Why are there so many marsupials in Australia?

These marsupials live under (kangaroos, Tasmanian devils, wombats, kangaroos and their cubs, Quka and koalas), but marsupials have not really begun to evolve. Australia is the kingdom of marsupials and home to furry kangaroos, koalas and wombats. There are so many marsupials on the mainland, which raises a question: Do these marsupials grow from below? "

The answer is unqualified (or "non-kolafe"). No, according to Robin Baker, a biology lecturer in university of salford, England, marsupials lived for at least 70 million years before they arrived in Australia.

"Marsupials never originated in Australia," Baker told Field Science. They are immigrants. "[Why don't all primates evolve into humans? ]

Marsupials are strange compared with most mammals. In an interview with Life Science magazine, Baker said that unlike placental mammals such as humans, dogs and whales, marsupials are relatively underdeveloped and continue to grow a ton of cubs in their mothers' pouch.

"The cubs are still alive, but they are stunted." They are basically crawling in the mother's * * *, usually in a bag. They basically stay on the * * * for a long time, feeding their mothers' milk, usually for several months. Baker said that they evolved in the Cretaceous after being separated from placental mammals at least 654.38+25 billion years ago.

These ancient marsupials thrive in North America. Baker said that there were about 15 to 20 different marsupials in Loresia, and now they are all extinct. It is not clear why these marsupials perform so well. But for some reason, marsupials came to South America about 66 million years ago when the savage dinosaurs became extinct. At that time, North America and South America were not as closely connected as they are today. But the two continents are so close that a land bridge or a series of islands may connect them. Baker said that this connection enables various animals to expand their trampling range.

Once in South America, marsupials and their close relatives spent a day in the wild. After they arrived, they frantically diversified between 2 million and 3 million years. For example, marsupials and their close relatives evolved into carnivores the size of bears and weasels, and one of them even evolved into saber teeth. Others evolved to eat fruits and seeds.

"What is happening in South America is that they are evolving to fill the niche that must be filled by placental mammals in the northern continent," Baker said.

Marsupials have sword-shaped teeth. (AMNH, L.Gardner/Copyright) Since then, many marsupials have become extinct, but South America is still the focus of marsupial research today. There are 100 kinds of opossums, 7 kinds of Schleius opossums and the lovely Monito del Monte, whose Spanish name is translated as "Little Monkey on the Mountain". By the way,

In the past 654.38+0 million years, an opossum from South America migrated northward and now lives in the northern part of the United States. Baker said that this is the Virginia opossum, the only marsupial in northern Mexico. "kdspe" and "kdsps" are also different orders in which opossums belong to opossums. Baker said that opossums are native to Australia and New Guinea, closely related to kangaroos, and have some anatomical differences that South American opossums lack, such as the enlargement of lower incisors.

So, how did marsupials come to Australia from South America? [Will there be another pan-continent? ]

The journey under the sun lasted until about 40 million to 35 million years ago. South America and Australia are connected with Antarctica, forming a large land mass. At that time, Antabeck said that rctica was not covered with ice, but had a temperate rainforest. "This is a nice place to live."

It seems that marsupials and their relatives started from South America, strode across Antarctica and finally came to Australia. There is even fossil evidence: Baker said that there are fossils of marsupials and their close relatives on Seymour Island in Antarctica, including the close relatives who monitored Delmonte.

Australia's oldest marsupial fossil was found in Tingamara, a place near the town of Mo Gong, Queensland, 55 million years ago. Some marsupial fossils in Tingamara are similar to those in South America. For example, Chulpasia, a fruit-eating marsupial from Peru, is a close relative of another marsupial fossil discovered by Tingamarra, Baker said.

Baker said that there is another marsupial in Tingamara, Djarthia, which feeds on insects and may be the ancestor of all existing marsupials in Australia.

This is an example of an early Australian marsupial that lived 55 million years ago. Therefore, there is a big gap in the Australian fossil record. After Tingamara, the next oldest marsupial fossil is 25 million years old. Baker said: "What we saw at that time was that there was obviously a lot of diversity in Australia." When we see koalas, we see relatives of koalas, and we see relatives of spotted-tailed bears. "Basically, all the major marsupials in Australia appeared 25 million years ago," he said.

Once again, it is not clear why marsupials thrive in Australia. Baker said, but there is a view that when the situation is difficult, the mother of marsupials can abandon any developing baby in the pouch, and mammals must wait until the end of pregnancy and spend precious resources on their cubs.

Another view is that there are no placental mammals in Australia to compete with marsupials. But this view has now been refuted by a fossil tooth, which belongs to a placental mammal or a relative of a placental mammal found in Tingamara. Baker said that this shows that mammals with placenta appeared on the mainland as early as 55 million years ago.

Today, there are about 250 marsupials in Australia, about 120 in South America and only one species (Virginia opossum) in North America. In essence, the geographical location of marsupial ancestors has changed.

"This pattern is completely opposite to the situation 65438+25 million years ago," Baker said. Today's situation may not necessarily explain their situation millions of years ago.

Why can't all animals be domesticated? Why can't elephants jump? Do animals get seasick? Originally published in Life Science. "