The Virginia opossum has a small brain case compared to other animals its size.
Researchers measured this by filling a clean, dry cranium with dried beans. An opossum brain case held 25 dried beans; a cat brain case held 125; and that of a raccoon held 150.
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"Thus, the opossum has one of the smallest brain-to-body size ratios among mammals and it was generally assumed that the larger the brain size to total body ratio the more intelligent the animal is," University of Missouri researchers William J. and Winifred A. Krause write in The Opossum: Its Amazing Story.
Also, "if held by the neck and the other hand used to support its back, the opossum simply gives up, relaxes and often clasps its forepaws together in a prayer-like pose."
But opossums are not "stupid," they write.
They have a "remarkable capacity to find food and remember where it was found," the Krauses write. "When tested for their ability to remember, opossums scored better than rats, rabbits, dogs and cats, but did not score as well as humans. Opossums can remember the taste of noxious or toxic substances even a year after a single encounter."
The protruding eyes look black because the pupils stay dilated in all but the brightest lights -- a night vision adaptation that isn't helpful in the day. But eye tests suggest the opossum can learn to discriminate black and white, colors, patterns and geometric forms.
"Additional studies designed to measure the opossum's ability to solve maze problems indicate that mature opossums were superior to most species (rats, cats) in maze learning tasks," the Krauses write.
Most of the brain is the animal's olfactory bulbs, which are already functional at birth and probably help it follow a saliva trail their mother lays down by licking a path toward the opening of her pouch.
Still, captive possums that are overfed become cross-eyed because of fat accumulation behind the eyeballs. In other words, they do store fat in their heads.
-- Celia Storey
ActiveStyle on 04/24/2017