The meteorite that killed the dinosaurs appears to have killed a fairly famous organism

The impact of space rocks not only led to the extinction of the dinosaurs, but also led to the end of the ammonites.

When you think of fossils, you probably quickly think of ammonites. Recognizable by their distinctive spiral shells, these sea creatures are one of paleontology’s most iconic icons. They flourished in Earth’s oceans for more than 350 million years until they suddenly became extinct at the end of the Cretaceous period. Researchers now believe they know better what led to their deaths.

no escape?
Some paleontologists have argued that the demise of the ammonites was inevitable. For example, the diversity of ammonites may have declined long before their extinction at the end of the Cretaceous. Recent research published in Nature CommunicationsHowever, it suggests otherwise. While it was previously thought that ammonites were in a long-term decline before becoming extinct, this research shows that the survival of these marine animals has come to an abrupt end.

meteor
According to the researchers, ammonites also suffered from the catastrophic meteorite impact that killed the dinosaurs. The impact caused climate changes, such as cooling due to dust and soot in the atmosphere and possibly also short-term warming due to greenhouse gases such as carbon dioxide released during the impact. Additionally, the impact likely caused tsunamis and wildfires, which contributed to the disruption of marine and rural ecosystems. These sudden changes in the environment had far-reaching consequences for many plant and animal species, including ammonites. Although ammonites have long thrived in the oceans, they were unable to withstand the sudden and drastic changes that occurred as a result of the meteorite impact.

Database
In short, ammonites became extinct due to the same accidental event that wiped out the dinosaurs 66 million years ago. The researchers reached this conclusion using an extensive database of Late Cretaceous ammonite fossils. According to the researchers, this comprehensive database is very important. “It is very difficult to understand how and why biodiversity has changed over time,” explains lead author Joseph Flannery Sutherland. “The fossil record tells part of the story, but it often cannot be relied upon as the sole source. In particular, patterns of diversity can show where and when new fossil species were discovered. But they often do not provide a good picture of actual biological history.”

Gaps
So the researchers assembled a new database of ammonite fossils from the Late Cretaceous to fill gaps in their data. “This way we can ensure we get a more detailed picture of biodiversity before they become completely extinct,” said co-author Cameron Crossan.

Species and extinctions
Using this database, the team analyzed how the rates of new species creation and extinction of ammonites varied across different parts of the world. What they found was that the balance between these processes varied not only across geological time, but also between different geographic regions. “The differences in how ammonites diversified across different parts of the world are key to understanding why their history in the Late Cretaceous has been misinterpreted,” says researcher James Witts. “In North America, the ammonite fossil record is widely documented. If you looked at that alone, you might think they were already dying out, when in fact they were thriving elsewhere. Their extinction was really a coincidence rather than an inevitable outcome.”

Factors
To find out why ammonites continued to be so successful during the Late Cretaceous, the team examined potential factors that influenced their diversity over time. They wanted to know whether ammonite reproduction and extinction rates were influenced mainly by environmental factors such as ocean temperature and sea level, or by biological factors such as predators and mutualistic competition. “Our findings show that the causes of the emergence and extinction of ammonite species were highly diverse across different geographic locations,” concluded co-author Corinne Myers. “You can’t simply look at the entire fossil record and conclude that their diversity was affected only by changes in temperature, for example. It’s much more complicated than that and depends on exactly where in the world they lived.

The study of the Late Cretaceous ammonite extinction provides important insights that challenge previous assumptions. “Paleontologists often prefer simple explanations for what caused changes in the fossil diversity of a group,” says researcher Flannery Sutherland. “But our research shows that the reality is not always that simple. We should not blindly rely on global fossil datasets, but rather analyse them at regional levels. This way we can gain a more detailed understanding of how biodiversity has evolved over time and space.”