About 62 million years ago — just 4 million years after an asteroid the size of Mount Everest hit Earth and ended the age of dinosaurs — furry creatures with finger-like fingers on their feet emerged as the first to roam the planet of large mammals. These animals are about the size of a large dog, towering over the shrew-to-possum-sized mammals that existed before the space rock hit, and now scientists think they know how these critters outshone their small mammalian cousins.
In a new study published Wednesday (August 31) in the journal nature (opens in new tab)Researchers analyze fossil teeth and bone of Pantolambda Bathmodona robust, now extinct mammal that weighed about 92 pounds (42 kilograms) in adulthood.
“They might get a little bigger [than the analyzed specimens]So this is pushing 100 lbs [45 kg]which is quite large when you consider the fact that this is a mammal that lived only 4 million years later Tyrannosaurus Rex extinct,” said lead author Gregory Funston, a researcher at the University of Edinburgh during the study. Mesozoic [252 million to 66 million years ago]so panto ramda said Funston, who now works at the Royal Ontario Museum in Toronto, Canada.
But what’s the secret to their impressive size? According to this new study, P. Bathmodon likely evolved into large, highly developed infants, similar to modern newborns giraffe and hippo, jumped out of the womb ready to walk. In order to be smooth sailing, P. Bathmodon A baby may first be conceived in the mother’s womb for about seven months, nourished by the placenta.
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“Today, placentas appear to be unique among mammalian groups in that they have long gestational periods leading to larger, more developed young adults, but it is unclear when in their evolutionary history placental mammals evolved to be longer gestation period,” says Gemma Louise Benevento, postdoctoral researcher in macroevolutionary paleontology at the Senckenberg Center for Biodiversity and Climate Research (SBiK-F) in Germany, who was not involved in the study.
The new study provides evidence that, 62 million years ago, P. Bathmodon He was able to carry out months-long pregnancies, Benevento told Live Science in an email, and showed that this reproductive strategy may have contributed to the explosion in body size of various placental mammals following the extinction of non-avian dinosaurs.
How mammals got so big
physically, P. Bathmodon It looks like a mashup of several modern mammals that exist today.
“In some ways it looks like a dog, in others it looks like a bear,” Funston told Live Science. The animal has a long, thin tail and feet, somewhat like a human hand, as well as fingers and nails. Notably, P. Bathmodon Not having a large head to match its massive body, suggesting that its ancestors increased in size before their brain size; Recent research shows (opens in new tab) This “first force” evolutionary pattern can be seen in many placental mammals that emerged after the end-Cretaceous extinction.
To learn more about the life history of this quirky mammal, Funston and his colleagues analyzed 12 P. Bathmodon Specimens, including a total of 23 bones and a mixture of 22 teeth from adults and juveniles.All of the fossils originated in the San Juan Basin in New Mexico, where paleontologists have previously discovered a bone bed, or a fossil-laden rock formation, most of which is P. Bathmodon specimen.
“By sampling all these specimens from one location, one bone bed, it gives us a little bit of an advantage because it represents a single community in time,” Funston said. Collecting samples from a number of people ranging in age from about 2 to 11 years old at the time of death allowed the team to estimate how fast the animals grew and how long they lived.
What’s more, by looking for specific chemical signatures in the animals’ teeth and bones, the study authors were even able to determine when each individual became pregnant in utero, when they were born, and roughly when they were breastfeeding.This kind of tooth analysis has only been done before on modern animals and some 2.6 million-year-old primate fossils, but never before on animals as old as this P. Bathmodon.
The technique takes advantage of the fact that as a tooth develops, the hard outer enamel and underlying dentin tissue build up every day, like the growth lines of a tree. In addition, the cementum, the hard tissue that covers the root, adds an additional layer each year. Located between these growth rings is a unique “birth line” that occurs in both adult and infant teeth, albeit in a slightly different location in the tooth structure.
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Birth lines contain high concentrations of zinc because shortly after birth, mammalian mothers produce a special, highly nutritious milk called colostrum, which is rich in minerals. Then, after the mother stops producing colostrum and begins producing normal breast milk, the birthing line gives way to a layer of tooth tissue rich in barium — an element that is incorporated into teeth and bones in a similar way to calcium during lactation.
by taking thin slices P. Bathmodon Teeth — thin enough to let light through — the researchers were able to spot these unique lines of zinc and barium.Analysis shows P. Bathmodon They were just over seven months pregnant, and their babies were only able to breastfeed for one to two months. By then, according to an analysis of their bones, the young men will weigh about 20 pounds (9 kilograms), Funston said.
at birth, a P. Bathmodon A newborn “may be moving. It may have fur all over its body. Its eyes may be open, and it may have a full set of teeth,” Funston said. Soon after birth, the growth rate recorded in the animal’s skeleton was so rapid that it likely reached sexual maturity in its first year of life.According to research, most P. Bathmodon Instances died between the ages of 2 and 5, but the oldest lived to 11 years of age.
“Compared to the lifespan of a wild mammal of the same size, most of our specimens die at about 3 or 4 years old, so that’s really, really fast,” Finston said.
If this bizarre dog-bear mashup carries its cubs for long periods of time before giving birth to big babies, other placental mammals may do the same. That could explain how the mammals suddenly grew in size after the dinosaur-killing asteroid hit Earth, he said.
If applied to other fossils, the geochemical tooth 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 dental changes in 60+ million-year-old mammals and from these data infer gestational length, weaning age, and age at death for individuals,” she said. “Teeth are abundant in the mammalian fossil record, so applying this technique to the Mesozoic and Cenozoic [66 million years ago to now] Mammal fossils open up new and exciting possibilities. “
“In the future, if possible, I would like to see this technique used in even older groups of mammals from the Mesozoic,” she said.
Originally published on Live Science.