Giant soil lazy people have evolved three times different for the same reason

A refreshing and dry climate transformed the lazy into giants – before humans lead the huge animals to extinction.

Today's lazy people are famous little herbivores that move through the tropical awnings of tropical forests. But for tens of millions of years, South America housed a dizzying diversity of lazy. Many were giants living on the ground, with some giants approaching 5 tonnes of weight.

This amazing size range is particularly interesting to Alberto Boscaini at the University of Buenos Aires in Argentina and his colleagues.

“The size of the body is in correlation with everything in the biological features of an animal,” explains Boscaini. “It was a promising way to study [sloth] evolution.”

Boscaini and his colleagues have compiled data on physical characteristics, DNA and proteins of 67 lazy genres extinct and alive – groups of closely related species – to develop a family tree showing their evolutionary relationships.

The researchers then took this scalable story, which covered a period of 35 million years, and added information on the habitat, the diet and the lifestyle of each laziness. They also studied the trends in the evolution of body size, making body mass estimates of 49 of ancient and modern lazy groups.

The results suggest that the evolution of the size of the lazy body has been strongly influenced by climate and habitat changes. For example, some lazy genres have started to live in trees – similar to lazy today – and have shrunk in body size.

Meanwhile, three different lazy lines have independently evolved the elephantine proportions – and it seems that they have done so in the last million years, while the planet has cooled and the growth of the Andes has rendered South America more arid.

“Gigantism is more closely associated with cold and dry climates,” explains the team member Daniel Casali At the University of São Paulo, Brazil.

Many of these various lazy people have disappeared in two stages: one about 12,000 years ago and the other about 6,000 years ago, explains Boscaini.

“This corresponds to the expansion of Homo sapiensFirst of all, all over the American supercontinent, and later in the Caribbean, “he said – this is where some giant lazy people lived. In particular, the only surviving species live in trees, so they are much more difficult to hunt humans than massive soil lazy.

The idea that humans were death for the old megafauna is well sustained, said Thaís Rabito Pansani At the University of New Mexico, which was not involved in the study.

“However, in science, we need several evidence to strengthen our hypotheses, in particular in unresolved and very debate questions such as the extinction of the megafauna,” she says. New evidence reinforces this story.

“The lazy people were prospering for most of their history,” said Casali. “”[The findings] Teach us how a very successful [group] can become so vulnerable very quickly. »»

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