Pleistocene overkill, the notion that humans overhunted megafauna near the end of the Pleistocene in the Americas, Australia, and beyond, is used as prime example of the impact that humans can have on the planet.

First proposed in 1966 by paleontologist Paul Martin, this “overkill hypothesis” stated that the arrival of modern humans in each new part of the world brought with it the extinction of all those huge animals, whether through hunting them or outcompeting them.

The first is that human over-hunting directly caused the extinction. The second is that over-hunting eliminated a “keystone species” (usually the mammoths or mastodon) and this led to environmental collapse and a more general extinction.

There are three main hypotheses to explain this extinction: climate change associated with the advance and retreat of major ice caps or ice sheets. “prehistoric overkill hypothesis”

The end of the Pleistocene was marked by the extinction of many genera of large mammals, including mammoths, mastodons, ground sloths, and giant beavers. The extinction event is most distinct in North America, where 32 genera of large mammals vanished during an interval of about 2,000 years, centred on 11,000 bp.

Research suggests extreme climates, not humans, wiped them out. Human activities and population growth have wrought much destruction to life on Earth. But when it comes to megafauna extinctions, evidence suggests we may be off the hook – rather, the major culprit could be climate change.

Direct killing by humans, primarily for meat, is the most significant factor in contemporary megafaunal decline. A number of other mass extinctions occurred earlier in Earth’s geologic history, in which some or all of the megafauna of the time also died out.

Humans did not drive Australia’s megafauna to extinction – climate change did. These megafauna were the largest land animals to live in Australia since the time of the dinosaurs. Understanding the ecological role they played and the environmental impact of their loss remains their most valuable untold story.

Many mammoth carcasses may have been scavenged by humans rather than hunted. Some cave paintings show woolly mammoths in structures interpreted as pitfall traps. Few specimens show direct, unambiguous evidence of having been hunted by humans.

The extinction of megafauna around the world was probably due to environmental and ecological factors. It was almost completed by the end of the last ice age. It is believed that megafauna initially came into existence in response to glacial conditions and became extinct with the onset of warmer climates.

After most of the dinosaurs went extinct at the end of the Cretaceous period, 66 million years ago, mammals took over as the largest creatures on land—and they became really big. But during the late Pleistocene, from around 125,000 years ago, these megafauna started disappearing.

One of the last known groups of woolly mammoths died out because of a lack of drinking water, scientists believe. The Ice Age beasts were living on a remote island off the coast of Alaska, and scientists have dated their demise to about 5,600 years ago.

It’s generally thought when resources in an environment are limited, some species decrease in size to reduce their total energy needs. Interestingly, evolution of a smaller body size seems to happen most often in insular habitats, most notably on islands – known as “island dwarfism”.

about 25,000 years ago

red kangaroo

Diprotodon

The first recorded Diprotodon remains were discovered in a cave near Wellington, New South Wales, in the early 1830s by bushman George Ranken and Major Thomas Mitchell; the latter sent them to England for study by Sir Richard Owen.

Similar to living wombats and koalas, Diprotodon was quadrupedal and browsed plant material. Diprotodon, however, was much larger, standing about 1.8 metres (about 6 feet) tall at the shoulder and measuring as much as 4 metres (12 feet) long.

40,000 years ago

The first arboreal koalas probably evolved from a terrestrial wombat-like ancestor, perhaps to take advantage of a food resource not being utilized by others.

Koalas: They’re downright adorable, and that’s obvious. Photographer Joel Sartore says koalas really are as cute as they seem. “They’re pretty much exactly what you think,” he says. Here, two joeys cling to each other at an animal hospital in Australia.

IZZY’S KOALA WORLD follows the real life of 11-year-old Izzy Bee, who helps her wildlife veterinarian mom rehabilitate koalas. Izzy lives with her parents on Magnetic Island, an Australian island that’s home to many wild koalas.

Like a lot of young people, 11-year-old Izzy Bee has a special bond with animals. Unlike a lot of young people, she shares it with one of the planet’s most cuddly: koalas.

Young koala caretaker Izzy Bee and her family rescue cuddly creatures in need and help them head back into the wild on Australia’s Magnetic Island. Watch all you want.

Young marsupials stay close to Mom! Like all marsupial babies, baby koalas are called joeys. A koala joey is the size of a jellybean! It has no hair, no ears, and is blind. Joeys crawl into their mother’s pouch immediately after birth, and stay there for about six months.

Baby koalas, called joeys, eat their mothers’ poop. The pap helps the baby grow, and is full of the mom’s gut bacteria, which could help prepare the joey for its adult diet of eucalyptus leaves. Number 2. Like many other marsupials, the penises of male koalas have two prongs.

13 – 18 yearsIn the wild

In the average female’s 12-year life span, she may produce five or six offspring over her lifetime. Once conceived, it is only 35 days before the birth of the baby Koala, called a “joey”.