A new study of marine life and fossils from Antarctica, Australia, New Zealand and South America reveals that one of the greatest changes to the evolution of life in our oceans occurred more recently than previously thought.
The Marine Mesozoic Revolution (MMR) is a key theory in evolutionary history. During the Mesozoic period, marine predators evolved so that they could drill holes and crush the shells of their prey. Although small in comparison to dinosaurs, these new predators, including crustacea and some types of modern fish, had a dramatic impact on marine life.
Among the species most heavily affected were sea lilies or isocrinids, this is because sea lilies are related to:
- Sea urchins; and
- Sand dollars.
At their height, forests of sea lilies carpeted seafloors all over the world.
Their restricted ability to move made sea lilies vulnerable to the new predators, so during the MMR they were forced into deeper waters to survive. Since it marked such a radical change in marine communities, scientists have long sought to understand this shift. They believed it occurred around 66 million years ago, but this new study shows that in the Southern Hemisphere sea lilies remained in shallow waters until much more recently – around 33 million years ago.
Evidence for the shift in marine life
A team from the British Antarctic Survey (BAS), the University of Cambridge, the University of Western Australia, and the Royal Botanic Gardens, Victoria, UK, made the discovery when they brought together field samples from Antarctica and Australia, with fossils from museum collections for the first time.
The study provides evidence that this change happened at different times in different parts of the globe, and that in the Antarctic and Australia sea lilies hung on in shallow waters until the end of the Eocene, around 33 million years ago. Though it is unknown exactly why.
The study shows that knowing more about the Antarctic can reshape – or overturn – existing scientific theories.
According to lead author Dr Rowan Whittle from the British Antarctic Survey: “It is surprising to see such a difference in what was happening at either end of the world. In the Northern Hemisphere these changes happened whilst the dinosaurs ruled the land, but by the time these sea lilies moved into the deep ocean in the Southern Hemisphere, the dinosaurs had been extinct for over 30 million years.
“Given how the ocean is changing and projected to change in the future, it is vital that we understand how different parts of the world could be affected in different ways and at a range of timescales.”