What is Sinodelphys?
{{italictitle}}{{Taxobox | name = ''Sinodelphys'' | fossil_range = [[Lower Cretaceous]] | domain = [[Eukaryote|Eukaryota]] | image = Sinodelphys szalayi.JPG | image_width = 250px | image_caption = ''Sinodelphys szalayi'' fossil displayed in Hong Kong Science Museum. | regnum = [[Animal]]ia | phylum = [[Chordate|Chordata]] | classis = [[Mammal]]ia | subclassis = [[Theria]] | infraclassis = [[Metatheria]] | genus = [[extinction|†]]'''''Sinodelphys''''' | species = †'''''S. szalayi''''' }} '''''Sinodelphys''''' <ref>informally known as the [[China|Chinese]] [[opossum]]</ref> is an [[extinction|extinct]] [[mammal]] from the [[Lower Cretaceous]]. It is a member of the infraclass [[Metatheria]], the group which contains modern [[marsupial]]s. To date, it is the oldest [[metatheria]]n [[fossil]] known, estimated to be 125 million years old. This makes it almost contemporary to the earliest [[Eutheria|placental]] fossils, which have been found in the same area.<ref>Ji, Q., et al. [http://www.nature.com/nature/journal/v416/n6883/full/416816a.html The earliest known eutherian mammal], ''Nature'', 416, pp. 816-822, April 2002.</ref> It was discovered and described in 2003 in rocks of the [[Yixian Formation]] in [[Liaoning]] Province, [[China]], by a team of scientists.<ref name=Luoetal2003/><ref>Rincon P. [http://news.bbc.co.uk/2/hi/science/nature/3311911.stm Oldest marsupial ancestor found], [[BBC]], December 2003.</ref><ref>Pickrell, J. [http://news.nationalgeographic.com/news/2003/12/1215_031215_oldestmarsupial.html Oldest marsupial fossil found in China], ''[[National Geographic]]'', December 2003.</ref><ref>Klinger M.A. [http://www.carnegiemnh.org/news/03-oct-dec/sinodelphys/sino2_72.jpg Sinodelphys szalayi] {{Webarchive|url=https://web.archive.org/web/20120222071415/http://www.carnegiemnh.org/news/03-oct-dec/sinodelphys/sino2_72.jpg |date=2012-02-22 }}, ''Carnegie Mellon Natural History'', 2003.</ref> ''Sinodelphys szalayi'' grew only 15 cm (5.9 in) long and possibly weighed about 30 g (1.05 oz). Its fossilize