(water splashes)
(ominous music)
- [Narrator] Sea monsters are considered
to be mythical creatures at
the center of tall tales.
(lighting crackling)
But science tells a story
of real-life monsters
lurking in Earth's prehistoric seas,
monsters called plesiosaurs.
Plesiosaurs were ancient marine reptiles
that first appeared about
215 million years ago.
They belonged in the order Plesiosauria,
which is divided into two groups:
the long-necked plesiosaurs
and the short-necked pliosaurs.
Plesiosaurs were massive animals.
They grew up to 43 feet long,
with large bodies and
small, triangular heads
with smooth sharp teeth.
Their most signature feature
was their long necks.
Spanning half the length of their body,
plesiosaur necks had up
to 76 distinct vertebrae,
over 10 times more than
that found in humans.
Older depictions portray these necks
as willowy and snake-like,
but recent discoveries have shown
that they were, in fact, relatively stiff.
This allowed the plesiosaurs
to stay streamlined
while swimming or while
hunting fish, squid, and clams.
While the Plesiosaurs evolved
long necks and small heads,
their pliosaur cousins went
the opposite direction.
Their necks were short and
their heads were large,
measuring up to 10 feet long.
But much like plesiosaurs,
pliosaurs were massive,
growing up to 50 feet long
and weighing almost 100,000 pounds.
Despite their large size,
pliosaurs were excellent swimmers,
capable of reaching speeds
near 10 kilometers per hour.
Their speed, along with their great size,
allowed pliosaurs to
become ferocious predators,
devouring large marine animals
and even other Plesiosauria.
Despite their differences,
pliosaurs and plesiosaurs
shared a few key features
that were characteristic
of the genus Plesiosauria.
They used all four of
their flippers to swim
in a form of underwater flight,
similar to the movement of a dragonfly.
And while they spent their
entire lives in the sea,
plesiosaurs had no gills.
Rather, they were air-breathers,
coming up to the surface for
oxygen before every dive.
By about 66 million years ago,
these powerful predators died out;
but today, they continue to
be a point of fascination,
inspiring legends as grand
as the monsters themselves.
