Ancient otter-like seal’s brain reveals it may have foraged with its whiskers

Brain cavity scans of a 23-million-year-old relative of today’s seals reveals that the creature likely used its whiskers to forage in ancient waters. The findings shed further light on how ancient seals transitioned from life on land to the water.

Potamotherium valletoni is known from thousands of fossils. The genus Potamotherium (meaning “river beast”) was first described in 1833.

The ancient pinniped (the family of mammals which includes seals) would have resembled an otter and lived during the late Oligocene (34–23 million years ago) and Miocene (23–5.3 million years ago) in Europe and North America.

During this period, Europe was warmer and wetter than today. Much of the continent was under water and the Paratethys sea stretched from the region north of the Alps over central Europe to Central Asia. As the climate dried during the Miocene, the sea levels dropped, and open grassland and savannah began to form in parts of Africa and Asia.

Researchers led by Dr Alexandra van der Geer from Leiden University in the Netherlands published a paper analysing Potamotherium brain cavities in Communications Biology.

The team compared the brain structure of Potamotherium with those of six extinct and 31 living meat-eating mammals.

Potamotherium’s coronal gyrus – a region of the brain linked to sensory information such as pressure, pain, and warmth – is larger than those of ancient and living land-based mammals that use their forelimbs to forage. It is smaller, however, than ancient seal relatives and semiaquatic mammals, such as the Eurasian otter, that predominantly use their whiskers to explore underwater.

The findings suggest that Potamotherium used its whiskers and forelimbs together when foraging.

Such a transition from foraging with the forelimbs to using tactile sensations from the whiskers may have been critical in the move of ancient pinnipeds from land-based creatures into the water, the authors argue.

“We postulate that the increased tactile performance of mystacial vibrissae [facial whiskers] of modern pinnipeds was already present around the beginning of the transition from a terrestrial to an aquatic lifestyle and facilitated their transition to an amphibious lifestyle,” they write.

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