Looking into this, the two species are morphologically so similar and yet also both so variable in colouration that in the parts of their ranges where they overlap (e.g. in Mexico) they can be difficult to distinguish from one another [especially at night when seen spotlighting]. I found a key to Mexican opossum species, and also checked out Fiona Reed's field guide, and the best distinguishing features of living animals are the cheek colour (always pure white in Virginia Opossum - easily seen in all the photos of the National Zoo's animal - but always yellowish or cream in Common Opossum) and the colour of the whiskers (a mix of black and white in Virginia Opossum - which can be seen in the better photos, including some on Zoochat - but all black in Common Opossum). I'd imagine it was these features that made somebody question the Common Opossum identity.
These features in addition to the genetic test make me perfectly happy to accept that the animal is a Virginia Opossum.
She at least doesn't look very much like a VA opossum!
and whether it is likelier they screwed up somewhere, or that a Virginia Opossum somehow has a mutation which makes it look not-at-all-like-a-VA and a-lot-like-a-Common.
