The first killer whales ate fish, not other marine mammals

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 killer whale-like skeleton but is gray in color compared to black and white. Both predators are members of the oceanic dolphin family, and pods of killer whales have been known to aggressively hunt and eat blue whales, the largest creatures that have ever lived. However, it is not known when this predatory behavior began, and the fossil record of both species is extremely limited.

However, a study published March 7 in the scientific journal Current biologyin collaboration with Jonathan Geisler, Ph.D., Associate Professor and Chair of Anatomy, New York Institute of Technology College of Osteopathic Medicine, and Giovanni Bianucci, Ph.D., Paleontologist, University of Pisa (Italy). ) may have vital signs.

In 2020, the remains of an ancient dolphin unknown to science were discovered on the Greek island of Rhodes, which became the first clear fossil evidence of the origin of a false killer whale. Geisler, Bianucci and several other colleagues at the University of Pisa named the species Rhododelphis stamatiadisi, after the island where the fossil was found and the paleontologist who made the discovery (Polychronis Stamatiadis). For a layer of soil containing Rhododelphisthe dolphin is estimated to have lived 1.5 million years ago during the Pleistocene era.

To better understand Rhododelphisthe researchers compared its anatomy to modern killer whales and killer whales, as well as Orcinus citoniensis, the only known fossil relative of the killer whale. Judging by the width of his skull, Rhododelphis was about the same size as modern false killer whales, 13 feet long and weighing about 1200 pounds. Surprisingly, next to the fossil were the remains of his last meal: fish bones.

Like modern killer whales, orcinus he 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 Rhododelphis there were no scratches and rough splinters commonly associated with eating limbs such as mammals. Instead, their teeth had minor scratches and small chips, suggesting that both species ate fish.

The results of the study also contradict the popular theory that large whales, including the blue whale, evolved into giant bodies to avoid predation. Although the first giant whales appeared 3.6 million years ago, the discoveries of Geisler and Bianucci suggest that ancient dolphins began preying on other marine mammals, including whales, much later. Researchers believe this behavior began in killer whales during the last three million years, and false killer whales have adapted this behavior over the last 1.5 million years.

“Diversification in the oceanic dolphin family has occurred over the past five million years, but fossil evidence from the Pleistocene era is extremely scarce,” said Geisler, an expert on marine mammal evolution. ” WITH RhododelphisWe are now beginning to fill this gap and better understand the repetitive foraging evolution of oceanic dolphins—in other words, how killer whales and false killer whales have individually evolved similar skull anatomy and feeding behaviors in other marine mammals. ”

While the finds provide the first fossil record to determine when this dietary adaptation began, narrowing the timeline further will require more fossils and more research. With this in mind, the researchers are calling for future research in areas such as Greece and Italy, which are among the few areas where Pleistocene marine deposits are widely exposed.

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