Editing Virginia opossum (section)

==Range==
{{more citations needed section|date=September 2018}}
The Virginia opossum's ancestors evolved in [[South America]], but spread into North America as part of the [[Great American Interchange]], which occurred mainly after the formation of the [[Isthmus of Panama]] about 3 million years ago. ''Didelphis'' was apparently one of the later migrants, entering North America about 0.8 million years ago.<ref name = "Woodburne2010">{{cite journal|last1= Woodburne|first1= M.O.|title=The Great American Biotic Interchange: Dispersals, Tectonics, Climate, Sea Level and Holding Pens|journal= Journal of Mammalian Evolution|volume= 17|issue= 4|date= 2010-07-14|pages= 245–264|doi= 10.1007/s10914-010-9144-8|pmid= 21125025|pmc= 2987556}}</ref> It is now found throughout [[Central America]] and [[North America]] from [[Costa Rica]] to southern [[Ontario]] and is expanding its range northward, northwesterly and northeasterly at a significant pace.<ref name="FFM" />

Its pre-European settlement range was generally as far north as [[Maryland]]; southern [[Ohio]], [[Indiana]] and [[Illinois]]; [[Missouri]] and [[Kansas]]. The clearing of dense forests in these areas and further north by settlers allowed the opossum to move northward. Elimination of the opossum's main predators in these areas also contributed to their expansion.   Since 1900, it has expanded its range to include most of [[New England]] (including [[Maine]]); [[New York (state)|New York]], extreme southwestern [[Quebec]]; most of southern and eastern Ontario; most of [[Michigan]] and [[Wisconsin]]; most of [[Minnesota]], southeastern [[South Dakota]] and most of [[Nebraska]].

Areas such as [[Rhode Island]] and [[Waterloo Region]] and [[Simcoe County]] in southern Ontario rarely had sightings of opossums in the 1960s, but now have them regularly; some speculate that this is likely due to global warming causing winters to be warmer.<ref>{{cite journal|last1=Walsh|first1=L. L.|last2=Tucker|first2=P. K.|year=2017|title=Contemporary range expansion of the Virginia opossum (Didelphis virginiana) impacted by humans and snow cover|journal=Canadian Journal of Zoology|volume=96|issue=2|pages=107–115|doi=10.1139/cjz-2017-0071|hdl=1807/81311|hdl-access=free}}</ref> Some people speculate the expansion into Ontario mostly occurred by opossums accidentally being transferred across the [[St. Lawrence River|St. Lawrence]], [[Niagara River|Niagara]], [[Detroit River|Detroit]] and [[St. Clair River|St. Clair]] rivers by motor vehicles or trains they may have climbed upon. As the opossum is not adapted to colder winters or heavy snow, its population may be significantly reduced if a colder winter with heavier snow occurs in a particular northern region.

The Virginia opossum was not originally native to the West Coast of the United States. It was intentionally introduced into the West<ref name="FFM" /> during the [[Great Depression]], probably as a source of food,<ref>''The Opossum: Its Amazing Story'', William J. Krause and Winifred A. Krause, University of Missouri-Columbia, 2006, p. 23, {{ISBN|0-9785999-0-X}}, 9780978599904.</ref> and now occupies much of the Pacific coast. Its range has been expanding steadily northward into [[British Columbia]].

Small isolated populations of Opossums also occur in Eastern [[New Mexico]] and parts of Southern and Central [[Arizona]], particularly around [[Tucson, Arizona|Tucson]]. It is unknown if these populations are native to these regions or were introduced at some point.<ref>{{Cite web |title=Opossums in Arizona? – Arizona Daily Independent |url=https://arizonadailyindependent.com/2017/01/22/opossums-in-arizona/ |access-date=2025-02-08 |website=arizonadailyindependent.com}}</ref>