Body size of the extinct Megalodon indeed off the charts in the shark
world

Date:
October 5, 2020
Source:
Taylor & Francis Group
Summary:
A new study shows that the body size of the iconic gigantic or
megatooth shark, about 15 meters (50 feet) in length, is indeed
anomalously large compared to body sizes of its relatives.



FULL STORY ==========================================================================
A new study shows that the body size of the iconic gigantic or megatooth
shark, about 15 meters (50 feet) in length, is indeed anomalously large compared to body sizes of its relatives.


========================================================================== Formally called Otodus megalodon, the fossil shark that lived nearly
worldwide roughly 15-3.6 million years ago is receiving a renewed look
at the significance of its body size in the shark world, based on a new
study appearing in the international journal Historical Biology.

Otodus megalodon is commonly portrayed as a super-sized, monstrous
shark, in novels and films such as the 2018 sci-fi thriller "The Meg,"
but it is known that the scientifically justifiable maximum possible
body size for the species is about 15 meters (50 feet). Nonetheless,
it is still an impressively large shark, and the new study illuminates
exactly how uniquely gigantic the shark was, according to Kenshu Shimada,
a paleobiologist at DePaul University in Chicago and lead author of
the study.

Otodus megalodon belongs to the shark group called lamniforms with a rich fossil record, but the biology of extinct forms is poorly understood
because these cartilaginous fishes are mostly known only from their
teeth. Based on measurements taken from present-day non-planktivorous lamniforms, the study presents an equation that would allow estimations
about the body length of extinct forms from their teeth. The study
demonstrates that O. megalodon that reached about 15 meters (50 feet)
is truly an outlier because practically all other non-planktivorous
sharks have a general size limit of 7 meters (23 feet), and only a few plankton-eating sharks, such as the whale shark and basking shark,
were equivalent or came close to the size. The study also reveals
that the Cenozoic Era (after the age of dinosaurs, including today)
saw more lamniform lineages attaining larger sizes than the Mesozoic
(age of dinosaurs) Era.

Warm-bloodedness has previously been proposed to have led to the gigantism (over 6 meters, or 20 feet) in multiple lamniform lineages. The new
study proposes their live-bearing reproductive strategy with a unique cannibalistic egg-eating behavior to nourish early-hatched embryos to
large sizes inside their mother to be another possible cause for the
frequent evolution of gigantism achieved by lamniform sharks.

Understanding body sizes of extinct organisms is important in the context
of ecology and evolution. "Lamniform sharks have represented major
carnivores in oceans since the age of dinosaurs, so it is reasonable
to assert that they must have played an important role in shaping the
marine ecosystems we know today," said Shimada.

"This is compelling evidence for the truly exceptional size of megalodon," noted co-author Michael Griffiths, a professor of environmental science
at William Paterson University in Wayne, New Jersey. Co-author Martin
Becker, also a professor of environmental science at William Paterson University, added, "this work represents a critical advancement in our understanding of the evolution of this ocean giant."

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


========================================================================== Journal Reference:
1. Kenshu Shimada, Martin A. Becker, Michael L. Griffiths. Body,
jaw, and
dentition lengths of macrophagous lamniform sharks, and body size
evolution in Lamniformes with special reference to `off-the-scale'
gigantism of the megatooth shark, Otodus megalodon. Historical
Biology, 2020; 1 DOI: 10.1080/08912963.2020.1812598 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201005005923.htm

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