Paleontologists have identified the oldest example of a placental mammal in the fossil record to date, which could provide new insights into how our furry ancestors came to dominate the Earth after the extinction of the dinosaurs.
They made the breakthrough by studying the dental (tooth) equivalent of tree rings (growth lines and elements preserved in fossil teeth) which they used to reconstruct the everyday life of one of our earliest cousins: Pantolambda batmodon, a beefy A pig-dog-like creature that trotted about 62 million years ago, shortly after the extinction of the dinosaurs.
In doing so, he revealed that Pantolambda mothers they were pregnant for around seven months, before giving birth to a single well-developed baby, with a mouthful of teeth, which she suckled for only 1-2 months before becoming fully independent.
“Most of my career I have studied dinosaurs, but this project on mammalian growth is the most exciting study I have ever been a part of, as I am amazed that we have been able to identify the chemical fingerprints of birth and weaning in dinosaurs. teeth that are so old,” said Professor Stephen Brusatte of the University of Edinburgh, who was involved in the research.
Placental mammals represent the majority of mammalian species alive today, from humans to tiny shrews and giant whales. They give birth to relatively mature young, which have done much of their growth inside their mother, nurtured through a placenta.
Although mammals existed during the time of the dinosaurs, it wasn’t until they went extinct that mammals really began to diversify and grow. One idea is that her ability to deliver large, well-developed babies who had previously been nourished by a placenta was key to her success. This style of growth and reproduction is also what allows human babies to be born with such large brains.
However, exactly when this lifestyle emerged has been a mystery. Because the bones of early mammals were small and fragile, fossilized remains of, for example, hip bones, which could be used to gain insights into species’ reproductive styles, are often missing. Better preserved are the teeth, whose size and shape paleontologists have long studied to learn about the lifestyles of extinct mammals.
The new technique is based on this tradition. It involves cutting fossil teeth into extremely thin sections to examine growth lines and vaporizing them to understand their chemistry at different stages of development. “It allows us to look at virtually any fossil mammal and piece together things like its gestation period, how long it sucked, when it reached maturity and how long it lived – things we really couldn’t do before with fossil mammals. now,” said Dr. Gregory Funston of the University of Edinburgh, who led the research.
In the case of PantolambdaFunston was surprised to discover how advanced this trait seemed to be at this point in mammalian evolution.
“One of the closest analogs in terms of their development are things like giraffes, which are born on the plains, and they have to move in seconds or else they’re going to be hunted,” he said. “We would have expected that these kinds of life histories would have emerged slowly and then become more and more specialized over time, but what we’re seeing is that Pantolambda, only 4 million years after the extinction, it is already experiencing this completely new way of life.”
Funston hopes the study can open a new frontier in the investigation of fossil mammals and how they evolved. “This method opens the most detailed window we could hope for into the daily lives of extinct mammals,” she said.
