While dinosaurs walked the Earth, a shark-like marine reptile swam the prehistoric oceans.
Ichthyosaurs, or “fish lizards,” were a carnivorous group of dolphin-looking creatures that ranged in size from seven to 30 feet long. Though they appeared earlier than the dinosaurs, around 250 million years ago, they disappeared tens of millions of years before the well-known end-Cretaceous extinction.
Now, an international team of scientists believe they know why ichthyosaurs disappeared so early. Their extinction, according to research published in Nature Communications, can be attributed to a combination of slow evolution and environmental volatility.
“Our results support a growing body of evidence revealing that rising sea levels and sea temperatures profoundly reorganized marine ecosystems about 100 million years ago,” said the study’s lead researcher Valentin Fischer to BBC News. “The ichthyosaurs were unable to adapt. They were evolving very slowly during the last 50 million years of their reign.”
Previous hypotheses pointed to a potential decline in ichthyosaurs’ food source, or competition from other marine species as a source for their extinction. However, the researchers believe a combination of factors led to their demise.
“Although the rising temperatures and sea levels evidenced in rock records throughout the world may not directly have affected ichthyosaurs, related factors such as changes in food availability, migratory routes, competitors and birthing places are all potential drivers, probably occurring in conjunction to drive ichthyosaurs to extinction,” Fischer said in a statement.
Fischer said ichthyosaurs were diversified in the time before their extinction. Several species existed with various body types and ecological niches.
According to the Univ. of Oxford, the new study supports the notion that a major reorganization of marine ecosystems occurred at the start of the Late Cretaceous. While ichthyosaurs faced extinction, other marine animals like bony fish and sharks evolved and persisted.
The researchers are currently investigating whether ichthyosaurs’ extinction was part of a larger event during this time period.