Quadrupedalism is a form of movement on land that involves
using four limbs or legs. Likewise, a quadruped is any animal
that moves with four limbs or feet. Most quadrupeds have
backbones and spinal columns such as dogs, cats, deer,
cows, and alligators. Snakes and shellfish are not
quadrupeds. Insects are generally not quadrupeds, although
there are some exceptions, the most famous of which is the
praying mantis.

Although humans are not quadrupeds, the term can be used
to refer to a human whose body weight is entirely supported
by both arms and legs. Some people move around on their
arms and legs as an exercise for full body strength building.
The movements can be modified in several ways such as
changing speed or pointing the posterior part of the body
higher or lower.
Dogs and cats are quadrupeds.
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In July 2005, a group of siblings was discovered in Turkey who learned to walk on all
fours due to a genetic disorder that impaired their ability to walk upright. The family was
featured in a documentary called “The Family That Walked on All Fours.”

Ancestors of humans used to walk on all fours until the lower back was bent upwards to
assume an erect trunk posture.
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Animals with four limbs (e.g., legs, arms, wings, fins) are not all
classified as quadrupeds. They are all referred to as tetrapods
because arms and wings are considered legs that have been
modified through evolution. Thus, birds would be considered
tetrapods as they have two legs and two wings. Most birds only use
their wings to fly but not to walk which is why they are not
quadrupeds. While birds are not quadrupeds, the shoebill has been
known to use its wings to stabilize itself after going after prey. Some
marine animals such as seals are tetrapods. Snakes are also
referred to as tetrapods even though they do not have their legs
anymore or only have evidence of residual limbs (such as boa
They are classified this way due to their ancestry. Quadrupedalism comes from the Latin word "quattuor"
meaning "four," and the Latin word "ped" meaning "foot." Put the words together and you have "four foot."