Baleen whales (mysticetes) include the largest animals on the Earth. How they achieved such gigantic sizes remains debated, with previous research focusing primarily on when they became large, rather than where. Now, paleontologists have described an edentulous baleen whale (chaeomysticete) fossil from South Australia. With an estimated body length of 9 m, it is the largest baleen whale from the Early Miocene. Analysing body size through time shows that ancient baleen whales from the southern hemisphere were larger than their northern counterparts.
Until now, it was believed that the beginning of the Ice Age in the northern hemisphere about 3 million years ago kickstarted the evolution of truly gigantic baleen whales.
The new study, led by Dr. James Rule from Monash University and Natural History Museum, London, reveals that in fact this evolutionary leap in size happened as early as 20 million years ago and at the polar opposite, in the southern hemisphere.
The major discovery came from research into a 16 to 21-million-year-old fossil cared for in the Museums Victoria collection.
The specimen — the front end of the lower jaw of a large edentulous baleen whale — was recovered from a cliff face on the bank of the Murray River in South Australia in 1921 but was largely unrecognized in the collection.
In their study, Dr. Rule and colleagues show how whales evolved into gigantic sizes first in the southern hemisphere, not the northern, and have had larger body sizes in the south for their entire evolutionary history — some 20–30 million years.
The findings underscore the vital importance of the Australian and wider southern hemisphere fossil record for piecing together the global picture of whale evolution.
The previous ruling hypothesis was based on fossils primarily found in the northern hemisphere, but the Murray River whale fossil disrupts that theory.
“The southern hemisphere, and Australia in particular, have always been over-looked frontiers for…
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