A common controversy you’ll see brought up in discussions on biology is whereas opossums are what most people would consider stupid or whereas they’re some misunderstood genius. Some people say that they are as smart as dogs, others that they are as dumb as chickens. One might want to rethink the later analogy since chickens are nowadays understood to be rather sophisticated animals, but whatever.
The history of the study of marsupial intelligence is one filled with biases and assumptions. For a long time scientists assumed placental mammals were “superior” to the more “primitive” marsupials, a notion only further supported by the fact that the most iconic marsupials such as kangaroos and koalas are in fact pretty stupid. But a fairly recent study has in fact showcases that there are perceived biases in understanding the brain size of marsupials and placentals: the aforementioned dumb diprotodontians are seen as the “marsupial standard” while primates are seen as the “placental standard”. Obviously, we get skewed results with this perception.
Still, brain size is not the end of the story, since it doesn’t necessarily translate to actual behaviours. In terms of actual cognitive performance, we get mixed results: a study on Monodelphys shows that they are capable of learning problem solving solutions, while one on Didelphys opossums shows that they are incapable of doing that. Thus, there appears to be some extreme variation in regards to the problem solving capacities of opossums, and it is very likely that this might be a species specific issue.
Maybe even on an individual level, given the contradictory descriptions of Virginia opossum intellect.
Ultimately, I think it is fair to say that opossums are not necessarily stupid by mammal standards. Understanding their behaviour and cognitive abilities will certainly give further insight on the evolution of mammalian intelligence and whereas placentals are “gifted” in this department, which so far seems to be only half the truth.