a cool fact from dino class

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Here's a cool fact from Dino class.

When our fishy ancestors crawled out onto dry(er) land, their "limbs" were more like muscular fins than like arms and legs.  Eventually, they evolved arms and legs, and walked with a "sprawling stance" (legs out beyond the body, like lizards or alligators). After walking around in a "sprawling stance," two new lineages developed, one of which would eventually turn into birds, and the other into mammals.

Each of these new lineages separately and independently evolved an "upright (or erect) stance" (legs directly under the body, like cats, or humans).

Isn't that interesting?  That an erect stance was independently evolved in two different major lineages?  I always think that when the same trait evolves separately in different creatures and/or different places, that trait must be a really good idea.................

An erect stance is much more efficient for walking on land.  (Our lecturer mentioned how hard it would be to hold a "push-up position" with our arms out at right angles to our bodies, compared to just holding ourselves up on straight arms....)  Creatures with an erect stance spend less energy on standing and walking (on land) than do creatures with a sprawling stance.

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