Why most of the creatures in the world have four legs, like human \ lion \ even birds?

Question

Fish is out of discuss. I wonder why?

Answer 1

All of the terrestrial vertebrates have four limbs (and thus, they are sometimes referred to as tetrapods, which literally means 'four feet').

Not only that, but they all have the same basic structure of limb bones - pectoral girdle consisting of scapulae, with the humerus as the single upper arm bones, radius and ulna as the two lower arm bones and a wrist made up of carpal bones, followed by metacarpals and digits made up of phalanges. The lower limb girdle is also nearly identical, with a pelvis, femurs, tibia/fibulla, tarsals, metatarsals and phalanges.

This incredible similarity of structure in limb bones between incredible diverse groups of organisms - chickens, frogs, salamanders, whales, lions, humans, seals, plesiosaurs, iguanas, horses, mice and platypus all have this same exact limb structure, is evidence that all of these organisms share a common ancestor that also had this limb arrangement.

Strangely enough, the remaining vertebrate group, the fish, do not all share this limb bone arrangement. Most of them have the same set-up of pectoral and pelvic limbs, but after that, there's a whole variety of totally different skeletal anatomy.

There is one group of fish that does have this limb arrangement though. Most of them are only known as fossils today, but there is one living species of this group. The sarcopterygians, or lobe-finned fish were the first known group to show this particular limb pattern. The coelacanth also possesses the pattern.

Strangely enough, the earliest known fossils of amphibians look amazingly similar to sarcopterygian fish with larger limbs.

This conservation of characters amongst all living terrestrial vertebrates is pretty powerful evidence for evolution having taken place, and that all of these diverse organisms developed through common descent from a single ancestor that first evolved this character.

Answer 2

Humans and birds have 4 legs!!?? Since when? Spiders have eight, bugs have 6, humans and birds have 2...so most of the creatures DON'T have 4!

Answer 3

because of the fact we developed that way. inspect some photos of lungfish. they have fins that are limblike, as they might bypass away the water for sessions of time (as their call shows). Fish do no longer in easy terms have 2 fins; they have some pairs, so those pairs ultimately grew to become the 4 limbs you spot on different creatures. Birds developed from dinosaurs (in certainty, birds are dinosaurs), which walked upright because of the fact their hips have sockets perpendicular to their femurs, yet all issues have 4 limbs. The creatures that stroll on all fours gain this because of the fact their bodies are based so as that one and all their legs touch the floor. it is for speed and stability; you do no longer see human beings outracing cheetahs or horses.

Answer 4

It's all about evoloution. Maybe fish did have legs before but they were found useless so as generations came, legs slowly disappeared. Humans evolved from apes. We didn't need much fur or a tail for we were too heavy to hang by a small tail. The less we use of a part, the part will soon disappear or grow small in size.

Answer 5

because, the four leg formula works well.. its an even base. its provides a great amount of balance Vs having 3 legs, and having five legs wouldnt give the animal much advantage if any.

How do humans and birds have four legs? four limbs yes..and fish, if you included their fins have four limbs.. HAHa i corrected you

Answer 6

most of the creatures in the world do not have four legs. you just think that because four-legged animals are the most common animals you see.

Answer 7

Most don't have four legs.

Insects have 6 legs.

Last I checked, birds don't have four legs either...

Answer 8

All land vertibrates have four legs, or at least the remanants of them because they share a common ancestor with four legs.