(bass music)
- [Narrator] In the last video,
we saw how dinosaurs flourished
during Jurassic times.
Now let's dive into the
last and longest period
of the Mesozoic Era,
the Cretaceous Period.
By the end of this time,
66 million years ago,
dinosaurs will be extinct.
We continue our journey where we left off,
at Dinosaur Ridge, a
well-known site within the
Morrison-Golden Fossil Areas
National Natural Landmark.
There's a section here that contains
Cretaceous-age dinosaur tracks.
Let's look at them now.
- If you very closely, with a trained eye,
or an untrained eye, things
start to pop out at you.
Right over here to the left of me
this feature, this feature, this feature,
what does that look like?
- [Woman 1] Dinosaur track.
- [Woman 2] Toes?
- [Tim] Most definitely,
that's a three-toed dinosaur.
(bright music)
- Some things that we can learn
from dinosaur tracks, that we can't learn
from fossils, would be
how the animal moved,
were their arms right underneath them,
were their arms splayed out to the side,
how fast were they moving,
what direction were they going.
You can tell a lot about the soft anatomy
of their feet and hands, like what their
little toe pads would've looked like.
Sometimes you can even see their skin.
You can tell behaviors,
like crouching down
to get a drink or were they
bending over to get a drink.
We actually have a fossils of animals
squatting down to drink water.
We see swimming traces for all
different kinds of animals.
So you can learn a lot from trackways
that you just can't tell
from a dinosaur bone.
- Okay, so there's a
nice three-toed print.
This whole thing, this whole complex.
So what happened is, the dinosaurs,
they weren't walking up a hill,
this was a flat beach or
something like that at the time.
The dinosaurs walked,
and then sooner or later,
like on a typical monsoonal afternoon,
you know, maybe a storm brews up,
blows in a lot of rain and mud,
and all sorts of other stuff, and the mud
quickly covers these dinosaur tracks
and fills them in, where then,
100 million years later
they become exposed
to the elements of
erosion and they re-expose
these tracks that were made on that day.
Because normally, when you're
walking along the beach,
you know, you're walking along,
you turn around and your tracks are gone
as soon as the wind moves the current
or the water comes in, whatever.
But that little layer, that
represents a little mud deposit
from a storm or something, was able
to preserve these tracks,
right in this layer.
- [Narrator] The
Morrison-Golden fossil sites
also consist of a wall
of Cretaceous-age plant
and animal impressions at
the Colorado School of Mines.
There are also Triceratop tracks along
the Triceratops Trail, tucked among
the Fossil Trace Golf Course.
Let's zoom forward in time,
near the end of the Cretaceous,
when the Hell Creek
Formation was deposited.
This formation contains
near complete skeletons,
of what is probably the
most well known dinosaur,
the Tyrannosaurus rex.
(bright music)
- The dinosaurs that we
find in the Hell Creek
are very different from the dinosaurs
that we find in the Morrison formations,
for instance in Utah or Colorado.
- [Narrator] The Hell Creek Formation
can be found in parts of Montana,
North Dakota and South Dakota.
To recognize the amazing fossils
found within this formation,
the Hell Creek Fossil Area
National Natural Landmark
was designated in 1966.
Over 95% of T-rex museum specimens
have come from this area.
Let's travel there now.
Greg Ligett, a paleontologist
for the Bureau of Land Management,
tells us more about this formation
and the cool things you can find
at this one of a kind site.
- When the Hell Creek was deposited,
Montana was coastal property.
Sediments were washing
in off of the shoreline
into the remnants of, what we call
the Late Cretaceous Interior Seaway.
So, in other words, it
was along the shore.
The Hell Creek Formation is significant,
scientifically, for many reasons.
One of the things that stands out,
is the quality of the
fossils that it preserves.
It preserves, not just dinosaurs,
like Tyrannosaurus or Triceratops,
but it also preserves plants
and recently some insects,
amphibians, reptiles, fish, mammals,
so, in other words, it
captures a whole ecosystem
at the time when the
dinosaurs were going extinct.
While not within the
designated landmark boundary,
a nearby active dig, being conducted by
the Burke Museum, gives
us a real life glimpse
into what makes this area so special.
- [Excavationist] Most
of the bones are sort of
in their anatomical placement,
even though they're just articulated.
You got the head here, you got some
of the neck bones here, and the lower jaw.
This is the inside of a back bone
of a rex and that's
- [Man] Oh that's awesome.
- [Excavationist] very
typical honeycomb shape.
- We know how rapidly the
sediments in this area accumulate.
So, we can say, okay the T-rex
is 66.02 million years old,
plus whatever thickness
of sediments below that
corresponds to, so my guess is
that it'll be 66.5 or
six million years old.
Which will be on the young end of T-rexes.
It's one of the last ones around.
- [Woman] That's pretty cool.
- Ya.
- [Narrator] Little did the T-rex know
that a large meteorite would hit Earth
and trigger a mass extinction,
wiping out a majority of the
world's Mesozoic species,
including all dinosaurs except for birds.
This planet altering episode that occurred
66 million years ago is referred to as
the Cretaceous Paleogene Extension event
and is exceptionally well represented
at the West Bijou Site
NNL in northeast Colorado.
It is captured in the fossil record
by a thin band of rock
known as the K-Pg boundary,
which physically separates the time
before and after the dinosaurs.
The K-Pg boundary signifies the end
of the Cretaceous Period and the beginning
of a new era, the Cenozoic.
(piano music)
Wow, what a journey.
Over this series of three videos,
we have traveled through
three geologic periods,
covering 185 million years,
explored six NNL sites
within four different states
along the Rocky Mountain front,
all while learning about the Mesozoic Era.
That cool time in Earth's
history when dinosaurs reigned.
This is just one of the many stories
America's natural places have to tell.
And everyone of us can play a role
in helping to protect these
sites and share their stories.
- Well fossils are really
the only window we have
into the deep past history of life.
- I wanna bring my grandkids here someday
and I want the fossils to still be here.
- Just anybody visiting a
site can become a scientist
by looking around, observing
the fossils you might see,
taking notes, and then you can report that
back to a museum or to
your local park office.
- Scientists will come in and re-study
and they'll look at
some of those same bones
and find new information that
is just totally surprising.
- It's not just a matter of
collecting a new dinosaur
to put in the drawer, it's
answering a new question
or adding to our knowledge
that we have already.
- We might be just at the beginning
of what we actually can know.
(soft music)
