First Giant Baleen Whale Hides In Southern Hemisphere

A fossil whale jaw found on the banks of Australias Murray River is larger than previously thought possible for such an ancient fossil. Along with other surprisingly large southern fossil whales, the find suggests that whales began to flourish in the Southern Hemisphere long before they flourished in the North.

It also suggests baleen whales, a group including the largest animals of all time, are much older than previously suspected. The reason their presence was not recognized earlier is a problem that causes many areas of science: Northern Hemisphere bias.

Blue whales can reach 30 meters (98 feet) in length, but this is thought to be a recent development in evolutionary time. The rise of large baleen whales, which feed on large catches of krill rather than hunting individual fish or mammals like their toothed counterparts, is dated to about 19 million years ago.

Dr James Rule and Dr Erich Fitzgerald with two living pieces of a 19 million year old whale jaw, revealed some whales of those times that were larger than previously known.

Image credit: Eugene Hyland, Museums Victoria

Monash University’s Dr James Rule told IFLScience that an apparently plausible story was once accepted about baleen whales increasing in size.

The time when the first truly large whales in the Northern Hemisphere were found coincides with the beginning of the Ice Age. This is also about the time when the megalodon disappeared, possibly making the oceans safer for large animals. It also coincided with the disappearance of other whale families.

All this creates a neat picture that palaeontologists in the Northern Hemisphere love where baleen whales seize a new niche and continue to grow, rapidly increasing their current large size.

comparing the size of a fin whale, Murray whale and a diver

Compared to modern fin whales, the Murray River whale doesn’t look very impressive, but you have to start somewhere.

Image credit: Art by Ruairidh Duncan, graphic by Rob French, Museums Victoria

Those responsible for this story do not have one thing that most of the world’s oceans are in the Southern Hemisphere, including the incredibly productive waters of the Antarctic Circumpolar Current.

Back in 1921, the front of the lower jaw was found on the banks of the Murray River and brought to Museums Victoria. There, it was neglected for nearly a century until the appointment of Dr Erich Fitzgerald, a cetacean specialist who began surveying the museum’s archives for anything whale-related. Fitzgerald suspected the fossil might be important, and Rule suggested it when he was looking for a student project.

Rule and Fitzgerald found that the tips of baleen whales jaws are in proportion to their body length. Based on this, they calculated the specimen from a 9-meter (30 foot) whale.

By modern standards that is modest, but it crushes the 5-meter ceiling that is believed to have existed 19 million years ago when the sediments in which the bone was found were laid down.

This was a time when the Southern Ocean was just beginning to form and modernize, Rule told IFLScience. the [larger] the whales probably found there was plenty of food there and didn’t need to go anywhere else.

Although large whales may not have crossed the equator, this individual was farther from the krill-rich waters of Antarctica Australia than it was further south, but not by that much.

Higher seas at the time flooded much of what is now South Australia and the whale would have been swimming in a shallow offshore sea when it died. The water is unusually shallow for a whale of this size, Rule said, but with just one specimen, the team can’t tell if the whale is lost, permanently resident in the area, or migrated to warmer waters to breed, like many modern whales. do it.

Whales in the northern hemisphere are thought to have experienced a long period of size stability, followed by rapid growth.  This probably happened when whales in the southern hemisphere crossed the equator

Whales in the Northern Hemisphere are thought to have experienced a long period of size stability, followed by rapid growth. This probably happened when the whales of the Southern Hemisphere crossed the equator.

Image credit: Art by Ruairidh Duncan, Museums Victoria

Fossil hunting in Antarctica has obvious difficulties, so we probably don’t know much about these early giants in what might have been their territory. However, Rule told IFLScience that discoveries from South Africa, Peru, and New Zealand suggest a much slower expansion of the baleen whale’s range than previously thought across the Southern Hemisphere. When planetary conditions made the north another suitable habitat, some migrated there, creating the impression of a sudden explosion in size.

This is missing because only 19 percent of reported whale fossils come from north of the equator.

The Southern Hemisphere, and Australia in particular, are often overlooked frontiers for fossil whale discoveries, Fitzgerald said in a statement.

Noting that without Fitzgeralds appointment, the important piece of the jaw would still be ignored, Rule told IFLScience; It’s always good to have more scientists. If there are more scientists there will be more science done.

The study was published in the Proceedings of the Royal Society B.

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