In 1990, fossil collectors in South Dakota stumbled across a dinosaur that turned out to be a
really big deal. Not just because it was a T. rex – basically the most popular dino out there – or
because it ended up in Chicago’s famous Field Museum… but because of the number of bones it had.
Hi, I’m Kate and this is MinuteEarth. The dino, now named SUE, was such a big deal because of how
“complete” it was: the fossilized skeleton had 250 of the 380 or so bones that had once made up the
living dino. Which might not seem like that much, but the vast majority of dinosaur fossils we find
are just a few bone fragments or a single tooth. We don’t tend to find complete specimens because,
while becoming a fossil is pretty unlikely in the first place, the fossilization of an entire
skeleton is even more unlikely. When prehistoric critters like dinos died, their bodies would get
torn apart by predators and scavengers; their bones would get scattered by flowing water,
trampled by herds of animals, and weathered by the sun and wind. So most skeletons got broken
up before they even had a chance to fossilize. Only occasionally would skeletons escape all
this wear and tear and get buried completely – or even mostly – intact. And when they did,
they were often in places without the right chemistry for fossilization, so they just
decomposed. Any skeletons that did fossilize still had to make it through tens of millions
of years of geological upheaval that shuffled up entire layers of rocks. Even if a skeleton
made it complete through all that, it still has to be discovered at the perfect moment in
order to stay complete: when there’s been enough erosion to expose the fossil, but not enough to
weather away big parts of the fossil itself. So even mostly-complete skeletons like SUE’s
are really, REALLY rare. But there are a few conditions that can protect a dinosaur’s skeleton
from being lost to time. Like when a dino was killed and buried at the same time – in, say,
a volcanic eruption or a torrent of mud that scientists call a “debris flow.” Because these
skeletons got buried right away, they have a much better shot at staying intact than skeletons that
just lay around for a while. Second, since smaller dinos required a lot less sediment to bury,
they were more likely to get covered up, and therefore to end up complete. Finally,
more common dinos – like the herbivorous Maiasaura – simply left behind more skeletons than rarer
dinos did, so it’s more likely that they would make it through the fossilization gantlet whole.
SUE was a T. rex – a relatively large, relatively uncommon dino – therefore, a relatively unlikely
candidate to end up so complete. But it happened anyway, probably thanks to a giant debris flow.
Which is lucky for us, because not only is the fossil AMAZING to look at, its
completeness has taught us lots about the anatomy, biomechanics, and even daily life of a T. rex.
But then again, the fact that a series of very unusual events was required to preserve that
skeleton so well means that SUE isn’t particularly representative of how most dinos died, or the
conditions that normally scattered and weathered their bodies; to learn about those things,
we have to study those more common, less-complete fossils. So while finding SUE was amazing,
you might say that finding any dino fossil, no matter how complete, is pretty SUE-perb.
SUE is SUE-per cool, and we’re so glad we got to dig into this story for you. But we can’t tell
these amazing science stories without your support. There are tons of ways to support
what we do here at MinuteEarth: You can join the community of Minutearthlings on Patreon,
where you’ll be a part of Patreon-exclusive behind-the-scenes drawings, comics,
director’s chats, giveaways, and other fun stuff. Or you can head to our merch store,
which we’re busy stocking with new stickers, pins, shirts,
and other surprises you can’t find anywhere else. And that’s where you can buy our first book,
which you can also find at Amazon. And, last but not least, liking, subscribing,
and sharing our videos goes a long way - and it means a whole lot to us. Thanks for watching!