Foot: Weight-bearing anatomical structure found in vertebrates
Land vertebrates have feet.
The organization of their feet varies. Two factors come into play: weight and lifestyle.
1. Plantigrade: heavy animals usually put their heels down to support their weight.
2. Unguligrade: large animals with hooves.
3. Digitigrade is usually reserved for lighter animals. It means to walk on the toes.
Walking
Most heavy animals walk on four legs. There are some exceptions. Some really heavy birds move or moved on two legs. Moas are one example and ostriches run very well on two legs.
Birds generally are an example of the change from quadruped walk (originally as dinosaurs), to bipedalism. Humans are also examples of changes that started in arboreal apes.
The study of such things is called "comparative foot morphology".
References
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