Grass, shrubs and drought: a year in the life of a giant



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A massive fossilized tooth from Central America opened a window to the life of a lazy giant who lived 27,000 years ago, according to an article in the newspaper Progress of science.

The analysis of the tooth, prized from a rim of clay located beneath the surface of a well dug in the center of Belize, reveals detailed information about what the lazy has eaten and the climate in which he lived.

The tooth belonged to a Panamerican land-sloth – Eremotherium laurillardi – a six-meter length that stretched from the southern United States to Brazil. The species would have survived for nearly two million years before its extinction, about 11,000 years ago.

Jean Larmon of the University of Illinois at Urbana-Champaign, United States, and his colleagues measured the amounts of specific chemical elements incorporated into the tooth when the sloth was alive.

The carbon 13 and oxygen 18 isotopes are particularly useful. Carbon values ​​13 can educate scientists about the types of food that laziness consumes and the levels of oxygen 18 reveal the aridity of the climate of the time.

Since amounts of these isotopes change or decrease slowly over time, they can also reveal the age of any object containing them. But there is a problem. The chemical signature differs depending on the composition of a given fossil.

In other animals, the hard outer coating of the teeth – the enamel – is generally used in the analysis of stable isotopes. But the teeth of laziness grow continually – a bit like the rat's incisors – and are therefore devoid

Larmon and his colleagues instead took readings from different layers of the lazy tooth. The values ​​have varied. Using a technique that measures the amount of light emitted by a fossil, they found that the most reliable values ​​came from a hard layer called orthodentine.

Sampling along the orthodentine layer of the tooth, the team drew a picture of the life of laziness over a period of about a year.

The animal lived in the middle of the last glacial maximum – an ice age – and before the arrival of humans in America.

At the time, Central America was not covered with tropical forests like today. The area was much drier, covered with savanna vegetation and juniper scrubland.

Laziness has had two brief rainy seasons, separated by a long dry season. His diet changed with the seasons, suggesting that it was an opportunistic food. This could have been very useful to adapt to the increasingly arid conditions of the period.

During the rainy season, he probably ate grasses and shrubs, but not leafy trees.

"It's a really solid job," says paleontologist Gilbert Price of the University of Queensland, Australia, who was not involved in the study.

"Understanding the biology and ecology of these animals while they were alive is absolutely essential."

Armed with this information, he adds, scientists are better able to evaluate factors – a changing climate, for example, or the arrival of humans – eventually led to the extinction of this species.

The reasons for the disappearance of large animals, collectively known as megafauna, remain a persistent mystery. And although this study only details the life of an individual, it contributes to a better understanding of its prehistoric environment.

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