Editing Opossum (section)

== Evolution ==

Opossums are often considered to be "[[living fossil]]s",<ref name = "Krause"/> and as a result they are often used to approximate the ancestral [[theria]]n condition in comparative studies.<ref name = "Krause"/><ref>{{cite journal |last1=Crompton |first1=A. W. |last2=Hiiemae |first2=Karen |title=Molar occlusion and mandibular movements during occlusion in the American opossum, ''Didelphis marsupialis'' L. |journal=Zoological Journal of the Linnean Society |date=February 1970 |volume=49 |issue=1 |pages=21–47 |doi=10.1111/j.1096-3642.1970.tb00728.x|doi-access=free }}</ref> But this is a mistake, because the oldest opossum fossils are from a more recent epoch, the early [[Miocene]] (roughly 20&nbsp;million years ago).<ref>{{cite journal|author=Goin, Francisco|author2=Abello, Alejandra|author3=Bellosi, Eduardo|author4=Kay, Richard|author5=Madden, Richard|author6=Carlini, Alfredo|year=2007|title=Los Metatheria sudamericanos de comienzos del Neógeno (Mioceno Temprano, Edad-mamífero Colhuehuapense). Parte I: Introducción, Didelphimorphia y Sparassodonta|url=http://www.scielo.org.ar/scielo.php?pid=S0002-70142007000100003&script=sci_abstract|journal=Ameghiniana|volume=44|issue=1|pages=29–71}}</ref> The last common ancestor of all living opossums dates approximately to the [[Oligocene]]-Miocene boundary (23&nbsp;million years ago) and is at most no older than Oligocene in age.<ref name=Jansa2014>{{Cite journal|last1=Jansa|first1=Sharon A.|last2=Barker|first2=F. Keith|last3=Voss|first3=Robert S.|title=The Early Diversification History of Didelphid Marsupials: A Window into South America's "splendid Isolation"|date=March 2014|journal=Evolution|language=en|volume=68|issue=3|pages=684–695|doi=10.1111/evo.12290|pmid=24125654|s2cid=10274949}}</ref><ref name="BeckTaglioretti" /> Many extinct metatherians, such as ''[[Alphadon]]'', ''[[Peradectes]]'', ''[[Herpetotherium]]'', and ''[[Pucadelphys]]'', were once considered to be early opossums, but it has since been recognized that this was solely on the basis of [[plesiomorphies]]; they are now considered to belong to older branches of [[Metatheria]] that are only distantly related to modern opossums.

Opossums probably originated in the [[Amazon rainforest|Amazonia]] region of northern South America, where they began their initial diversification.<ref>{{Cite journal |last1=Castro |first1=Mariela C. |last2=Dahur |first2=Murilo J. |last3=Ferreira |first3=Gabriel S. |date=2021-09-01 |title=Amazonia as the Origin and Diversification Area of Didelphidae (Mammalia: Metatheria), and a Review of the Fossil Record of the Clade |journal=Journal of Mammalian Evolution |language=en |volume=28 |issue=3 |pages=583–598 |doi=10.1007/s10914-021-09548-7 |s2cid=237866763 |issn=1573-7055|doi-access=free }}</ref> They were minor components of South American mammal faunas until the late Miocene, when they began to diversify rapidly.<ref name=Jansa2014/> Before that time, the [[ecological niches]] presently occupied by opossums were occupied by other groups of metatherians such as [[paucituberculata]]ns<ref name = Engelman2017>{{cite journal |last1=Engelman |first1=Russell K. |last2=Anaya |first2=Federico |last3=Croft |first3=Darin A. |title=New palaeothentid marsupials (Paucituberculata) from the middle Miocene of Quebrada Honda, Bolivia, and their implications for the palaeoecology, decline and extinction of the Palaeothentoidea |journal=Journal of Systematic Palaeontology |date=9 November 2016 |volume=15 |issue=10 |pages=787–820 |doi=10.1080/14772019.2016.1240112|s2cid=88758358 |url=https://figshare.com/articles/dataset/New_palaeothentid_marsupials_Paucituberculata_from_the_middle_Miocene_of_Quebrada_Honda_Bolivia_and_their_implications_for_the_palaeoecology_decline_and_extinction_of_the_Palaeothentoidea/4216506 |url-access=subscription }}</ref> and [[sparassodonts]].<ref name="BeckTaglioretti" /><ref name=EngelmanCroft2014>{{cite journal |last1=Engelman |first1=Russell K. |last2=Croft |first2=Darin A. |title=A new species of small-bodied sparassodont (Mammalia, Metatheria) from the middle Miocene locality of Quebrada Honda, Bolivia |journal=Journal of Vertebrate Paleontology |date=6 May 2014 |volume=34 |issue=3 |pages=672–688 |doi=10.1080/02724634.2013.827118|bibcode=2014JVPal..34..672E |s2cid=84680371 |url=https://figshare.com/articles/dataset/A_new_species_of_small_bodied_sparassodont_Mammalia_Metatheria_from_the_middle_Miocene_locality_of_Quebrada_Honda_Bolivia/1017004 |doi-access=free }}</ref><ref name=Engelman2018>{{cite journal |last1=Engelman |first1=Russell K. |last2=Anaya |first2=Federico |last3=Croft |first3=Darin A. |title=''Australogale leptognathus'', gen. et sp. nov., a Second Species of Small Sparassodont (Mammalia: Metatheria) from the Middle Miocene Locality of Quebrada Honda, Bolivia |journal=Journal of Mammalian Evolution |date=27 June 2018 |volume=27 |issue=1 |pages=37–54 |doi=10.1007/s10914-018-9443-z|s2cid=49473591 }}</ref>
Large opossums like ''[[Didelphis]]'' show a pattern of gradually increasing in size over geologic time as [[sparassodont]] diversity declined.<ref name=EngelmanCroft2014/><ref name=Engelman2018/> Several groups of opossums, including ''Thylophorops'', ''Thylatheridium'', ''Hyperdidelphys'', and sparassocynids developed carnivorous adaptations during the late Miocene-[[Pliocene]], before the arrival of [[carnivorans]] in South America. Most of these groups, with the exception of ''[[Lutreolina]]'', are now extinct.<ref name="hyperdidelphys" /> It has been suggested that the size and shape of the ancestral didelphid's jaw would most closely match that of the modern ''Marmosa'' genus.<ref>{{cite journal |last1= das Chagas Silva-Neto|first1=Francisco |last2=Pavan |first2= Silvia E.|last3=Astúa |first3=Diego |date= 26 June 2023|title=Evolution, divergence, and convergence in the mandibles of opossums (Didelphidae, Didelphimorphia). |url= |journal=Current Zoology |volume= 70|issue= 4|pages= 488–504 |doi=10.1093/cz/zoad027 |access-date=|doi-access=free |pmid=39176066 |pmc=11336674 }}</ref>