New fossil gives insight into feeding habits of ancient orcas

New research by scientists suggests that orcas and false killer whales only evolved to feed on marine mammals within the last one million years.

The two species are the only members of the 90 or so species of cetacean (whales, dolphins and porpoises) that are known to do this.

Recent analysis of a 1.4 million year old fossil named Polychronis Stamatiadis, an ancestor of the false killer whale which was discovered on the island of Rhodes, Greece in 2021, revealed it only ate small fish. The fossil is also related to the line of whales that evolved to become orcas and both descend from a common ancestor.

The five metre fossil, which lived during the Pleistocene period, was named Rododelphis stamatiadisi in honour both of Rhodes and of the collector, Polychronis Stamatiadis. It had small teeth which are missing the deep grooves found in its modern descendants and used to help break up large bones.

A four million year descendent of orcas (called Orcinus citoniensis) found in Italy in the 19th century also had small teeth, providing further evidence that the evolution to hunt larger prey was a relatively recent occurrence.

The new discovery also has implications for a popular belief that baleen whales, such as blue and fin whales, evolved to such a large size to avoid predation by orcas. It is now clear that they had already become large whales a few million years before orcas changed their eating habits.

The origins of the killer whale ecomorph
Giovanni Bianucci, Jonathan H. Geisler, Sara Citron, Alberto Collareta
Published:March 07, 2022
https://doi.org/10.1016/j.cub.2022.02.041