Did you know: All landliving bony animals descend from a shared four-limbed ancestor

In the distant past, a species of fish evolved from wholly aquatic to a mixed form, and from them descended amphibians, reptiles, birds and mammals. That is why most of them have four limbs (4 legs / 2 legs + 2 arms or wings), except for the few exceptions like snakes which transcended the need for legs.

Whales and Dolphins are aquatic mamals, but descend from landliving animals that returned to the sea. Perhaps the fact that that was easily possible for mammals, who were already quite long removed from the first land animals, is another sign of how heavily our construction is still based on theirs.

And make no mistake, the build of our bodies is in many ways just a tweaked version of features that were there from the very start. Among the most fundamental being the spinal column made of vertebrae - which is what gives us the group name of "vertebrates" - and the four-limbed thing I mentioned before.

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Finding out about the above made me think about how straight up all of the large land animals in the current time are vertebrates. It was only in the distant past that invertebrates (~bugs) were properly big. Nowadays its just our cousins - though maybe calling them cousins is exaggerating the closeness of the relation between us and a giant python too much.

If I remember correctly, this is because invertebrates are much more reliant on oxigen concentration in the air due to not having lungs. Us vertebrates and use the frame of our skeleton and our muscles to pull air into our lungs, then push it out again, creating high frequency circulation. But bugs just have lots of small air tubes throughout their body and rely on air dissipation to breathe. Therefore, no ability to manually increase oxygen intake.

Without that one instance of overly ambitious fish claiming land for the first time, how different would the world be? Would there just not be any other vertebrates on land, or would some other species have filled in that niche, that never got the opportunity in our timeline.

So many points in history when things could have easily ended up completely different...

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This post was based on the book "Endless Forms most Beautiful" by Sean B. Carroll

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This post was sponsored by Scientia Mundi, your one stop shop for the sciences.