University of Edinburgh: Ancient mammals lived fast and died young

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Some prehistoric mammals were born ready-to-go and grew up twice as fast as today’s mammals, giving them an edge after the dinosaur extinction, a study suggests.

Research indicates that their long pregnancies explain why our early ancestors rose to prominence, some 62 million years ago, and dominated territories previously occupied by Tyrannosaurus rex, Triceratops and other giant dinosaurs.

Early mammals
An international team led by the University of Edinburgh in collaboration with the University of St Andrews, Carnegie Museum of Natural History and New Mexico Museum of Natural History and Science, used dental analysis to uncover the life history of Pantolambda bathmodon – a member of the earliest known group of herbivores, that grew to about the size of a sheep, in the post-dinosaur era.

Oldest fossil
Scientists examined razor thin sections of P. bathmodon’s teeth, which revealed the mammal’s daily growth lines, also known as bands. The team also used lasers to vaporize the teeth to expose its chemical make-up.

Chemical changes in the teeth showed major transitions in early life, including high levels of zinc deposited at birth, and enrichment with barium during the suckling period. This is the oldest fossil where these results have been seen – some 60 million years more ancient than the previous record-holder, according to researchers.

Independent young
The findings, published in Nature, suggest that P. bathmodon mothers were pregnant for just under seven months and gave birth to single, well-developed babies, sporting a full mouthful of teeth. Their babies, probably mobile from day one, suckled for only one to two months before they became fully independent.

Although the inferred gestation time matches that of today’s similarly sized mammals, this early mammal is found to have lived and died more rapidly by comparison. The data shows that P. bathmodon were independent and ready to mate before their first birthday, and lived only 3 to 4 years on average, whereas most mammals of similar size today live 20 years or more, experts say.

Our research opens the most detailed window to date into the daily lives of extinct mammals. This unprecedented level of detail shows the kinds of lifestyles that make placental mammals special, evolved early in their evolutionary history.

“We think that their babies’ longer gestation period could have nurtured large body sizes faster than other mammals, which may be why they became the dominant mammals of today.

Lead author, Dr Gregory Funston
Royal Ontario Museum, Toronto and former Royal Society Newton International Fellow, School of GeoSciences.
When the asteroid knocked off the dinosaurs 66 million years ago, some mammals survived, and they ballooned in size really quickly to fill the ecological niches vacated by T. rex and Triceratops and other giant dinosaurs.

“Being able to produce large babies, which matured for several months in the womb before being born, helped mammals transform from the humble mouse-sized ancestors that lived with dinosaurs to the vast array of species, from humans to elephants to whales, that are around today.

Professor Steve Brusatte
Personal Chair of Palaeontology and Evolution, School of GeoSciences.

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