Two groups of tiny, delicate marine organisms, sea butterflies and sea angels, were found to be surprisingly resilient—having survived dramatic global climate change and Earth’s most recent mass extinction event 66 million years ago, according to research published this week in the Proceedings of the National Academy of Sciences led by Katja Peijnenburg from Naturalis Biodiversity Center in the Netherlands.
Sea butterflies and sea angels are pteropods, abundant, floating snails that spend their entire lives in the open ocean. A remarkable example of adaptation to life in the open ocean, these mesmerizing animals can have thin shells and a snail foot transformed into two wing-like structures that enable them to ‘fly’ through the water.
Sea butterflies have been a focus for global change research because they make their shells of aragonite, a form of calcium carbonate that is 50 percent more soluble than calcite, which other important open ocean organisms use to construct their shells. As their shells are susceptible to dissolving in more acidified ocean water, pteropods have been called “canaries in the coal mine,” or sentinel species that signal the impact of ocean acidification.
With some pteropods having thin shells and others having only partial or absent shells, such as the sea angels, their fossil record is patchy. Abundant pteropod fossils are only known from 56 million years ago onward and mostly represent the fully-shelled sea butterflies. These observations led to the notion that evolutionarily, pteropods are a relatively recent group of gastropods.
An international team of researchers sampled 21 pteropod species