Giant laziness once ruled America before humans arrived

The large elephant-sized sloth once roamed from Alaska to Argentina, carved caves with huge claws, and dived into the ocean for seaweed meals.

These ancient giants (some weighing 8,000 pounds) dominated the United States for more than 30 million years, and then disappeared about 15,000 years ago, just humans spread throughout the continent. A new scientifically published study reveals how these outstanding organisms develop their huge size and why they suddenly disappeared, depicting a picture of ecological catastrophe that lowers one of the most successful mammal populations of evolution to a species inhabited by only six small trees.

From tree man to ground giant

The study analyzed more than 400 fossils of 17 museums and ancient DNA, indicating that the huge size is not the original lazy blueprint. The earliest laziness may have been terrestrial creatures the size of Dane, but their evolutionary journey takes a dramatic turn based on their residence.

“They look like grizzlies, but five times larger,” said Rachel Narducci, a collection manager for vertebrate paleontology at the Florida Museum of Natural History and study co-author of the Florida Museum of Natural History and Research.

Trees imposed strict weight limits then as they do now. Modern slots average only 14 pounds, while their semi-translucent cousins ​​average 174 pounds. Ground species do not face such restrictions, and ultimately reaching the size that makes modern elephants different.

Climate drives revolution in scale

The study shows that lazy-sized evolution has carefully tracked climate change over 35 million years. During the warmer period of the Miocene (170-14 million years ago), laziness actually became smaller as forests favored the lifestyle of trees.

But as the earth cooled down, the ground was lazily spread. Larger bodies help them save energy and water while traveling across multiple habitats (from the Andes peaks to the Arctic forests to the coast).

Some laziness even adapts to the marine environment. “They developed adaptability similar to manatees,” explains Narducci. “They have thick ribs to help buoyancy and eat seaweed with longer noses.”

Key evolutionary modes:

• Land laziness averages 758.6 kg (1,672 lbs), optimal size
• Tree averages top at 6.5 kg (14 lbs)
• Giantism evolved independently three times in different genealogies
• Size changes are closely related to habitat preferences over 35 million years
• Among species that live in trees, the rate of evolution is faster

Their environment master

Ground laziness is not just big, they are very diverse. They climbed up mountains, crossed the desert, and even paved houses in the northern forests, extending to modern Canada and Alaska. Their impressive claws, “ambong the largest of any known mammal, living or extinct,” allowed them to excavate elaborate cave systems.

These caves have multiple purposes, from shelter to bathrooms. In 1936, paleontologists discovered a 20-foot-thick fossil lazy mound in Nevada’s walled cave, a testament to their long-term occupation of popular sites.

According to Narducci, the Florida Museum has “the largest collection of lazy North America and the Caribbean”, and according to Narducci, the study sized 117 fossil limb bones.

Human factors

What causes such a successful creature to disappear so suddenly? The timing tells a clear story. “About 15,000 years ago, you really started to see the decline,” Narducci noted.

This coincides with the human expansion throughout the Americas. Despite the continuous change in climate, the study found no correlation between temperature changes and the last 130,000 years of lazy extinction.

Protecting giant laziness from the size of natural predators becomes their downfall. As evidence suggests, the defense of human hunters is not rapid, nor is it defensive against human hunters.

Even sloths are not completely safe. The Caribbean species did not survive until about 4,500 years ago, shortly after humans arrived in the region.

What have we lost

Lazy extinction does not just represent charismatic giants. These creatures fill in ecological roles that no modern animals can replicate. Giant ground laziness is an ecosystem engineer who disperses seeds, maintains grasslands and creates habitat modifications that support countless other species.

“Including all these factors and running them through evolutionary models with a variety of different situations is a major event that has never been done before,” Narducci said of the comprehensive analysis.

The six lazy species today – all small and trees – probably because they lived in dense, inaccessible forest canopies that were rarely ventured by early humans. But they represent only a small fraction of the diversity of lazy that once flourished on two continents.

This study is a striking reminder of the speed at which humans can reshape the entire ecosystem. In just a few thousand years, one of the most successful mammal giant experiments in evolution has been reduced to a few sleepy tree dwellers – bringing the monument to the lost giant world.

Related