The first killer whales ate fish, not other marine mammals

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Only two species of cetaceans (dolphins, whales and porpoises) feed on other marine mammals: the true killer whale, or killer whale, and the false killer whale, which has a skeleton similar to the killer whale but gray in color compared to black and White . Both predators are members of the oceanic dolphin family, with pods of orcas known to aggressively hunt and eat blue whales – the largest creatures to ever live. However, it is not known when this predatory behavior began, and the fossil record for both species is extremely limited.

However, a study published on March 7 in the scientific journal Current biologyco-authored by Jonathan Geisler, Ph.D., Associate Professor and Head of the Department of Anatomy at the New York Institute of Technology College of Osteopathic Medicine, and Giovanni Bianucci, Ph.D., Paleontologist at the University of Pisa (Italy ), may hold vital signs.

In 2020, the remains of an ancient dolphin unknown to science were discovered on the Greek island of Rhodes, providing the first clear fossil evidence of the origins of the false killer whale. Geisler, Bianucci and several other colleagues from the University of Pisa named the species Rododelphis stamatiadisi, after the island where the fossil was found and the paleontologist who made the discovery (Polychronis Stamatiadis). Based on the layer of soil that contained Rododelphisthe dolphin is estimated to have lived 1.5 million years ago, during the Pleistocene epoch.

To better understand Rododelphisresearchers have compared its anatomy to modern-day false killer whales and killer whales, as well as Orcinus citoniensis, the only known fossil relative of the killer whale. According to the width of his skull, Rododelphis was about the same size as modern false killer whales, measuring 13 feet long and weighing about 1,200 pounds. Surprisingly, next to the fossil were remnants of his last meal: fish bones.

Just like modern orcas, orcinus had very strong jaw muscles and sharp, interlocking teeth. However, these teeth were smaller than those of today’s orcs, and there were more of them. Interestingly, the teeth of both orcinus and Rododelphis lacked the scratches and rough splinters typically caused by eating limb prey, such as mammals. Instead, their teeth had fine scratches and little chipping, suggesting that both species ate fish.

The study results also contradict the popular theory that large whales, including the blue whale, evolved giant bodies to avoid predation. While the first giant whales appeared 3.6 million years ago, findings by Geisler and Bianucci suggest that ancient dolphins began preying on other marine mammals, including whales, long after that. Researchers believe this behavior began in killer whales within the past three million years, with false killer whales adapting this behavior over the past 1.5 million years.

“Diversification of the oceanic dolphin family has occurred over the past five million years, but fossil evidence from the Pleistocene epoch is extremely sparse,” said Geisler, an expert in marine mammal evolution. “With RododelphisWe are now beginning to fill this gap and better understand the repeated evolution of foraging adaptations in oceanic dolphins – in other words, how killer whales and false killer whales separately evolved similar cranial anatomy and feeding behavior. other marine mammals. “

Although the findings provide the first fossil data to determine when these dietary adaptations began, narrowing the timeline further will require more fossils and additional research. Given this, the researchers call for future investigations in areas like Greece and Italy, some of the few areas where Pleistocene marine sediments are widely exposed.

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