(ORDO NEWS) — Australia is well known as the home of the most unusual mammals on the planet. Now, however, Australian scientists have said that this southern continent is the distant ancestral home of all modern placentals and marsupials, from where they set off to conquer the world about 126 million years ago.
Scientists have long believed that the first therians viviparous mammals that include marsupials and placental species evolved in the Northern Hemisphere.
As evidence for this view, the richness of the mammalian fauna on the northern continents and the large number of fossils found there have been cited.
However, having studied the fossilized bones of early therians living in Madagascar, South America and India, the researchers concluded that viviparous animals appeared in the Southern Hemisphere almost 50 million years earlier than in the Northern Hemisphere.
This means that their distant ancestral home should not be sought in Eurasia or North America, but among the southern continents.
After studying the fossils of mammals found in Australia, paleontologists have come to the conclusion that they have much in common with modern therians and their Jurassic predecessors, who lived mainly in the southern hemisphere, on the territory of the Gondwana supercontinent.
Apparently, the direct ancestors of Therians originated about 180 million years ago in the south, and only in the early Cretaceous period, about 126 million years ago, did they penetrate the Northern Hemisphere.
Immediately after their arrival, therians became very diverse and numerous: thanks to their unique teeth, capable of processing food extremely efficiently, they occupied many ecological niches, displacing their distant relatives, primitive mammals, from them.
Ironically, having succeeded on other continents, placental mammals practically disappeared in Australia, and by the time humans appeared on the mainland, only a few species of bats and rodents lived there.
However, due to the efforts of people, the diversity of Australian placentals has increased rapidly, and now feral cats, foxes, rabbits and rats are one of the main threats to the survival of unique Australian animals.
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