¿Why did the megalodon get so big and other sharks don't exceed 15 centimeters?
One of the most famous giant sharks is the megalodon, an active predator that could measure 18 meters in length and that became extinct about two million years ago.
But nevertheless, the whale shark, which exists in our days, can also reach similar dimensions, without being a predator of large prey, since it is a filter feeder that feeds exclusively on plankton, a very different diet.
Starting from this comparison, which also includes information on more than 450 species of sharks and rays, an international study, in which Juan López Catalapiedra from the University of Alcalá has participated, determines that the size of these animals is related to their feeding strategy, but also to the ability of some species of predators to retain heat in the muscles related to swimming, which is known as mesothermy.
Mesothermic adaptation allows sharks that develop it to live in different types of habitat, including cold waters. In addition, it allows them to effectively hunt large prey, since they reach higher speeds and cover longer distances. For its part, adaptation to filter diets allows us to eat the most abundant food in the ocean, plankton.
However, there are several difficulties associated with the evolution tending to gigantism. Mesothermic species need to consume large prey to maintain their high energy needs, so when these species are rare, mesothermic giant sharks are more likely to disappear.
In fact, the shortage of large dams in times of climate change drastic was the most likely cause of the megalodon's extinction.
Sharks: the most threatened
For their part, filter feeders have shown more capacity to adapt to past climate changes, although at present are at risk of ingesting large volumes of toxic microplastics found in the waters of the oceans, which also threatens their survival.
«Today there are only 20 species of sharks and rays out of the almost 500 that can exceed six meters and we could call giants. We now know that the fact that they are ecologically different, filter feeders or mesotherms, has been crucial for them to become this big. This makes them even more unique. Sadly, these species are precisely the most vulnerable to factors such as overfishing and high concentrations of microplastics in the oceans ”, concludes López Cantalapiedra.
Catalina Pimiento, Juan L. Cantalapiedra, Kenshu Shimada, Daniel J. Field, Jeroen B. Smaers, «Evolutionary pathways toward gigantism in sharks and rays»Evolution January 2019 doi: 10.1111 / evo.13680.
Images: Stock Photos - Warpaint and Mark_Kostich on Shutterstock
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