Sunday, July 30, 2017

Who or What Killed the Megalodons?

Georgia in Megalodon's jaw
I never really thought about it much. I just assumed with changing climates and evolving prey they failed to adapt and died out, but according to this work, they may have been pushed out by Killer Whales.

 The mighty Megalodon shark may have starved to death
For many years, climate change has been considered the main reason why Megalodon disappeared. The Earth has been in a cooling trend beginning 15 million years ago, with global temperatures declining until it culminated in the last ice age that started 2.5 million years ago, roughly around the same time the shark is believed to have gone extinct. This led scientists to theorize it could not cope well with the decreased temperatures of the oceans, restricting its population to the tropics until its ultimate demise.

But a new study led by Catalina Pimiento from the Paleontological Institute and Museum of the University of Zurich analyzed 200 records of Megalodon findings and, by researching the fossils and the ecosystems in which the sharks lived, came to an important conclusion: climate conditions weren’t the main drive behind the end of Megalodon’s reign.

The team found that, within the general trend of cooling, there were fluctuations of higher and lower average temperatures during the past 20 million years, and these fluctuations should have affected Megalodon’s numbers and distribution accordingly if the traditional theory was correct. But they didn’t.
But how did climate fluctuate without human intervention?

Instead, the researchers found that Megalodon seems to have thrived consistently until a peak abundance during the Middle to Late Miocene Period, around 10-5 million years ago, after which it started to decline until extinction. The species’ collapse seems to be tied to an important point in time, rather than showing several ups and downs.

What may have happened in this crucial period, the Late Miocene, is the disappearance of many species of small to medium-sized baleen whales and the appearance of some powerful competition: orcas.

Megalodon seems to have been heavily dependent on relatively slow-moving whales for food. Those experienced great diversity during the Miocene, with many more species known from fossils of that time compared to the number of species alive today.

But then, changes in sea level and nutrient distribution in the oceans happened around 2-3 million years ago with the onset of the last Ice Age, causing the extinction of many marine mammals. The ones that survived were either too agile for Megalodon, like dolphins and porpoises, or spent most of the year in polar regions where the shark couldn’t follow. This may even have caused an increase in cannibalism, with adult sharks preying on juveniles due to the lack of other options.

The appearance of the killer whale’s ancestors may have been the final blow to Megalodon. Just like their modern descendants, the prehistoric orcas were well-adapted to living in many different oceanic conditions, from the tropics to the poles, due to their mammalian metabolism and insulating fat. Being smaller, they could also survive on smaller prey than Megalodon while competing with it by attacking larger whales in pods.

Megalodon’s decline began causing significant changes in the ecosystems of the world: average size for baleen whales increased greatly, since they no longer had a major predator to keep them in check, leading to incredible giants like the blue whale. And other apex predators, like Megalodon’s smaller cousin, the Great White shark, could occupy the spaces left vacant.

It seems that this combination of factors, only indirectly related to the Earth’s cooling, was too much for the massive sharks. Being restricted to tropical waters with not enough food to sustain their large bodies year-round, they vanished from everywhere except our collective imagination – where they’re probably going to survive for a lot longer.
So, yeah, basically, I was right.

1 comment:

  1. maybe it was the oxygen levels during the Late Miocene period?

    big critters need lots of oxygen...