The Murray River in Australia is home to a fossilized whale jaw that is significantly larger than was previously thought to be possible for such an old fossil. The discovery, along with other unexpectedly large southern fossil whales, indicates whales began to expand in the Southern Hemisphere much earlier than they did in the North.
It also implies that baleen whales—which include the biggest creatures on Earth—are far older than previously thought. Their presence was not recognized earlier due to a problem known as Northern Hemisphere bias, which plagues many scientific fields.
Although blue whales can grow up to 30 meters (98 feet) in length, this is believed to be a relatively recent evolutionary development. It has been estimated that the emergence of the massive baleen whales, which feed on enormous krill catches instead of hunting individual fish or mammals like their toothed counterparts, occurred approximately 19 million years ago.
Infoblendr was informed by Dr. James Rule of Monash University that a previously accepted narrative regarding the growth in size of baleen whales appeared to be plausible.
The beginning of the Ice Age was when the first really large whales from the Northern Hemisphere were discovered. Additionally, it coincides with the disappearance of the megalodon, which may have made the oceans a little safer for larger animals. Additionally, some other whale families’ disappearances coincide with it.
All of this painted a charming picture that paleontologists from the Northern Hemisphere adored, one in which baleen whales seized the new niche and simply kept growing, evolving quickly to reach their current enormous size.
The author(s) of this story omitted one important detail: the majority of the world’s oceans, including the incredibly productive Antarctic Circumpolar Current, are located in the Southern Hemisphere.
A lower jaw’s front was discovered on the Murray River’s banks in 1921 and brought to Museums Victoria. It was left undisturbed for nearly a century until Dr. Erich Fitzgerald, a specialist in cetaceans, was brought on board to search the museum’s archives for anything about whales. When Rule was looking for a student project, Fitzgerald suggested the fossil to him because he thought it might be important.
Rule and Fitzgerald discovered that the length of the baleen whales’ bodies corresponds to the tips of their jaws. They deduced from this that the specimen belonged to a whale that measured nine meters (30 feet).
While that may seem low by today’s standards, it shatter the 5-meter ceiling that was believed to exist when the sediments containing the bone were laid down 19 million years ago.
According to Rule, Infoblendr, “This was the time when the Southern Ocean was just starting to form and modernize.” “It’s likely that the larger whales discovered there was more food there and didn’t need to go elsewhere.”
Big whales might not have crossed the equator, but this particular whale was far from the Antarctic’s richest krill waters; Australia was slightly further south at the time.
Much of what is now South Australia had been inundated by the higher seas during that time, so the whale would have been swimming in a shallow coastal sea at the time of its death. Rule noted that “the waters were unusually shallow for a whale of this size.” However, the team is unable to determine whether the whale was lost, had made a permanent home in the area, or had migrated, like many modern whales, to warmer waters to breed.
Given the obvious challenges associated with fossil hunting off Antarctica, we may never learn much about these ancient giants in what was likely their home range. The rule did, however, inform Infoblendr that research from Peru, New Zealand, and South Africa points to a far slower expansion in baleen whale size than has been thought to have occurred throughout the Southern Hemisphere. There appeared to be an explosion in size when some moved to the north due to favorable planetary conditions.
Just 19% of whale fossils that have been reported come from regions north of the equator, so this had gone unnoticed.
Fitzgerald said in a statement, “The Southern Hemisphere, and Australia in particular, have always been over-looked frontiers for fossil whale discovery.”
Rule told Infoblendr that “it’s always good to have more scientists,” pointing out that the crucial piece of jaw would still be sitting ignored absent Fitzgerald’s appointment. More science is produced in the presence of more scientists.