St. Charles Park District Nature News – January 22
I can still picture the old photograph that hung in my folks’ hallway when I was growing up. It dated to around 1870 and showed my mom’s Great Grandfather and Grandmother Heyen, along with their daughters Martha, Tildie, Katie and Rachel, decked out in somber black finery. As was the custom of the day, the whole group posed ramrod-stiff, stern gazes fixed forward, looking as though they’d just experienced something distasteful. (I always imagined they disapproved of the modern world they looked out on. Then again, it was the 1970s…)
Walking past that picture multiple times a day for a decade or more, I often wondered what exactly I had in common with those German farmers from Menard County, IL. We didn’t look alike, and no doubt our behaviors differed substantially. But we were undeniably linked, and I have the family tree to prove it.
Just like opossums.
Well, maybe not exactly. While my ancestry was traced by a distant relative in Missouri, the opossum’s lineage was tracked down by a group of paleontologists from the University of Florida. And, whereas mine starts to get murky somewhere around the time of the Civil War, the opossum’s dates back to the end of the Cretaceous Period and the mass extinction that spelled the end of the dinosaurs.
That’s right, that chunky, clunky little critter you see pottering around your neighborhood on garbage night has roots that go back 65 million years.
Scientists poking around in limestone deposits in Wyoming’s White River Badlands recently discovered a skull they say belongs the forebear of the opossums we have today. Even more remarkable, their depiction of the ancient Mimoperadectes houdei looks an awful lot like our own Didelphis virginiana.
Clearly opossums had the good fortune to, early on, develop a set of behaviors and adaptations that literally have withstood the test of time. For one, they can and will eat almost anything. Invertebrates like worms and insects might make up one meal, pet food the next, then a frog or berries for dinner and garbage for dessert.
Opossums also breed rapidly and give birth to large litters—as many as 25 young at a time. Here in Illinois, breeding occurs twice a year, so their reproductive capacity is high.
And as marsupials—the only marsupial native to North America, incidentally—their young are born just 13 days after conception. These teensy creatures, weighing just 0.0056 oz. each, creep into mom’s pouch, where they are relatively protected, and stay for anywhere from 60 to 100 days. Upon leaving the pouch, they may hitch a ride on mom’s back for a couple more weeks, further extending the benefit of parental protection.
Another advantage opossums can claim is their ability to call just about anywhere home. Wooded areas are preferred, but shrubby fencerows work fine too. As do attics, garages those dark spaces under sheds and decks, and basements. (Just ask my dad about that last one.)
Although mostly terrestrial, opossums can from time to time be spotted hanging out in trees—though not by their tails, as is often rumored. It’s true their tails are weakly prehensile and can curl around objects, but they just aren’t strong enough to support the animal’s entire body weight. Besides, opossums have another really cool adaptation for moving about the branches—opposable thumbs on their rear feet.
Despite these many fine qualities, opossums often are labeled as “stupid.” Sure, they’re slow and lumbering, and their defensive displays rarely pass beyond teeth-baring and hissing; their well-known trick of “playing possum” (which actually is instinctive and not controllable) also makes them look like pushovers.
It doesn’t help that their brain is pretty small relative to their body size. (An opossum’s brain cavity holds 25 beans, a cat’s, 125.) Even so, when scientists tested the opossum’s intelligence using the ever-popular run-through-a-maze method, our marsupial friend actually performed better than its cat and rat competition.
One thing individual opossums don’t have going for them is longevity. Fewer than 10% survive their first year, and an opossum of two or three years of age is an elder indeed. The group as a whole, though, has had what it takes to survive 65 million years on this planet. And, who knows? They may be around 65 million more.
Pam Otto is the manager of nature programs and interpretive services for the St. Charles Park District. She can be reached at potto@stcparks.org or 630-513-4346.