Featured Image: Brian Skerry
By:Jessica Kittel
If you have ever been whale-watching and have been lucky enough to catch sight of one roaming the seas, it’s hard not to appreciate just how huge whales really are.
Peering into the waters, the upcoming shadow gets larger and larger until you spot the 45-foot long humpback whale stretching longer than the width of the boat! And consider this: The blue whale is more than twice the size of the humpback whale.
Image Credit: Encyclopædia Britannica, Inc.
We assume that whales have always been this awe-inspiringly large, but that is actually not the case. While the exact date and time might evade us, researchers have managed to pinpoint a general time period, when whales graduated from mediocre to massive.
The ancestors of today’s modern whales made the transition from land back to the sea, roughly 55 million years ago. These ancestors are not what you would expect, based on the appearance of today’s modern whale.
These ancestors looked more like a deer-cat-hyena (they were, in fact, in the ungulate family). According to Scientific American, they were also exceptionally small, at about the size of a mouse deer.
Image Credit: Nobu Tamura
After adapting to their new oceanic environment, whales transitioned from a deer-cat-hyena appearance to one that more closely resembles what we would recognize today as a whale.
Two main guilds arose. One guild included large, herbivorous marine mammals. Think: sea grass munching sea cows and their relatives.The other, included filter-feeding mysticete whales (baleen whales such as the humpback).
Paleontologists Nicholas Pyeson and Geerat Vermeij believe it was the different menus between the two guilds that led to the current size disparage between the two.
According to Smithsonian Magazine, while the herbivorous marine mammals reached their maximum size range around 30 million years ago, the mysticetes didn’t start to grow until around 5.3 million years ago. It wasn’t until around 2.5 million years ago, during the onset of the Pleistocene, that the mysticetes reached their current gargantuan sizes.
Mysticete whales possibly adapted filter-feeding as early as the Oligocene period (33.9 to 23 million years ago). This technique allows them to survive on some surprisingly small creatures, namely krill.
Image Credit: Animal Picture Society
So, despite their large size, they are dependent on food that is very closely associated with primary production. Not surprisingly, it was an influx in ocean productivity during the Pleistocene period that finally allowed these filter-feeding whales to reach their massive sizes.
However, it wasn’t overall ocean productivity, but the distribution of this productivity that researchers believe had the largest impact.
We can thank the Ice age for our large ocean friends. Giant ice sheets and glaciers all over the globe would scrape against rocky substrate, releasing nutrient rich bits of rock into the sea. These nutrients, in turn, spurred an increase in primary production and shish-boom-bang, big whales.
In reality, it probably wasn’t quite that simple. Researchers have found multiple periods of increased primary production that pre-dated this particular one. However, those didn’t result in such an extreme increase in size.
Smithsonian Magazine suggests that what made this situation unique was the way the productivity was distributed around the globe. The primary productivity was likely patchy and spread around different parts of the globe so, while there was plenty to eat, you had to get from one spot to another before you could have your next meal.
This set-up favored creatures that could store enough energy to get from one spot to the next and could travel quickly. Larger body sizes not only allowed for more storage space, but could also push through water more efficiently.
Cheers to our massive friends! That is quite the transformation.
Read more from our sources Scientific American and Smithsonian Magazine.