Emily Chan
For a time, walruses thrived, but around three million years ago, everything changed. The Isthmus of Panama formed between North and South America, closing off the seaway.
Global cooling started during the Late Pliocene, causing sea levels to drop as the water froze to become polar ice caps.
Marine life was significantly impacted, and most of the world’s walruses died out, including O. posti. They became extinct during the Early Pleistocene around 1.7 million years ago, giving rise to the cold-adapted modern walrus.
“Walruses like Ontocetus depend on shallow water to find food in, so as sea levels fell, these habitats would have slowly disappeared,” said Dr. James Rule, an expert on seals and their relatives at the Natural History Museum.
“The wider climate changes are also thought to have affected mollusk populations, leaving these specialists with less and less to eat.”
Currently, O. rosmarus is the only living member of its family. Although O. rosmarus and O. posti are separated by millions of years, they share similar characteristics and lifestyles.
Overall, the discovery highlights how changes in the environment shape the survival of walrus species.
