The discovery of an ancient fossil points to a grim future for modern seals

By Angela Heathcote 14 April 2020
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The fossilised tooth of an ancient seal is an exciting discovery, but scientists say it may indicate a bleak future for our sea lions and fur seals.

THE DISCOVERY OF a rare, three-million-year-old fossil has revealed an ancient group of seals once ruled Australia’s coastlines, but also hints at a dangerous future for living seals under global heating. 

The fossilised tooth, found along Portland Beach in south-western Victoria in 1998, was recently analysed by Monash University paleontologist James Rule, who found it belonged to an ancient group of seals known as ‘true’ seals, more commonly known as earless seals.

The tooth is one of only two known earless seal fossils to be discovered in Australia. The other fossil, found in the 1980s, revealed that the ancient seals had lived along Australia’s coastlines as far back as six million years ago. 

The ancient earless seal differs greatly from modern sea lions and fur seals that occupy Australia’s coastlines today. They are more similar to the tropical monk and Antarctic leopard seals that belong to the southern group of earless seals.

“Earless seals don’t have the ability to walk on land,” James says. “When they’re on beaches they have to wriggle or bounce, which differs from sea lions and fur seals that can still walk on land and have external ears.”

Related: Fighting for Australia’s precious sea pups

According to James, learning exactly how these ancient seals became extinct could shed light on what may happen to Australia’s modern seals under a rapidly heating world.

The ancient earless seal’s extinction coincides with a change in the climate that occurred 2.5 million years ago, when the earth began to cool and the Ice Ages began. The Poles became icier and the sea levels dropped.

The warmer climate, sandy beaches and shallow coastal environments that the earless seals thrived in began to disappear and eventually, so did the seals. “It would have eliminated the environments the seals used to swim in and the beaches they rested on,” James says.

The rocky beaches and islands created by this new climate eventually enticed Australia’s modern fur seals and sea lions, which began dispersing from their North Pacific home around 2 million years ago, slowly making their way to the South Pacific. The oldest-known sea lion fossil in Australia only dates back 500,000 years, making them relative newcomers. 

Related: A guide to Australia’s seals and sea lions

However, the rocky beaches and islands Australia’s sea lions and fur seals enjoy are quickly disappearing. 

“As the Earth continues to warm, ice melts and sea levels continue to rise. It’s most likely going to eliminate the environments that our seals use to rest, breed and hunt in,” James says, and as these environments disappear, so will the seals.

James is determined to pull together more pieces of this puzzle and gain a better understanding of what the future holds for Australia’s beloved fur seals and sea lions.

“We need to go out there and find more fossils. The more fossils we have, the more we’ll know about the earless seals’ past and how they went extinct.

“The seals of the past will be critical to informing us about the seals of today in the onset of the changing climate.”