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PA55W0RD t1_j1yxjwm wrote

It is amazing to me that every land living or amphibious animal (including those that returned to water or took to air) that descended from the first fish that ventured onto land still have the basic 4 limb/5 fingers configuration.

That could have so easily have been 6 limbs/more fingers had our common ancestor have been different. Or changed somewhere along the way.... yet we share the same number of limbs/fingers with an amphibian with which our last common ancestor was 350 million years ago.

Edit: To clarify, I am only talking about the ancestors of the first tetrapod which evolved from tetrapod-like fish. Insects and other arthropods conquered land before us.

Many tetrapods have also lost digits and limbs on the way, birds, whales, snakes etc. None however have gained extra limbs or fingers as the norm, even though polydactyl gene mutations are quite common.

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Tifoid t1_j1z9zri wrote

What about snakes (no limbs), insects like centipedes and ants (more than 4 limbs), animals with hooves (no fingers)?

Guess you are right for land based mammals … but not “every land living or amphibious animal”.

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volpiousraccoon t1_j20fy0b wrote

It should be more like every tetrapod (four-limbed vertebrate that share ancestry with fish) has 4 limbs and 5-ish fingers configuration.

You are correct when you said that there are exceptions to this with some changes in fingers number and some animals with missing/vestigial limbs but the configuration it is generally true for most tetrapods. Some hooved mammals have one or two big fingers for their hooves because they evolved to loose their other digits over time. Marine mammals like whales are still considered therapods even though they do not really have back legs anymore but they still have the five finger configuration. Snakes are still considered tetrapod because their ancestors were reptiles that had all 4 limbs. It's kind of confusing and complicated, but generally the limb configuration is true for land-living vertebrates.

Insects and centipedes are not even vertebrates, so they do not have anatomy similar to tetrapods. It's kind of complicated but really cool to learn about once you get into it.

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TinTamarro t1_j1zjt5s wrote

Insects didn't descend fron fish?????

And snakes lost their limbs but their ancestors still had 4? And horses too?

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