The only order in the subclass Metatheria is the Marsupial order. It has experienced great development since it originated from the ancestors of ancient mammals in the Cretaceous period. It is widely distributed around the world and competes with each other in a more or less equal position with the primitive placental mammals. However, with the advent of the Cenozoic Era, placental species began to show stronger evolutionary advantages, causing marsupials to decline greatly and eventually become extinct in most continental areas.
thylacine
However, in both areas, marsupials continue to exist in a "paradise" isolated from the rest of the world.
One area is Australia, which was completely separated from the Asian continent during the Cretaceous or at the end of the Cretaceous before placental species had time to invade. Without competition from placental species, marsupials were able to fully develop and produce a broad adaptive radiation (evolving like rays to occupy various ecological niches), giving rise to carnivorous quolls and herbivorous marsupials. Lagomorphs and diprodents. To this day, marsupials are still the dominant mammals in Australia; carnivores such as thylacines and Tasmanian devils chase various kangaroos, playing a similar role to wolves, badgers, various deer, cattle and sheep in the hinterland of the Asian continent. ecological role.
Possum - a living American marsupial
The other region is South America, which was isolated from North America due to isthmus rupture in the early Tertiary Period. Before isolation, it harbored a fauna that included marsupials and primitive placentals. After isolation, because advanced placental species had no chance to enter from the North American continent, marsupials were able to continue to evolve and develop, becoming strong competitors for the remaining primitive placental descendants. They lived quite successfully until the end of the Tertiary Period, when South America was once again connected to North America through the isthmus. Highly evolved placental species invaded from the north. Fierce competition resulted in the destruction of most marsupials and The primitive aboriginals had the extinction of placental species.
The development of marsupials in other areas is limited. They lived in Eurasia during the early and middle Tertiary Period, but later disappeared from these areas.
animal tags： Thylacine possum kangaroo wolf badger deer cattle sheep
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