Early giant baleen whales hidden in southern hemisphere

A fossilized whale jaw found on the banks of Australia’s Murray River is much larger than was thought for such an ancient fossil. Along with other surprisingly large southern whale fossils, the discovery suggests whales began growing in the Southern Hemisphere as early as the Northern Hemisphere.

It also shows that baleen whales, a group that includes the largest animals ever to exist, are much older than previously thought. The reason their existence went unrecognized early on is a problem that plagues many fields of science: Northern Hemisphere bias.

Blue whales can reach 30 meters (98 feet) long, but this is considered a relatively recent development in evolutionary history. The rise of giant baleen whales dates back to about 19 million years ago, and they feed on large amounts of harvested krill, rather than individual fish or mammals like toothed whales.

Dr James Ruhl of Monash University told IFLScience that a plausible story about baleen whales growing up had previously been accepted.

The discovery of the first truly large Northern Hemisphere whales coincided with the beginning of the Ice Age. This is also the time when the megalodon disappeared, which may have made the oceans safer for the large animals. This also coincided with the disappearance of several other families of whales.

It all creates a clear picture favored by northern hemisphere paleontologists, in which baleen whales seized on new ecological niches and grew, rapidly evolving to their current gigantic size.

Those responsible for this story are missing just one thing: Most of the world’s oceans are in the Southern Hemisphere, including the unusually rich waters of the Antarctic Circumpolar Current.

As early as 1921, the front part of a lower jaw was discovered on the banks of the Murray River and brought to Museums Victoria. There it lay neglected for nearly a century, until the appointment of cetacean expert Dr. Erich Fitzgerald to investigate whether there was anything related to the whale in the museum’s archives. Fitzgerald suspected the fossil might be important and suggested it to Ruhl when he was looking for a student project.

Rule and Fitzgerald found that the tip of a baleen whale’s jaw is proportional to its body length. From this, they calculated that the specimen came from a 9-meter (30-foot) whale.

That’s not high by modern standards, but it breaks the 5-meter upper limit that existed when the sediments where the bones were found were deposited 19 million years ago.

Ruhl told IFLScience that the Southern Ocean was just beginning to form and modernize.this [larger] The whales may find there is more food there and don’t need to go elsewhere.

While the Great Whale may not have crossed the equator, this whale was far from Antarctica’s most krill-rich waters, and Australia was further south at the time, but not that far.

High seas at the time had submerged much of what is now South Australia, and the whale may have been swimming in shallow water when it died. Ruhl said the waters were unusually shallow for a whale of its size, but with just one specimen, the team couldn’t tell whether the whale was lost, living in the area permanently or migrating to warmer climates like many modern whales. Breeding in water. Do.

There are obvious difficulties in finding fossils in Antarctica, so we may never learn much about the homeland of these early giants. However, Ruhl told IFLScience that findings from South Africa, Peru and New Zealand suggest that the size expansion of baleen whales throughout the Southern Hemisphere is much slower than thought. Once planetary conditions make the north a suitable alternative home, some will migrate there, giving the impression of a sudden explosion of scale.

The discovery was overlooked because only 19% of reported whale fossils come from north of the equator.

Fitzgerald said in a statement that the Southern Hemisphere, and Australia in particular, has been a neglected frontier in whale fossil discovery.

Rule told IFLScience that without Fitzgerald’s appointment, important parts of the jaw would still have been neglected. It’s always good to have more scientists. If there are more scientists, there will be more scientific results.

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