Early killer whales ate fish -- not other marine mammals

Date:
March 7, 2022
Source:
New York Institute of Technology
Summary:
A new study provides vital clues on when killer whales began
feeding on other marine mammals.



FULL STORY ==========================================================================
Only two species of cetaceans (dolphins, whales, and porpoises), prey
on other marine mammals: the true killer whale, or orca, and the false
killer whale, which has a skeleton similar to the orca but gray coloring
vs. black and white.

Both predators are members of the oceanic dolphin family, with pods of
orcas even known to aggressively hunt and eat blue whales -- the largest creatures to ever live. However, it is unclear when this predatory
behavior began and fossil records for both species are extremely limited.


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Now, a study published March 7 in the scientific journal Current
Biology, co- authored by Jonathan Geisler, Ph.D., associate professor and department chair of anatomy at New York Institute of Technology College
of Osteopathic Medicine, and Giovanni Bianucci, Ph.D., a paleontologist
at the University of Pisa (Italy), may hold vital clues.

In 2020, the remains of an ancient dolphin unknown to science were
found on the Greek island of Rhodes, providing the first clear fossil
evidence for 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 earth that contained Rododelphis, it is estimated that
the dolphin lived 1.5 million years ago, during the Pleistocene epoch.

To better understand Rododelphis, the researchers compared its
anatomy to today's false killer whales and orcas, as well as Orcinus citoniensis, the orca's only known fossil relative. Based on the width
of its skull, Rododelphis was roughly the same size as modern false
killer whales, measuring 13 feet long and weighing approximately 1,200
pounds. Surprisingly, next to the fossil were remnants of its last meal:
fish bones.

Much like modern orcas,Orcinushad very powerful jaw muscles and sharp interlocking teeth. However, these teeth were smaller than those of
today's orcas, and there were more of them. Interestingly, the teeth
of both Orcinus and Rododelphis lacked the rough scratches and chipping commonly caused by eating limbed prey, such as mammals. Instead, their
teeth had fine scratches and little chipping, suggesting that both
species ate fish.

The study's findings also contradict the popular theory that large whales, including the blue whale, evolved giant bodies to avoid predation. While
the first giant whales emerged 3.6 million years ago, Geisler and
Bianucci's findings suggest that ancient dolphins began preying on other
marine mammals, including whales, well after this. The researchers believe
that this behavior began in orcas within the last three million years,
with false killer whales adapting this behavior within the last 1.5
million years.

"The diversification of the oceanic dolphin family occurred within the
last five million years, but fossil evidence from the Pleistocene epoch
is exceedingly rare," said Geisler, who is an expert in marine mammal evolution.

"With Rododelphis, we're now beginning to fill this gap and better
understand the repeated evolution of feeding adaptations in oceanic
dolphins -- in other words, how both orcas and false killer whales
separately evolved similar cranial anatomy and the behavior of feeding
on other marine mammals." While the findings provide the first fossil
data for determining when these feeding 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 regions where Pleistocene marine sediments
are extensively exposed.

========================================================================== Story Source: Materials provided by
New_York_Institute_of_Technology. Note: Content may be edited for style
and length.


========================================================================== Related Multimedia:
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Life_reconstruction_of_the_Pleistocene_false_killer_whale_and_graphics_of
craniums ========================================================================== Journal Reference:
1. Giovanni Bianucci, Jonathan H. Geisler, Sara Citron, Alberto
Collareta.

The origins of the killer whale ecomorph. Current Biology, 2022;
DOI: 10.1016/j.cub.2022.02.041 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220307132059.htm

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