agree that a meteor impact on Mexico’s present-day Yucatán Peninsula some 66 million years ago marked the end of the flightless dinosaurs. This is also known as the fifth mass extinction.

“That impact shook the continental plate and created large waves in rivers and other water bodies. That released enormous amounts of sediment that fishes buried alive,” says Melanie During of VU Amsterdam and Uppsala University. “Meanwhile, it rained small glassy spheres: molten pebbles that had ejected from the impact crater, vitrified into the air and landed a few thousand kilometers away.”

_{Read more below the video.}

The researchers found these spheres in the gills of some fossil sturgeons at the American site Tanis, in North Dakota. That’s immediate evidence of their deaths shortly after the meteor impact. “They were very clearly visible on X-ray scans,” says VUB researcher Koen Stein. The scans also showed the scientists in which season the fish died: “We studied the internal bone structure of six fossil sturgeons. You can read the seasonal growth from this, just like with trees. These fish died when it was spring in the Northern Hemisphere.”

_{Read more below the photo.}

The bone cells of the fish also confirm this theory: their size and density also change under the influence of the seasons. “In all fish fossils, we were able to analyze bone cell density and size over several years. In the year of the meteor impact, they were growing, but had not yet reached their peak,” said Dennis Voeten of Uppsala University.

“We can really conclude from this that ‘the great death’ came in the spring,” says During. “That was at a sensitive time, because in the spring the reproductive cycle starts for many animals. The incubation period in reptiles such as dinosaurs and pterosaurs is also longer than in other groups of animals, such as birds, so they may have been more sensitive to the sudden disturbance of their environment.”

_{Read more below the photo.}

It also explains why some animal species survived the devastating meteor impact. In the southern hemisphere it was autumn: “Animals that had already started their hibernation underground at that time, including some early mammals, can thus have survived the first months after the meteor impact, with large-scale forest fires,” says During.

Argentine scientists discover new ‘armless’ dinosaur species

Scientists discover that dinosaurs also suffered from respiratory infections