Edinburgh, September 19 (Conversation) 62 million years ago, a mother gave birth to a child. After overcoming the trauma of birth within minutes, the baby began to explore the world around him. The baby began to suckle from its mother, a natural instinct shared by all animals of its kind, mammals.
Every day she grew, and after a month or two, she began to be fed a diet of buds and leaves. He could have become independent soon after, but tragedy happened. Only two and a half months later she died.
But the story of this child does not end there. Because after 62 million years, its cousins (humans) discovered its skeleton, fossilized in the harsh desert of New Mexico, in the southwestern United States.
Classified as a type of early mammal, it is a bear-like animal called the Pantulamba Bathmodon. The group to which this species belongs (Pantodonta) became extinct in the Eocene epoch, about 10 million years after the birth of the fossil child, leaving no living descendants.
His bones and teeth and I and an international team of scientists used to reveal his life in unprecedented detail. Our findings may help explain how mammals such as Pantolamba took over the world after the dinosaurs went extinct 66 million years ago.
Your skeleton tells the story of your life. Trapped within the dense minerals of your pearly smile, tiny streaks mark each day the growth of your teeth, which continue to grow inward for most of your life.
Their chemistry reveals your diet. The building blocks of your diet are recycled to build up your tissues, while retaining their original chemical fingerprints. Your bones grow like trees, leaving annual rings.
So your skeleton acts like a kind of journal, recording some of the major events you face, like childbirth, starvation, or injuries. Scientists can detect such braces by cutting bones and teeth into very thin slices so that light can shine through.
We did this for the baby fossil Pantulamba, along with several adults. We tracked the daily tooth growth of a two-and-a-half-month-old. This told us that his teeth grew rapidly, some forming in two months. Others, such as large molars, took up to six months (our molars take three years to form).
But his teeth revealed something more important. As on many of our calendars, there was an important day: his birthday. A distinctive birth line marks the day this child was born, and the same line appeared in the teeth of an adult Pantolambda as well, evidence that adult teeth began to form before birth.
Our analysis showed that Pantolambda babies were born with a full set of milk teeth, and their adult teeth replaced within a year after birth. Most mammals today have brown teeth, but they are not usually replaced for years. We’ve also looked deeper into the early life of Pantolambda by mapping out the changing chemistry of teeth. To do this, we needed a laser.
We have steamed the teeth little by little using a microscopic laser. Like a needle on a vinyl, the laser played a record of the chemical changes our bodies undergo when we are born, sick, and weaned. By matching this record with our timeline of daily growth markers, we were able to determine how long Pantolambda mothers were pregnant and how many days the baby was breastfed.
Our study, the first of its kind in fossil mammals, revealed that Pantolambda had a long gestation (seven months) and a short lactation period (one to two months). The data also shows that the lifespan of Pantolambda was very short, from four to five years, some reaching about ten years.
This lifestyle is similar to placental mammals, the group that included. It is the earliest evidence of this type of lifestyle in the fossil record.
The placenta is distinct because of our placenta. While many mammals and even other types of animals (fish, for example) have placentas, we and our relatives have a more developed placenta that provides better nutrition, waste removal, and fetus protection.
This last aspect is critical. The pregnancy of other mammals may not be long because the mother’s immune system can reject the fetus if it grows too large. Our own placenta prevents this from happening, and our study suggests that Pantulamba must have had it, too.
A longer pregnancy allows placental mammals to produce larger babies, which we assume is a shortcut to reaching larger sizes in adulthood. They are getting bigger and faster than other types of mammals.
These are the pack marsupials (including kangaroos and koalas) and egg-laying monotremes (such as the duck-billed platypus). But the story, as always in science, is not very straightforward. A recent study showed that the group of extinct, small, rodent-like mammals had placental-like reproduction, or at least short nursing periods like Pantolambda.
We now know the life history of the pantolamba better than all other fossil mammals. In fact, we probably know the life history of Pantolambda better than some of the rare mammals that currently exist (for example, one of the many species of bats recently discovered). And we owe a debt of thanks to early placenta species like Pantolamba for the amazing diversity of mammals around us today.
Although the mammals living at the same time as Pantolambda evolved so quickly that we struggle to trace their family tree, we know that they created the first mammalian-dominated ecosystems. These meek survivors who inherited Earth seized the opportunity, founding one of the greatest dynasties the planet has ever seen. (Conversation)
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