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The
Didelphimorphia order is composed of 4 recent families,
15 genera and 66 species. They are distributed throughout
a large portion of North America from southeastern Canada,
eastern United States, through Mexico to about 47°
south in Argentina, South America. Some species are
also found on some of the islands of the Lesser Antilles.
The fossil history indicates a once greater geologic
distribution as specimens have been found from the Eocene
to early Miocene in Europe and in the Oligocene in North
Africa. In their current range, their fossil history
extends from early Cretaeous to early Miocene and Pleistocen
to Recent in North America, and late Cretaceous to Recent
in South America.
The
Didelphimorphians are small to medium in size and in
many species the tail doubles the overall body length.
The smallest species are in the Gracilinanus
genus and have a head and body length of approximately
70-135 mm and a tail length of 100-155 mm. The largest
genus is Didelphia with head and body length
of 325-500 mm and tail length of 255-535 mm.
The
members of the Didelphimorphia order tend to be nocturnal
in their activity levels. Depending on species they
are arboreal, terrestrial and in one case, semi-aquatic.
Their diets are for the most part omnivorous, however
some are more insectivorous or carnivorous.
As
marsupials, the Didelphimorphians complete their development
within a pouch, but the appearance and pouch-like qualities
vary among the species. In Didelphis, Chironectes,
Philander and Lutreolina the pouch is
well defined. The other genera either do not have a
defined pouch or it consists of two longitudinal folds
of skin. Typical of all marsupials, the gestation period
is shorter than the period of development within the
pouch. At birth, the young crawl using well-developed
front legs and sharp claws into the pouch and attach
to one of the five to seven mammae to suckle almost
continuously. Young Didelphimorphians do not have the
ability to thermoregulate and are dependant upon the
mother's body heat for warmth. After leaving the pouch,
some species remain with the female for a short while,
clinging to her back when traveling.
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