Early mammals lived fast and died young

Artist's impression of a female 'Pantolambda' nursing a young. / H.Sharpe

Science | Paleontology

They reconstruct, thanks to the chemical analysis of their teeth, the daily life of a species that lived 62 million years ago, shortly after the extinction of the dinosaurs

Large primitive mammals grew twice as fast as their current size and had a much shorter lifespan, according to a study published in the journal 'Nature'. This is what the growth lines of the teeth of a species of mammal that lived 62 million years ago have revealed to a group of researchers led by paleontologist Gregory Funston, from the University of Edinburgh.

When the dinosaurs became extinct 66 million years ago as a result of an asteroid impact on what is now the Yucatan Peninsula, the mammals that survived the catastrophe grew rapidly in size to occupy the niches vacated by the large lizards. One of those mammals was 'Pantolambda bathmodon', a herbivore that weighed 42 kilos, and which Funston and his collaborators describe as "a robust mixture of pig and dog".

The upper jaw of 'Pantolambda' with its teeth. /

G. Funston

An animal's life story is written in its bones and teeth, the researchers explain in Nature. The annual cycles are engraved on the bones, "the rate of growth throughout life, including changes associated with maturity." In teeth, daily growth lines in dentin and enamel store chemical information from day to day. "It's like reading your diaries, but etched in your teeth," says Funston.

The history of life in the teeth

The scientists used bones and teeth from twelve specimens of 'Pantolambda' for their study. They cut samples of the teeth so thin they were almost transparent, vaporized them with a laser, and determined the chemical composition of each. Using the growth lines of the teeth as a 'clock', the composition of the samples revealed specific vital episodes. "There are chemical changes in the teeth that reflect important transitions in the first years of life: high levels of zinc deposited at birth and barium enriched during infancy," says Funston.

Thanks to this, they discovered that the pregnancies of the females of 'Pantolambda' lasted just under seven months and that they gave birth to "a single well-developed baby with a mouth full of teeth." The calf probably moved from day one and only fed on her mother for a month or two before becoming "fully independent." The animal reached sexual maturity in the first year of life and most died by four, although some individuals reached eleven.

Reconstruction of a juvenile specimen and another adult. /

S. Shelley

"The ability to produce large babies, which mature for several months in the womb before birth, helped mammals transform from the humble mouse-sized ancestors that co-existed with the dinosaurs to the wide variety of species—from humans to even elephants and whales – that exist today”, highlights Steve Brusatte, from the University of Edinburgh and one of the authors of the research.

"We now know more about the life of 'Pantolambda' than we do about some enigmatic mammals living today!" says Funston. Brusatte is surprised that they were "able to identify the chemical traces of birth and weaning in such ancient teeth." Until now, this technique has been applied to
woolly mammoths from 17,000 years ago and to 'Australopithecus', hominids that lived 2.6 million years ago. Pantolambda is 32 times older than Autralopithecus, and reading its "dental diaries" opens the door to doing the same with other primitive mammals.

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