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The reason why some animals do and some don't is because of necessity. On land most animals have either an internal skeleton (with a backbone) or an external skeleton (beetles with shells). Underwater, however, animals like jellyfish and octopi have no need for backbones, because there is less of a pull from gravity. They have no real need for a backbone, so they don't grow one.
What else can I help you with?
Why some animal have wings and why some not?
some animals develop wings. others get it from traits. such as genetic traits. others well i dont know about that
What are some carnivorous savanna animals?
dont know dont care :)
Does flying animals eat fish?
some do some dont
Why are animals dumped on?
=some people dont like animals they like to abuse them instead.=
Why are some plants cold and others hot?
some have peploe on it and some dont
Why do some symbol have a slash across them and others dont?
*
Why some animals have no bones?
Some animals have no need of them, jellyfish for instance. Others have an exoskeleton, insects are an example.
How do animals eat porcupines?
some porcupines have quills on their nose but some dont so animals eat em by the nose.
Why is the swamp important to animals?
swamps are important to animals because some animals bathe in it and others drink it.
What are some similarities of animals and man?
Scientists put animals in groups because many animals are different than others. For example, some animals have backbones others do not, some animals lay eggs others give birth, Some animals are able to live in harsh environments like the desert while others cannot. Scientists group animals together that are almost exactly alike. Like a lion and a cheetah, they both give birth to live young, both are in the cat family, both are warm-blooded, both are predators,... and the list could go on and on!
What do animals provide humans with?
Some animals provide food and others are used for their fur
Why are some animals blood hotter than others?
because some animals live in water and there blood is colder
