A fossil discovery in New Zealand has revealed a new species of seal that once called Australasia home. Eomonachus belegaerensis is the first monk seal, living or extinct, ever found in the Southern Hemisphere. Its presence in our region turns the evolution of southern seals on its head. Curator Vertebrates Felix Marx talks about what this discovery means.
Monk seals are some of the world’s rarest and most endangered marine mammals. Unlike their largely polar relatives, they prefer the balmy waters of the Mediterranean, Hawaii and – until their extinction there in the 1950 – the Caribbean.
Fewer than 2,100 individuals remain today, and conservationists are now scrambling to save what’s left of Earth’s only tropical seals.
The origin of monk seals has long remained a mystery. Fossils are few and far between, and their closest relatives – elephant and Antarctic seals – live far away in the Southern Ocean.
Until now, what little evidence we had suggested that all of these seals (collectively known as ‘monachines’) evolved in the North Atlantic Ocean, despite their rather disparate geographical distribution today.
The unexpected discovery of a monk seal from New Zealand by a trans-Tasman team from Te Papa and Canterbury Museum, as well as Australia’s Monash University and Museums Victoria, now turns this idea on its head.
A monk seal from Aotearoa
The new monk seal is known from several beautifully-preserved fossils from the coast of Taranaki on New Zealand’s North Island, within the rohe of Ngāti Ruanui and Ngāruahine.
They were found by local collectors and are now preserved here at Te Papa and also Canterbury Museum. Their discovery was a triumph for citizen science, and shows what can be achieved when scientists and members of the public work together.
After identifying the new fossils as monk seals by studying their detailed shape, we eventually described them as a new species: Eomonachus belegaerensis, named after the great sea Belegaer to the west of J.R.R. Tolkien’s Middle Earth (aka the Tasman Sea).
The discovery of such a ‘northerner’ in our region was unexpected, to say the least. What were (sub)tropical monk seals doing in frigid New Zealand three million years ago?
Well, in the past, the waters around Taranaki were a lot warmer than they are today, perhaps by as much as 4 degrees. Perfect monk seal territory, it seems.
Seal evolution revisited
The discovery of Eomonachus in ancient Aotearoa casts light on more than just the evolution of monk seals.
Our observations now suggest that all monachines originated in the Southern Hemisphere. Elephant and Antarctic seals then simply stayed here, while monk seals (and one species of elephant seal) later migrated to the North Atlantic and North Pacific.
This is the exact opposite of what scientists had thought so far, and implies that monachines crisscrossed the equator up to eight times throughout their evolutionary history. This may not sound like much, but is actually quite remarkable, as the warm waters of the tropics are often thought to be difficult for marine mammals to cross.
Jumping between hemispheres means that ancient monachines likely had broad environmental tolerances (unlike their distant cousins, the fur seals and sea lions) that enabled them to spread around the world.
Climate change and seal extinction
So why aren’t monk seals living around New Zealand now? About 2.5 million years ago, many large animals in the ocean went extinct as global temperatures plummeted towards the ‘ice ages’. This event likely spelt the end for our monk seals, leaving their northern relatives as the last vestiges of a once widespread lineage.
Extinction is part of the circle of life, and has shaped ecosystems for as long as they have existed. Yet Eomonachus also serves as a cautionary tale: just like natural climate change drove monk seals to extinction in the south, human actions and global warming today threaten the survival of their northern relatives.
Many more stories of life and death, evolution and extinction, are hidden in Aotearoa’s past. New Zealand rocks hold an abundance of ancient marine life, some of its stretching back to the time of the dinosaurs: from giant marine reptiles, penguins, and turtles to sharks, whales, dolphins, and seals. Much of its remains to be explored – so far, we have barely scratched the surface.
Parts of this blog have been adapted from an article published in The Conversation 11 November, 2020 by:
Palaeontology PhD Candidate Monash University
Curator Vertebrates Te Papa Tongarewa
Senior Curator Vertebrate Palaeontology from Museums Victoria
Senior Lecturer, Department of Anatomy and Developmental Biology Monash University