It occurred to me over the weekend that Tim the T-Rex has taken quite a few pictures with quite a few dinosaurs over the past several years.
Since we've been doing #Museumpalooza, Tim and I have taken pictures with Tyrannosaurs and/or their close friends and relatives at California Academy of Sciences, Denver Museum of Nature & Science, Natural History Museum of LA County, the American Museum of Natural History in New York and Chicago's Field Museum, just to name a few.
But in the back of my mind, looking at these photos made me wonder: how many of the fossils in these images are actually real?
WAIT...WHAT? OF COURSE THE FOSSILS ARE REAL. (DUH.)
Obviously, dinosaurs (and their fossils) are real things that really existed. But that is not to say that all the fossils in all of these pictures are real.
In fact, quite a few of them are likely casts made from real fossils – that is, molds taken from the outside of real fossils, which are made with anything from plastic to fiberglass.
In the meantime, while the casts are out on display, those real fossils could actually be in a laboratory undergoing rigorous study, or stored in a really cool climate-controlled basement somewhere due to their age/delicacy.
BUT WHY WOULD MUSEUMS DISPLAY CASTS INSTEAD OF ACTUAL FOSSILS?
- Supply and demand. Every natural history museum wants a signature, household-name dinosaur skeleton for their lobby (as well they should) but the reality is that we haven't dug up a lot of complete dinosaur skeletons yet...definitely not enough to go around to every museum that wants one.
What's the solution? Make casts from fossils of existing dinosaur specimens. This allows that dinosaur to be seen and enjoyed at different institutions throughout the world even if it's not there "in the flesh", so to speak.
- Casts really tie the skeleton together. VERY rarely are complete dinosaur skeletons dug up straight out of the ground. Prehistoric scavengers might have made off with a leg, a river might have washed away a vertebrae or three – things can happen during the 65 million year interval between a dinosaur's death and subsequent unearthing.
But do museum visitors really want to see a T-Rex missing its leg, or an Apatosaurus / Brontosaurus that's missing a large chunk of its tail? (Short answer: no.) So casts are often made of the missing bones from another dinosaur skeleton of the same species, which helps fill in the gaps for the specimen who's missing bits of its anatomy.
- Fossils can be delicate flowers. While they may have aged for a few millennia, bones are still bones – that is, fragile and capable of breaking, no matter how hard they may appear.
Plus, dinosaur skeletons in museums aren't held together with duct tape and super glue. Most installations involve some degree of potential damage to the bone: a pin hole for a wire here, a suspension rod there, and of course there's the problem of forcing a few foot/leg bones to bear the weight of the rest of the fossilized skeleton.
That doesn't even cover fluctuating humidity levels in the room, the vibrations caused by passing museum visitors, or countless other external factors...believe it or not, in spite of surviving some 65 million years (give or take), some fossils just can't handle the stress.
- Casts are light. Related to "fossils can be delicate flowers", is the fact that fossils – especially fossils of the permineralized variety (where minerals seep into the bones and fill up all the available space) can be very, very heavy.
Weight can make real fossils difficult to display, because they require stronger and more obvious support structures that can take away from the visual effect of the freestanding dinosaur skeleton, especially if you want your dino displayed in striking, dynamic poses.
Take Sue, for instance – the largest, best preserved and most complete T-Rex ever discovered – who lives at the Field Museum in Chicago.
The head on this skeleton of Sue is a cast. Her ACTUAL head is nearby, in its own case on the museum balcony, because her ACTUAL head weighs 600 pounds and can't be supported by the real bones of her fossilized T-Rex neck.
Of course, Sue's head didn't weigh 600 pounds while she was alive, but then her skull wasn't a fossil back then – it was bone, much lighter and easier to move around. Her skull's weight increased drastically once she died and the fossilization process began. In her defense though, when scientists discovered Sue, her skull weighed a full ton – paleontologists got it down to about 600 pounds after removing all the solid rock from her fenestrae (the holes in her skull).
- Fossils may serve a higher purpose elsewhere. Let's say a PhD student barges into your museum because he needs to study your Triceratops specimen's hip so he can turn the entire state of dinosaur taxonomy on its head. (FYI: Dinosaur taxonomy WAS actually [potentially] turned on its head last month, which is absolutely fascinating and which Dustin Growick's "Dinosaur Show" explains far better than I ever could.)
Anyway, your Triceratops hip is currently attached to your museum's Triceratops skeleton, which would involve a lot of expensive de-installation headache to remove, and a second headache whenever the research was finished and the bone had to go back on the specimen. That's a lot of stress on the bone, as well as on the museum installation team. Keeping the cast on display and the real thing in the archives saves that stress.
- Casts can look better...AND they can be replaced! Sometimes skeletons aren't all the same color. Sometimes skeletons aren't all from the same animal. Whatever the reason, your fossils look less than visually consistent. So it goes in Hollywood, so it goes in paleontology: plastic to the rescue, for all your superficial anatomical needs!
As an added bonus: if a visiting toddler gets overexcited, slips the barrier and hugs the femur of your resident T-Rex skeleton, never fear! It may have scratched up your cast, but at least no damage was done to that valuable, uber-important REAL T-Rex femur hiding in the basement!
BUT I WANNA SEE ACTUAL FOSSILS...
...and you can, and often do! The good news is that many natural history museums use a combination of real bones and casts in the majority of their dinosaur displays these days. Also, if a specimen is predominantly composed of fossil casts, the museum usually labels them as such. (If they don't, they should.)
But the reality is that museums have to balance the wants and needs of the visitor ("real fossils, right now!") with the safety and well-being of the specimens that they've been entrusted to safeguard. Take heart though – any casts that you see at your nearest museum were, at one point, made from real, fossilized dinosaur bones, and given the choice between seeing actual fossils or not seeing any dinosaur at all...well, I know which I would choose.