Every time I make a video about an extinct
fossil creature I’m reminded there’s a lot of confusion out there about what is and
isn’t a dinosaur. And you’d be forgiven for being kinda confused. I mean, why is this a dinosaur, but this isn’t. And this is, but this isn’t? What about this? Dinosaur? No. But this is? Maybe paleontologists are just messing with
us. Or… maybe the question of what is and isn’t
a dinosaur goes deeper than we think? Well, like an intrepid fossil hunter, I set
out to dig up an answer, and what I found teaches us a lesson about how hard it is to
build a picture of the past when you only have a few puzzle pieces, and a lot about
why we classify things the way we do. Hey smart people, Joe here. You might be surprised to learn just how many
different types of -saurs there are There are lots of different groups, mostly
of reptiles, that have “saur” in their name. Oh yeah, that’s paleontologist Steve Brusatte I study dinosaurs and all sorts of other fossils,
but mostly dinosaurs. And I wrote the book “The Rise and Fall
of Dinosaurs” a couple of years ago. There’s pterosaurs (those are the pterodactlys),
plesiosaurs, There are mosasaurs and pliosaurs, and ichthyosaurs there’s even groups like
lepidosaurs, these are still around today. That’s just a very common root-word, it
basically means lizard. (I think it’s greek) It is Greek [look down], I checked. And we can’t forget everyone’s favorite
not-a-dinosaur, Dimetrodon, which actually predates the dinosaurs and is more closely
related to us mammals than T. rex or any of the other “saurs”. And Basilosaurus? That thing’s an early whale! Clearly, there’s a tendency to call any
extinct, scaly thing with teeth a dinosaur, even when they’re not. But to figure out what dinosaurs are, we need
to go back to when they were invented. Ok, I mean the ancient reptiles we call “dinosaurs”
evolved… more than 200 million years ago, but the word “dinosaur”? That arrived around 1841… …thanks to Sir Richard Owen, who is giving
me some strong Argus Filch vibes. Guys like Owen had made careers out of naming
and organizing all the animals and bones the very friendly and not at all problematic British
Empire was bringing to their doorstep from across the globe. One strange bone had been pulled from a quarry
in England in the 17th century, which, thanks to its odd shape was originally misidentified
as the thigh of a Roman War Elephant, and later misidentified again as… oh… heh…
oh my! Well, I’m not saying that. Some very posh gentleman scientists of England
eventually realized this and other bones came from an extinct reptile, and they named it
Megalosaurus, meaning “great lizard”. Very original, guys. When Argus… I mean Richard Owen studied these and the
bones of another reptile named Iguanodon, he decided they had enough traits in common
to be their own group, and… …it was Richard Owen, who came up with that
name, “Dinosauria,” the terrible lizards. …And then from that point on people found
more and more of these giant, ancient things in rocks all over the world. And people started to name new species, and
they started to classify things as “dinosaurs”. People from indigenous and other cultures
around the world had been uncovering evidence of these weird extinct creatures for a long
time. Like this Native American art in Utah inspired
by footprints in the surrounding rock. Posh gentleman scientists didn’t “discover”
these creatures, but they gave them “official” scientific names and began building a system
to organize them. And one of those posh gentleman scientists
influenced the way we think about and organize living things more than any other: The Smeagol
of the HMS Beagle, the acorn that planted the tree of life… my boy Chuck Darwin. Before Darwin, there were ways of putting
living things into categories. Remember this? But Darwin’s world-changing idea was that
things that are closely related also share ancestry, and if you follow the trail of common
ancestors back far enough, everything comes down to one great common ancestor of life. After Darwin, people didn’t just sort things
into different buckets based on certain traits or features, they organized them based on
a system of shared ancestry, and how those traits or features change over time. It was kind of a big deal. So when we take Richard Owen’s original
definition of “dinosaur”, and apply Darwin’s new way of looking at how things are related,
we get something close to our modern definition of dinosaurs: Iguanodon, megalosaurus… so you take them,
you go down to their common ancestor, and anything that falls within that part of the
tree is a dinosaur… Now the shape of this tree has changed and
will continue to change over time as scientists find new dinosaurs with new traits that are
related in new ways. But the tree always stays rooted in that common
ancestor. So how do we decide if something goes on the
tree? There are a few general rules. Swimming things, not dinosuars. Flying things, also not. And if the thing runs around like this, chances
are it's not a dino either. But to really map out those branches, scientists
use long lists of traits and characteristics, enough to fill textbooks, that they can measure
and plug into computer algorithms and figure out not only if a new fossil belongs in the
dinosaur group, even what sub-branch and sub-SUB-branch they belong to on the tangled tree that grew
from that common ancestor. We don’t even know for sure what that common
ancestor was, and it wouldn’t have been too different from its closest relatives that
aren’t dinosaurs. But everything that descended from that thing
is a dinosaur, because that’s what we say a dinosaur is. And this is where it gets kind of weird. Because there’s nothing in nature that says
a dinosaur has to be this. It’s just a convention. An agreement. The same way a baseball game only works because
everyone agrees to play by the same rules. I mean, think of borders on a map: The boundary
separating northern Illinois from Indiana is a made up thing. It’s only a line with cornfields on both
sides. Nothing in nature that says the boundary has
to be here. It could be here, or here. But because a group of people agreed to put
it here, and everyone agrees that the boundary is here, it’s a useful made up thing. It lets us group things together, it lets
us separate things, and it lets us organize things inside those boundaries. And just like a state or national boundary,
the definition of a dinosaur is something we made up. Definitions for pterosaurs, plesiosaurs, and
all the other saurs and not-a-saurs? We made those up too. But even though they’re made up, they’re
useful. And even though the details of the definitions
can change over time, everyone agrees to change with them. And that is what lets science happen. So a dinosaur is a pigeon, and a triceratops,
and all the descendants of their most common ancestor, thanks to a guy named Richard Owen,
a dude named Charles Darwin, and that thing. But… You can easily imagine a world, where in the
victorian times in England, some other well-connected, wealthy posh high-society person discovered
a beautiful skeleton of say a pterodactyl, you could see how Richard Owen, when he made
his definition of a dinosaur, he might have included the pterodactyls in that definition. Then the convention would have been different,
and eventually, the definition we would have put on the family tree would have included
pterodactyls. It’s easy to see how little changes in the
history of how we discover and study things, have big effects on how we later classify
and define things. So maybe somewhere in the multiverse, there’s
a world where pterodactyls are dinosaurs. And even if the science they do there is a
little different from ours, as long as everyone agrees, it’s just as valid as the science
we do here in this universe. Except for this guy [Dimetrodon]. I don’t care what universe you’re in,
still not a dinosaur. That's just wrong Stay Curious
