>>DANNY BARTA: Many people think that 
pterosaurs are dinosaurs because
they're reptiles and they lived 
at the same time as dinosaurs.
But pterosaurs are not actually dinosaurs in the scientific sense.
So when we call something a dinosaur,
we mean that belongs to the group
Dinosauria which was named by
Sir Richard Owen in 1842.
And within Dinosauria there's three main groups.
You have the Ornithischian dinosaurs like
Triceratops and Stegosaurus,
and you have the long-necked Sauropod dinosaurs like
Patagotitan and Apatosaurus,
and you also have the Theropod dinosaurs which
includes the very famous Tyrannosaurus
as well as our birds that we see all
around us today.
So when we think about biological classification,
each group is
nested within a larger group.
Dinosauria is nested within a larger group called Archosauria.
Archosauria includes the close cousins of the dinosaurs - the pterosaurs that we talked about earlier -
as well as the crocodile line archosaurs
which includes today's crocodiles and alligators,
as well as a number of extinct forms - 
some of whom actually were dinosaur mimics.
You may have even seen extinct 
crocodilians in a museum and
thought they were dinosaurs, because they look so similar.
Pterosaurs and dinosaurs are distinguished from 
all the crocodile line archosaurs
on the basis of the arrangement of their ankle bones.
Dinosaurs and pterosaurs separated from one another
nearly 250 million years ago
on the basis of having a
hole in their hip socket and a 
long crest on their upper arm bone.
250 million years ago is really a very long time geologically,
so dinosaurs and pterosaurs, while they may be 
close cousins in an evolutionary sense
are really quite widely separated.
Now, there are flying dinosaurs; we just call
them birds today.
Many other prehistoric animals often get confused with dinosaurs
like the sail-backed mammal relative Dimetrodon as well as fossil mammals themselves,
the giant ground sloth or woolly mammoth.
People also think sometimes 
that large marine reptiles,
like plesiosaurs, ichthyosaurs, and mosasaurs,
are dinosaurs themselves. You
may think that an animal is a dinosaur
because it's large and scaly, but these traits
evolved much earlier in evolutionary history.
Just because pterosaurs aren't dinosaurs 
doesn't make them any less amazing.
They ruled the skies for over a hundred and fifty million years,
and I think that's really cool.
