Tooth analysis confirms the megalodon - a huge ancient shark - was
warm-blooded
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[June 28, 2023]
By Will Dunham
WASHINGTON (Reuters) - The megalodon, a huge shark that was the scourge
of the ancient oceans and is a star in modern movie theaters, is named
for its "large tooth" - and for good reason. Its serrated teeth - up to
about 7 inches long (18 cm) - could tear through any prey in the deep
blue sea.
Those teeth now are providing a fuller understanding of this extinct
predator, with an analysis of the mineral makeup of their enamel-like
tissue confirming that megalodon was warm-blooded - a trait scientists
suspect contributed both to its tremendous success and eventual
downfall.
Researchers estimated that megalodon, which reached at least 50 feet (15
meters) and possibly 65 feet (20 meters) long while hunting marine
mammals including whales, boasted an overall average body temperature of
about 81 degrees Fahrenheit (27 degrees Celsius) and could keep it at
about 13 degrees F (7 degrees C) above that of the surrounding seawater.
This may have made megalodon a more dynamic predator - a strong swimmer
able to digest food in an energetically efficient manner and,
importantly, tolerate colder water, letting it broaden its range to
nearly worldwide.
Most fish are cold-blooded - ectothermic - with body temperatures
matching the surrounding water. But a few are warm-blooded - endothermic
- generating their own body heat. Examples include certain sharks
including the largest modern one, the great white.
"The only comparable living species today in terms of both diet and body
temperature are the great white shark and, to a lesser extent, the mako
shark. Though, as shown in our study, megalodon was quite a bit warmer
than both of these modern apex predators, which makes megalodon unique,"
said geochemist and paleoclimatologist Michael Griffiths of William
Paterson University in New Jersey, lead author of the research published
in the journal Proceedings of the National Academy of Sciences.
The study found that megalodon, while warm-blooded, had a lower body
temperature than whales.
"One theory is that they were regionally endothermic - that some parts
of their body were warmer than other parts, whereas body temperature is
higher and more uniform across the body in most large mammals," UCLA
atmospheric and oceanic scientist and study co-author Robert Eagle said.
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An illustration shows the large extinct
shark megalodon, Otodus megalodon, preying on a seal in this picture
obtained by Reuters on June 27, 2023. Alex Boersma/PNAS/Handout via
REUTERS.
Megalodon, perhaps the largest shark of all time, appeared about 23
million years ago, then disappeared about 3.6 million years ago amid
declining ocean temperatures and sea levels.
Warm-bloodedness could have been useful for megalodon in cooling
waters.
"Yet, the fact that the species became extinct suggests the probable
vulnerability - or the cost - of being warm-blooded because
warm-bloodedness requires constant high food intake to sustain high
metabolism," paleobiologist and study co-author Kenshu Shimada of
DePaul University in Chicago said.
"It is quite possible that there was a shift in the marine ecosystem
due to the climatic cooling that caused the sea level to drop,
altering the habitats with the populations of the types of food
megalodon depended on, such as marine mammals, possibly becoming
scarce, leading to the extinction of megalodon," Shimada added.
Scientists previously had suspected megalodon's warm-bloodedness but
the study provided the first empirical evidence. The researchers
analyzed geochemical characteristics in fossil megalodon teeth to
determine the temperature at which minerals in enamel-like tissue
formed - an indicator of body temperature.
After being overshadowed for decades in popular culture by the great
white - think the 1975 blockbuster "Jaws" and its endless progeny -
megalodon is now in the spotlight thanks to the 2018 film "The Meg"
and its upcoming sequel "Meg 2: The Trench."
"Megalodon is primarily represented only by teeth and a handful of
vertebral specimens in the fossil record," Shimada said. "Contrary
to novels and movies that portray megalodon as a super-sized,
monstrous shark, the fact is that we still don't even know exactly
how it looked or how it lived. This is exactly why the 'science of
Megalodon' continues to be an exciting academic field."
(Reporting by Will Dunham, Editing by Rosalba O'Brien)
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