Illustration by Jaime Bran for Te Papa Museum.
The discovery of an extinct species of monk seal, which lived 3 million years ago, overturns what we previously knew about how seals evolved.
James Rule at Monash University in Melbourne, Australia, and his colleagues identified the new species while examining fossil specimens that had been found on beaches in South Taranaki, on the west coast of New Zealand’s North Island.
It has been named Eomonachus belegaerensis, after the fictional Belegaer sea from J.R.R. Tolkien’s Lord of the Rings.
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Seven fossils, including a complete skull, were found between 2009 and 2016 by members of the public. They are the oldest evidence of monk seals ever discovered. The fossils suggest that this species was approximately 2.5 metres long when fully grown, and weighed 200 to 250 kilograms.
Based on its teeth, the seal’s diet was probably similar to that of living monk seals, consisting of fish, squid and octopus, says Rule.
The discovery overturns accepted knowledge about how true seals – which are earless and a distinct group from fur seals and sea lions – evolved.
“It was previously thought that all [true] seals, including monk seals and the Antarctic seals, originated in the North Atlantic Ocean,” says Rule. “That’s where most of the fossils of seals have been found.”
Scientists had believed that these seals then crossed the equator to populate the southern hemisphere. But the discovery of E. belegaerensis in New Zealand suggests that the ancestors of living Antarctic, elephant and monk seals actually evolved in the southern hemisphere.
The researchers incorporated the new discovery into an analysis of the distribution of living and extinct seals globally over time. They concluded that many seals may have instead evolved in the southern Pacific and crossed the equator up to eight times.
“It seems to imply that true seals have broad environmental tolerances,” says Rule. “This actually makes sense when you look at the distribution of true seals today.”
Living monk seals are found in tropical and sub-tropical waters, while all other species of true seals are found in polar regions.
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2020.2318
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