Unlocking whale size mystery: New study suggests climate change wasn't the sole driver

There's a common belief that the present size of whales is a consequence of climate change during the ice age. The prevailing theory among scientists is that smaller aquatic creatures were more challenged by colder waters than larger ones, leading over time to larger marine mammals. Nevertheless, this theory was developed with some data gaps, and is primarily dependent on prehistoric whale remains found in the northern hemisphere.

The latest research findings address data gaps that have puzzled scientists till now. Remarkable whale remains, approximately 19 million years old, were discovered onshore along the Murray River in South Australia back in 1921. Interestingly, the toothless animal was about 30 feet in length—that's comparable to today's dwarf fin whales. Yet, more than a century passed before these remains were completely scrutinized, and the results astonished scientists.

Initial comparison of the remains discovered off the Australian coast with those from the northern hemisphere revealed a striking evolutionary divergence among whales. Whales in the southern hemisphere were not progressively increasing in size. Instead, the researchers explain, "Southern species achieved relatively larger sizes at earlier stages, likely due to greater regional environmental productivity."

Simply put, southern hemisphere whales began to enlarge significantly earlier than their northern hemisphere kin. Growth of the latter potentially started with the advent of the Ice Age. "The initial large-bodied species coincided with Antarctica's glaciation and seasonally productive polar ecosystems around 36-33 million years ago", researchers add.

Shortly afterwards, around 23 million years ago, krill evolved. Krill comprises a significant aspect of the whale diet today. This, potentially, could have acted as yet another catalyst for whale size increase, providing improved living conditions.