Ameridelphia

Nordopossum ( Didelphis virginiana)

• Opossums ( Didelphimorphia )
• Mausopossums ( paucituberculata )

The Ameridelphia form one of the two major groups of mammals bag ( Metatheria ). They include, with the exception of Chiloe opossum ( Dromiciops gliroides ), which is counted to the Australidelphia, all native to South, Central and North America marsupials. The extinct Sparassodonta ( " bag hyenas " ) are counted in this group.

It is not yet certain that the Ameridelphia form a monophyletic group, ie all descendants of their common ancestor include. It is possible that the Mausopossums ( paucituberculata ) are more closely related to the Australidelphia than with the possums ( Didelphimorphia ) with which they are united here.

The limits of the group over the other bag mammals based primarily on molecular data, but also on the presence of a crown comb and a long rostrum, a trunk-like structure. Studies have also an occurring only at the Ameridelphia connection of two sperm exposed to a pair of sperm, which is considered one of the strongest arguments for the unity of the animals.

The original tooth formula was probably 5/5, 1/1, 3/3, 4/ 4, that is the ancestral species of Ameridelphia probably had both in the upper and in the lower jaw five incisors, one canine, three premolar and four molar teeth.

Distribution and habitat

Ameridelphia live exclusively in the Americas, almost all of them in South or Central America. Only the Virginia or Nordopossum ( Didelphis virginiana) has become naturalized in North America. Their habitat is very diverse, ranging from tropical forests to lush grasslands to dry regions; even a customized webbed to aquatic life form is found. Individual species will stay in up to three kilometers high, while others live at sea level.

Convergence

Especially the Mausopossums ( paucituberculata ) have developed parallel to the shrews, their ecological role they take it.

In extinct Ameridelphia there are other examples of convergent evolution: Thus, in addition types that resemble the insectivores ( Insectivora ) of the mammal group of Laurasiatheria, also forms more akin to the desert rats. Especially Protruding is the convergent evolution of large carnivores, under which one can even find marsupial versions of the saber-toothed cats with the species of the genus Thylacosmilus.

Phylogeny

The time of separation of the Ameridelphia of their sister group, the Australidelphia varies according to scientific source between 128 million and 61.7 million years. Currently, a splitting of the two lines of development before about 75 million years ago and thus in the late Cretaceous period is considered most likely.

It was not until about 35 million years ago, South America separated from Antarctica, all marsupial living on the latter continent died afterwards from the increasing icing. The South American animals were up to the formation of the Panamanian land bridge to North America successful in many ecological niches group then with today's dominant higher mammals but clearly lost the competition to shape diversity and today compared with these plays only a minor role. With the Nordopossum ( Didelphis virginiana ) managed only one way to expand their habitat significantly to the north.

System

The Ameridelphia around 90 species are now counted in 22 genera, which are spread over two extant orders:

• The opossums or possums ( Didelphimorphia ) are the large group and comprise approximately 80 species including the only North American. As the name suggests, they have a real bag in which to grow the boys. Your Body is originally regarded as right; the weight can be up to five kilograms. In the majority is at the possums to nocturnal loner.
• The Mausopossums ( paucituberculata ) only 5 species are expected. They have no real bag, but only a skin fold despite their belonging to the bag mammals. Only a few inches tall, they live mainly on insects and worms; also killing and the subsequent consumption of young rodents has been reported.
• Another order made ​​millions before 2 to 3 years extinct Sparassodonta ( " bag hyenas ").