How pygmy whales were affected by historical climate change

In one of the latest posts here, we described to you a new discovery of giant ancient killer whales dominating the ancient seas that used to cover Egypt. Now, we are staying along the same taxonomic theme to being you a story of pygmy whales!

An article, published back in 2017, shows how fossils whales moved around the seas during intense glacial and interglacial periods. Importantly, it provides a strong case of how physical barriers can play a major role in the evolution of marine mammals – something we should be very much aware of as we continue to impact upon global climates.

The modern pygmy right whale, Caperea marginata, is known exclusively from the southern hemisphere – places such as southern Australia, New Zealand, and South America. It is well known as being the smallest of its kind, and due to some of its weird anatomy some times even called the ‘platypus of whales’. Fossils of this baleen whale lineage are also exceedingly rare, and only ever found on the southern continents.

Now, researchers have found fossils of this species, but as far north of the equator as Japan and Italy. The ones from Japan, consisting part of a skull, are between 0.5-0.9 million years in age. The Italian fossil comprises just a single ear bone, and is older at between 1.7-1.9 million years old. However, just from these elements it is possible to identify them as the same species as the modern pygmy whale, or at least a very, very close ancestor. This is the first time these animals have been found so far north, and prove quite an unexpected discovery.

“This is like finding a fossil kangaroo in Scotland. It us a totally unexpected discovery,” said Erich Fitzgerald, Senior Curator of Vertebrate Palaeontology, Museums Victoria, where the fossils are housed.

Whales and global climate change

But perhaps most importantly, these whale fossils help to illuminate a whole new element of the environmental history during the Quaternary period. It means that climates that we now associate with the southern hemisphere were once common in the northern hemisphere too, which impacted the distributions of marine mammals at the time.

It is not uncommon for whales to migrate seasonally, but at this scale helps to tell us more about the environment at the time. During the Pleistocene period, when the fossils are known from, the Earth was still very different to how we know it today. Great ice sheets expanded and contracted across both hemispheres. These would force marine animals to migrate and shift their habitats north and south as the glaciers grew and declined.

Finding the pygmy whales so far north then suggests that they lived during a time when the southern ice caps had grown far north towards the equator, and perhaps even further. As the climate warmed again over many millennia, the ice caps retreated and the whales were able to slowly shift to their more southerly waters again. Fossils of this, and related, species are unknown from all other well-sampled fossil localities from around the same time in the northern hemisphere.

Where are the Japanese and Italian pygmy whales today?

But why are there no pygmy whales left in the North? Well, this is where the story gets a bit sad. As the climate continued to warm, it would make the equatorial waters more and more difficult to cross. So those pygmy whales left in the north would find it more difficult to migrate, become increasingly isolated, and eventually die out. Due to the time differences between the two fossils, however, it is difficult to say whether there was one longer lasting population or two population pulses of pygmy whales during this period.

Dr Felix Marx, Research Associate at Museums Victoria and Monash University, added that this points to the potential huge impact of ongoing climate change on today’s whales: “The natural changes to the Earth’s climate, now has an added human element, that may drive a reorganization of the current dispersal of whales and marine mammals. For example, a warmer world may see the pygmy right whales driven further south towards the pole.”

In the future, this means that we might also expect to find fossils of other ‘southern’ animals in the northern hemisphere, such as penguins and even walruses. Discovering more fossils from this time will be important in helping to understand how these species might respond to future changes to our global climate.

Reference

Tsai, C.H., Collareta, A., Fitzgerald, E.M., Marx, F.G., Kohno, N., Bosselaers, M., Insacco, G., Reitano, A., Catanzariti, R., Oishi, M. and Bianucci, G., 2017. Northern pygmy right whales highlight Quaternary marine mammal interchange. Current Biology, 27(19), pp.R1058-R1059. LINK