About 62 million years ago – just 4 million years after an asteroid the size of Everest smashed into Earth and ended the age of the dinosaurs – mysterious creatures with finger-like numbers on their feet appeared as the first large mammals to ever roam the planet. These animals, about the size of a large dog, soar above the mammals that existed before the space rock collided, and now, scientists think they know how the creatures outperformed their small mammal cousins.
In a new study published Wednesday (August 31) in the journal temper nature (Opens in a new tab)the researchers analyzed the fossilized teeth and bones From Pantulamda Bathmodona stocky, now-extinct mammal that weighed about 92 pounds (42 kilograms) when fully grown.
“Maybe they are getting a little bigger [than the analyzed specimens]so that pays 100 lbs [45 kg]which is very large when you consider the fact that this is a mammal that lived only four million years later T-Rex “Mammals became extinct,” said lead author Gregory Vanstone, who was a research fellow at the University of Edinburgh during the study. Mesozoic [252 million to 66 million years ago]So pantolambda Vanstone, now in the Royal Ontario Museum in Toronto, Canada, said:
But what is the secret of its impressive size? According to the new study, P. bathmodon It likely evolved to give birth to very advanced, large babies, similar to modern-day newborns giraffes And the hipposI came out of the womb ready to walk. To be able to run to the ground, P. bathmodon Babies were probably first conceived in their mothers’ womb for about seven months, and they were fed by the placenta.
Related: What happened when the asteroid that killed the dinosaurs hit Earth?
“Today, the placenta appears to be unique among mammalian groups in long gestation periods, resulting in larger and more developed young, but it is not clear when placental mammals evolved in their evolutionary history to have longer gestations,” said Gemma Louise Benevento. A postdoctoral researcher in macroevolutionary palaeobiology at the Senckenberg Center for Biodiversity and Climate Research (SBiK-F) in Germany, who was not involved in the study.
The new research provides evidence that 62 million years ago, P. bathmodon They were able to withstand pregnancies for months, and suggest that this reproductive strategy could have helped diverse placental mammals explode in size after the non-floating dinosaurs went extinct, Benevento told Live Science in an email.
How did mammals get so big
physically, P. bathmodon It looked like a mixture of many modern mammals that exist today.
“In some ways it would have looked like a dog, in other ways it would have looked like a bear,” Funston told Live Science. The animal had a long, thin tail and feet somewhat similar to human hands, complete with fingers and nails. In particular, P. bathmodon He did not have a relatively large head to match his massive body, indicating that the size of his ancestors’ bodies had increased before their brain size had increased; Recent research indicates (Opens in a new tab) This pattern of “muscular pre-brain” development can be seen in many placental mammals that emerged after the end of the Cretaceous extinction.
To learn more about the life history of these strange mammals, Funston and colleagues analyzed 12 P. bathmodon The samples, which together included 23 bones and a mixture of 22 adult and juvenile teeth. All fossils originated from the San Juan Basin in New Mexico, where paleontologists previously discovered a bony bottom, or bedrock, filled with fossils, most of which were P. bathmodon samples.
“By sampling all of these samples from one site, one bone bed, it gives us some advantage because it represents one community at the right time,” Funston said. Collecting samples from several individuals, whose ages ranged from about two to 11 years at the time of death, enabled the team to estimate how quickly the animals grew and how long they lived.
Moreover, by looking for specific chemical fingerprints in the animals’ teeth and bones, the study authors could determine how long each individual carried in the womb, when they were born, and approximately how long they breastfed. Such dental analyzes have previously only been performed on modern animals and some primate fossils up to 2.6 million years old, but never before on an animal as old as P. bathmodon.
This technology takes advantage of the fact that, as the teeth develop, the hard outer enamel and underlying dentin tissue accumulate daily, in layers similar to the growth lines of a tree. In addition, the cementum, the hard tissue that covers the root of the tooth, acquires a new layer every year. Between these growth rings is a distinctive ‘birth line’ that appears in both adult and child teeth, although their positions are slightly different within the tooth structure.
Related: How tiny, furry mammals that went under the feet of dinosaurs came to take over the world
The birth line contains a high concentration of zinc, because soon after birth, mammalian mothers produce a special milk rich in nutrients called colostrum, which carries a large amount of the mineral. Then, after the mother stops producing colostrum and begins making natural breast milk, the birth line gives way to layers of dental tissue saturated with a lot of barium – an element that is incorporated into the teeth and bones during infancy in a similar way to calcium.
By taking thin slices of P. bathmodon Teeth — thin enough to shine through — the researchers were able to identify these distinctive streaks of zinc and barium. The analysis suggested that P. bathmodon They are pregnant for just over seven months and their babies are only breastfed for one to two months. By that time, the youngsters weighed about 20 pounds (9 kg), based on an analysis of their bones, Funston said.
At birth, a P. bathmodon “The baby may have been mobile. He would probably have had fur all over his body. His eyes might have been open, he might have had a mouth full of his teeth,” Vanston said. Soon after birth, the animal’s growth rate, as recorded in its bones, was so rapid that it would likely reach sexual maturity within its first year of life. According to the study, most P. bathmodon Individuals died between the ages of 2 and 5 years, although the oldest individual survived until the age of 11 years.
“Most of the specimens died out at about 3 or 4 years of age, and that’s really, really fast,” when compared to the lives of wild mammals of similar size, Funston said.
If this strange combination of a dog-bear carried her young for an extended period of time and then gave birth to large babies, other placental mammals might have done the same. He said this could explain how the mammals suddenly swelled in size after the asteroid that killed the dinosaurs hit Earth.
If applied to additional fossils, the dental geochemical analysis used in the study could shed new light on prehistoric life, Benevento told Live Science.
“The authors show that it is possible to directly measure changes in the teeth of mammals over 60 million years old, and from this data infer gestational length, weaning age, and age of death of individuals,” she said. Teeth are abundant in the mammalian fossil record, so the application of this technique to the Mesozoic and Cenozoic [66 million years ago to now] Mammal fossils open up exciting new possibilities.”
“I hope in the future to see this technique used, if possible, on older Mesozoic mammal groups,” she said.
Originally published on Live Science.
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