3-Million-Year-Old Fossil from New Zealand Rewrites Evolutionary History of True Seals
Living true seals are the most widely dispersed semi-aquatic marine mammals, and comprise geographically separate northern and southern groups. Both are thought to have evolved in the North Atlantic, with only two lineages subsequently crossing the equator. The third and oldest lineage, the monk seals, has been interpreted as exclusively northern and subtropical throughout their entire history. However, an international team of paleontologists now describes a new species of extinct monk seal that lived during the Pliocene epoch in New Zealand — the first of its kind from the southern hemisphere.
The newly-identified monk seal species lived in the waters around New Zealand some 3 million years ago.
Named Eomonachus belegaerensis, the marine creature was around 2.5 m (8.2 feet) in length and has a mass between 200 and 250 kg.
“This new species of extinct monk seal is the first of its kind from the southern hemisphere. Its discovery really turns seal evolution on its head,” said lead author James Rule, a Ph.D. candidate in the Biomedicine Discovery Institute at Monash University and Museums Victoria.
“Until now, we thought that all true seals originated in the northern hemisphere, and then crossed the equator just once or twice during their entire evolutionary history.”
“Instead, many of them appear to have evolved in the southern Pacific, and then criss-crossed the equator up to eight times.”
Rule and his colleagues from New Zealand, Australia and the United States examined seven well-preserved specimens of Eomonachus belegaerensis — including a complete skull — found by local fossil hunters on south Taranaki beaches in New Zealand between 2009 and 2016.
“This discovery was a triumph for citizen science,” said co-author Dr. Felix Marx, a curator of marine mammals at the Museum of New Zealand Te Papa Tongarewa and a researcher in the Department of Geology at the University of Otago.
“This new species has been discovered thanks to numerous, exceptionally well-preserved fossils — all of which were found by members of the public.”
“Our results suggest that true seals crossed the equator over eight times in their history,” the paleontologists concluded.
“Overall, they more than double the age of the north-south dichotomy characterizing living true seals and confirms a surprisingly recent major change in southern true seal diversity.”
The discovery is reported in a paper in the Proceedings of the Royal Society B: Biological Sciences.
James P. Rule et al. 2020. First monk seal from the Southern Hemisphere rewrites the evolutionary history of true seals. Proc. R. Soc. B 287 (1938): 20202318; doi: 10.1098/rspb.2020.2318