How Did Plesiosaurs Use Their Flippers to Swim?

A recent study suggests that these aquatic reptiles used all of their flippers to move efficiently underwater.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain stuff from how stuff Works. Hey, brain stuff,
It's Christian saga. From two hundred and twenty to sixty
six million years ago, a strange order of marine reptiles
called plesiosaurs roamed Earth's oceans. Though they were a diverse
bunch in many respects, every known species did share one

(00:23):
major trait. They all had four broad, paddle like flippers,
and in most cases the hind pair almost looked like
a duplicate of the front set, both in size and shape.
That makes plesiosaurs, which were not dinosaurs but lived at
the same time, unique among ocean going vertebrates. That's because

(00:46):
no other marine reptile or mammal extinct or extent sports
four flippers of similar size. So how did this unique
body plan work. Researchers might have just found the answer.
On aug an international team of scientists published a new
study on plesiosaur locomotion. Headed by paleontologists Luke Musket. The

(01:11):
group used measurements from a pair of British species to
construct two replica flippers, one four limb and one hind
limb with three D printing technology. These were affixed to
a custom built robot which moved the replicas around in
a tank of water to see exactly how the paddles
would turn things up. Musket and company released colorful dyes

(01:34):
into the tank as well, and tracked their motion through water. Afterwards,
the scientists put the robotic legs through numerous simulations designed
to test out different swimming styles. They found that the
most energy efficient stroke called for both flippers to work
in concert. When the front limb flapped in this test,

(01:54):
it created two vortices in the water. As the current
pushed these backward, the hind flipper weaved in between them.
By capitalizing on the wake generated by its frontal counterpart,
the rear limb made its own flapping motion six more powerful,
and this finding actually contradicts a study which argued that

(02:17):
plesiosaurs swam like sea turtles, using their four limbs to
push themselves forward while their rear paddles acted as rudders.
Using the robot, muskets team also tested this existing hypothesis.
They found that the rear paddles tended to produce drag
if kept in a stationary position, but by using all

(02:37):
four paddles to actively generate thrust, a plesiosaur could move
more efficiently. However, the co authors acknowledge that, like most
aquatic animals, plesi asaurs probably adjusted their swimming style as
the situation called for it. Furthermore, the study is complicated
by the fact that several plesiosaur species had four limbs

(02:59):
that were noticeably longer than their rear ones or vice versa.
Looks like follow up research will have to take species
specific data into account. Today's episode was written by Mark Mancini,
produced by Dylan Fagan, and for more on this and

(03:20):
other topics, please visit us at how stuff works dot com.