Although scientists agree on most of the major extinction events in the Earth's history, there are a few select species whose disappearance is still a mystery. The ichthyosaur - a swimming, dolphin-like reptile that roamed the waters for more than 150 millions years - is one of these creatures. Now, a new study from researchers at the University of Oxford claims to have revealed more about their vanishing 65 million years ago, and they believe that a climactic change during the late Cretaceous period was the main cause.
The team sifted through museum collections and literature on ichthyosaur fossil findings in order to create the most comprehensive dataset of the many different species of ichthyosaur that existed over the animal's life on Earth. Afterwards, they investigated the links between each species and the nature of their evolution over time.
The resulting picture is a diverse group of organisms that maintained a great deal of species richness. However, that came to an end during two separate extinction events - one that greatly reduced their numbers during the late Cretaceous period, and another several million years later that completely wiped them out.
The team performed mathematical analyses to determine the environmental changes that would best predict the ichthyosaurs' demise and found that in the late Cretaceous period, climate changes were the biggest predictors. This fits with current fossil findings and geological evidence that points to a massive environmental upheaval around the time that they first started to decline. Inconsistent temperatures and sea levels, as well as changes in the amount of oxygen and carbon dioxide in the ocean, were the biggest characteristics of this upheaval.
"Although many authors have speculated on the causes of the extinction of the ichthyosaurs, this new study presents the most thorough data set to date," said Erin Maxwell, who conducted previous research that suggested ichthyosaurs died out due to direct competition with other marine reptiles.
Maxwell added: "The finding that climatic instability is an important driver of extinction dynamics in these large reptiles is consistent with our understanding of extinction processes - namely that rapid climate change is an ecological stressor that can result in extinctions in all levels of the food chain, but especially among top predators."
The findings were published in the Mar. 8 issue of Nature Communications.
