Today, there are only two species of lazy, but historically, there were dozens, including one with a snowy with a bottle that ate ants and another which probably looked like ancestors of modern tattooles. Most of these extinguished lazy people did not live in trees either because they were too large. The greatest lazy – members of the genre Megatherum – was roughly the size of Asian bull elephants and weighed approximately 3.63 tonnes (8,000 pounds).
Ancient lazy people lived in trees, on the mountains, in deserts, boreal forests and open savannas; These habitat differences are mainly what has led to the large difference in size between lazy species. Image credit: Diego Barletta.
“They looked like grizzly ones but five times larger,” said Dr. Rachel Narducci, director of the vertebrate paleontology collection in Florida Museum of Natural History.
In the new study, Dr. Narducci and his colleagues analyzed old DNA and compared more than 400 fossils of 17 museums of natural history to understand how and why the turning extinguished have become so big.
The lazyness of the soil varied considerably Megatherum modestly large Shasta Land-pushing that terrorized the cacti in the desert in the southwest of North America.
The same cannot be said of the lazy people who have developed an affinity for climbing trees. Those who lived entirely in the canopy were and are uniformly small, with an average weight of 6 kg (14 pounds), while those who spent part of their time on the ground on average about 79 kg (174 pounds).
The lazy on the ground had a particular penchant for the caves, and their size undoubtedly played a role in their ability to find and make shelters.
Moderate size Shasta The soil lazy has favored the small natural caves annoyed by the wind and the water in the cliffs of the Grand Canyon, like the alveoli of a gigantic geological lung.
The greatest lazy people were not limited to pre -existing caves. Using claws that are among the largest of all known mammals, or known, they could screech from the naked earth and the rock. Many caves they have left are still there with a decoration of the scratches along the interior walls, proofs of their old nesting excavations.
Other factors that may have contributed to their size difference include the climate, the degree of kinship between lazy species and metabolic rates.
The ability to discriminate precisely between these several possibilities required a substantial quantity and various types of data.
The authors combined information on the form of fossils with the DNA of living and extinguished species to create a lazy tree of life which traced the lazy line until their origin more than 35 million years ago.
With this scaffolding in place, they added results gleaned from decades of research on where the lazy people lived, which they ate and if they were climbers or walkers.
Because paleontologists were specifically interested in the evolution of size, they collected data for the final analytical ingredient by measuring hundreds of museum fossils, which they used to estimate the lazy weight.
According to the team, the size differences between lazy people were mainly influenced by the types of habitats in which they lived and, by extension, climate change.
“Including all these factors and making them go through evolutionary models with multiple different scenarios was a major company that had never been done before,” said Dr. Narducci.
The lazy dynasty coincided with important changes that change life in the climate of the earth.
The oldest thing that scientists can reasonably consider as a laziness is called Pseudoglyptodonwho lived 37 million years ago in Argentina.
The team's analyzes indicate that the first lazy people would probably have been small residents on the ground, the size of a large Danish.
At various moments throughout their evolutionary history, Sloths has adopted a semi-arboreal lifestyle.
However, everyone stayed in the trees. The greatest lazy people, including Megatherum And Mylodonhas probably evolved from a lazy adapted to the trees which finally decided to remain firmly planted on the ground.
In this context of climbers and undecided walkers, the size of the lazy has hardly changed at all for about 20 million years, whatever their favorite locomotion method. So something overwhelming has happened.
A giant injury was opened between the modern state of Washington and Idaho through certain parts of Oregon and Nevada, and Magma came out.
This left a scab of almost 600,000 miles cubes in the northwest of the Pacific. It is still visible in certain places along the Columbia river, where millions of running water have crossed and polished a basalt colonade.
These rock pillars have a distinct hexagonal shape caused by the way the magma hardens and cracks while cooling.
The volcanic event that has been a slow burn that lasted around 750,000 years and was aligned with a period of global warming called the climate optimum of the Mid Miocene.
The greenhouse gases issued by the volcanic eruption are currently considered the most likely cause of warming.
The lazy people responded by reducing. This may be due to the fact that warmer temperatures have brought increased precipitation, which allowed forests to develop, thus creating more habitat for small lazy.
Reduction of size is also a common way for animals to manage thermal stress and has been documented in the fossil folder several times.
The world remained hot for about a million years after the volcano remained silent. Then, the planet took over a long -standing cooling scheme which continued to adjust and begins in the present. The lazy people also reversed the course. The more temperatures have dropped, the more bulky they have become.
The arboreal and semi-arboreal lazy people had the obvious limitation of having to live near the trees, but the lazy land lived almost wherever their feet took them.
They climbed the Andes, died out with open savannas, migrated into deserts and obsolete leaf forests in North America and made a house in the boreal forests of Canada and Alaska.
There were even lazy people suitable for marine environments. Thalassocnus lived in the strip of arid land between the Andes and the Pacific. They survived in this hard region by looking for food in the ocean.
“They have developed adaptations similar to those of the Lamantins,” said Dr. Narducci.
“They had dense ribs to help burst and longer walls to eat sea herbaries.”
These various environments have presented unique challenges that the lazy soil noted, in part, by strengthening.
“This would have allowed them to keep energy and water and travel more effectively in habitats with limited resources,” said Dr Narducci.
“And if you are in an open meadow, you need protection and be larger provides part.”
“Some lazy terrestrials also had small osteoderms in the shape of pebbles integrated into their skin.”
Equally important, the larger bodies have helped lazy people to cope with cooling climates.
They reached their greatest stature at the time of the Pleistocene ice, shortly before disappearing.
“About 15,000 years ago, it's when you really start to see the deposit,” said Dr. Narducci.
There is still a debate on what happened to the lazy people, but since humans arrived in North America almost at the same time when lazy people have disappeared en masse, it is not difficult to speculate.
Paradoxically, the large size that has sheltered them from most predators and isolated from the cold has become a responsibility.
Neither the quick nor well defended lazy, the soil and the semi-arboricole soil were easy choices for the first humans.
The arboreal lazy people looked at the carnage taking place below them from the safety of the peaks, but even there, they did not escape without losses.
Long after their loved ones who live on the ground have turned off everywhere else, two species of lazy in the Caribbean held 4,500 years ago.
Humans arrived in the Caribbean almost at the same time as the Egyptians built the pyramids. The lazy of the Caribbean trees disappeared shortly after.
“Paléoclimatic changes do not explain the rapid extinction of soil lazy that started about 15,000 years ago,” the researchers said.
“Their steep disappearance suggests man -oriented factors in the decline and extinction of lazy people.”
THE study was published in the May 22 2025 issue of the review Science.
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Alberto Boscaini and al. 2025. The emergence and disappearance of giant lazy people. Science 388 (6749): 864-868; DOI: 10.1126 / Science.adu070
This article is based on a press release provided by the Florida Museum of Natural History.
