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In July 1999, David Krause He was enjoying the temperate climate of Madagascar while digging the ground for dinosaurs. The island’s soil was fertile ground for life in ancient times. At the end of the Cretaceous period, 66 million years ago, Madagascar, which was already an island at that time, having started from a drifting India some 20 million years earlier, dragged itself along with the legendary reptiles of the time, from theropods carnivores up to a 20-foot-long constricting snake.
That’s why three years later, when Krause opened a plaster jacket containing the fossils from the excavation, the last thing he expected to find was a mammal.
However, there it was. Stuck in the mold, along with a small, old crocodile, was Adalatherium huia stubby-tailed Cretaceous mammal, exquisitely preserved after its disappearance in a landslide. The oldest mammal found to the south of the equator, Adalatherium It had a unique set of characteristics that set it apart from all other living animals at the time, as well as from Gondwanatheria, the mysterious mammals that evolved as the supercontinent Gondwana separated.
“Once the jacket was open, I recognized an elbow joint and knew it was a mammal,” says Krause, a paleontologist at the Denver Museum of Nature and Science and lead author of the article. “I didn’t sleep for two days, I was so excited.”
Studying the fossil remains of Adalatherium It took almost 20 years, as the researchers tried to decipher each turn and transform its strange morphology, from the toes to the teeth. Last week a new article was published in the magazine. Nature, describing the finding.
Cretaceous mammals, skinnier and more modern-looking than their contemporary giants and squamous, were few and far between, especially in the southern hemisphere, which has fewer fossil deposits and less scrutiny than the northern hemisphere. The mammals that preceded the impact of an asteroid in modern Mexico, catalyzing the mass extinction event that killed the dinosaurs, were generally restless, a useful trait to bend down to survive a global cataclysm, but problematic when it comes to finding fossils. . Adalatherium was a clear exception to that rule.
“It was a giant in its day, in the sense that during the Cretaceous, most mammals were the size of a shrew or a rat,” says Krause. “This thing is about 100 times bigger than your standard home mouse.”
Adalatherium it was a product of the island effect, which postulates that large creatures shrink into isolated landmasses, while small creatures grow large. Perhaps inspired by a couple of reptilian goliaths residing in Madagascar in the Cretaceous era, Adalatherium it grew to the size of a small dog.
In addition to its unusual size, Adalatherium it had a set of traits that make it an “outlier” on the evolutionary timeline, even compared to the strange fossas, lemurs, and aye-ayes that now inhabit the island nation. With the forelimbs tucked together under his body but the hindlimbs extended on either side, it was a walking paradox. Among other things, it had a hole in the skull just above the nose that paleontologists still don’t fully understand, even after two decades of study and analysis. Adalatherium It also boasted two pairs of upper incisors and posterior teeth that defy explanation.
“Teeth are the standard to observe through early mammalian evolution,” says Krause. “These teeth are really rare. There’s nothing like that in any living or extinct mammal. “
When the asteroid hit, Adalatherium it was among the many mammals wiped out from Earth. However, Madagascar’s unique modern fauna evolved.
How do you ask Krause suggests that life may have found a way in large rafts of vegetation, deriving from Africa, a theory that has been raised for various combinations of species and continents, Madagascar is a particularly attractive subject given its proximity to Africa, and the amount of Remains that are still washed up on the east coast of the continent after heavy storms.
“If this happens within our insignificant lives, what are the chances of success for more than 65 million years?” Krause says. “The improbable becomes much more probable with the passage of time.”
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