Paleontologists have identified the first 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 dinosaurs died out.
They made the breakthrough by studying the dental (tooth) equivalent of tree rings (growth lines and elements preserved in fossil teeth) that they used to reconstruct the day-to-day life of one of our first cousins: Pantolambda bathmodon, a lucky one pig-dog-like creature, which trotted about 62 million years ago, shortly after the extinction of the dinosaurs.
In doing so, he revealed it Pantolambda mothers they were pregnant for about seven months, before giving birth to a single, well-developed baby with a mouthful of teeth, who nursed for only 1-2 months before becoming fully independent.
“For 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 chemical fingerprints of birth and weaning in teeth that are so old,” said Professor Stephen Brusatte of the University of Edinburgh, who was involved in the research.
Placental mammals account for the majority of mammal species alive today, from humans to tiny shrews to 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 give birth to large, well-developed babies that 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, precisely when this lifestyle arose has been a mystery. Because the bones of early mammals were small and fragile, fossilized remains of, say, hip bones, which could be used to gain information about species’ reproductive styles, are often missing. The teeth are better preserved, the size and shape of which 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 reconstruct things like its gestation period, how long it nursed, when it reached maturity, and how long it lived, things that we couldn’t do in fossil mammals before. Now.” , said Dr. Gregory Funston of the University of Edinburgh, who led the research.
In the event that PantolambdaFunston was surprised to discover how advanced this trait seemed at this point in mammalian evolution.
“One of the closest analogues in terms of their development is things like giraffes, which are born right on the plains and have to move within seconds or else they’ll be hunted,” he said. “We would have expected that these kinds of life stories would have emerged slowly, and then become more and more specialized over time, but what we’re seeing is that Pantolambda, just 4 million years after the extinction, it is already experiencing this completely new life story.”
Funston hopes the study could open a new frontier in research into fossil mammals and how they evolved. “This method opens up the most detailed window we could hope for into the everyday lives of extinct mammals,” he said.
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