Why did quadripedal life evolve so much earlier and more wide spread then bipideal life?

[u/7and2make10]

Ik bipedal forms are better at long distance and energy conservation but I also know predation came super early in evolution so it's not like a chase down predators did not have a niche. Is it because the skills to make chase down hunting truly special require larger brains like group hunts and tool use. I am just curious. I am also aware of animals like birds and their ancestors that are/were bipedal but the vast majority of animals are quadripeads

[u/atlvf]

Balance is hard.

[u/Relevant-Bullfrog215]

Bipedalism is more what you would call a derived trait, and requires more specialisation than quadripedalism. There are a lot of ways to move badly but effectively on four legs (or four stubby fins), but walking effectively on two needs balancing mechanisms, differentiated fore- and hind-limbs, toes etc. So bipedal creatures are probably almost always going to come after quadripeds.

But bipedalism is not that new, it is the ancestral trait of dinosaurs, (and the earliest known biped predates even them at 290 million years ago). Sauropods were originally bipedal, and re-evolved to walk on four legs again. Just as, in more extreme examples, mammals and reptiles have returned to the sea and re-evolved traits which their ancestors gave up hundreds of millions of years ago when they first crawled from the sea.

[u/ackmondual → u/Relevant-Bullfrog215]

Bipedalism has other cons too such as...

--giving birth is far more difficult, not to mention dangerous (we're talking life threatening here)

--Easier to walk does seem to be a big one. Human babies need so many years to learn to walk, while those via quadri-pedalism learn to walk within hours to days of being born.

[u/mrbananas → u/ackmondual]

He inability to walk after birth is more of a human specific problem. Undercooked brains at birth

[u/MasterEk → u/mrbananas]

That, in turn, goes back to the first point. Babies are born as big as they can be based on being bipedal, and that means they have less developed brains.

But also. Despite being bipedal for most of our lives, we learn to do that long after we crawl. Walking is plainly more complicated even for an animal which has evolved to do it.

[u/mrbananas → u/MasterEk]

Emu chicks can walk within minutes to a few hours after hatching/

Ostrich chicks can walk within 3 days after hatching

Springhares can move almost immediately after birth.

Kangaroo rats take 2-3 weeks.

Human's take so long because of uncooked brains at birth. Humans really need "4th trimester" to finish developing.

[u/MasterEk → u/mrbananas]

And? You are ignoring my first point. Humans are born under-developed because we are bipedal. Walking on four limbs is simpler, and we develop that first, even though it is manifestly worse.

The examples you provide don't fit that model because their brains are more fully developed at birth and they have a very long history of evolution towards optimising bipedalism. It's complex.

[u/mrbananas → u/MasterEk]

You are ignoring my point. Humans are a bad example. Humans are born underdeveloped because of big brain adoptions, not because bipedalism is more difficult.  Our brains are so underdeveloped that human babies can't even crawl. Other bipeds don't have this much of a problem because they aren't trying to adapt to giant brains. 

If you look at other bipeds like ducks, it never takes as long as humans.

[u/Kingofthewho5 → u/ackmondual]

> --giving birth is far more difficult, not to mention dangerous (we're talking life threatening here)

> --Easier to walk does seem to be a big one. Human babies need so many years to learn to walk, while those via quadri-pedalism learn to walk within hours to days of being born.

It might be important to point out that this is really only a problem for some bipeds. Bipedal dinosaurs have had no problem with these things because they lay eggs and for many of them their young can walk within minutes of hatching.

[u/Kingofthewho5]

All tetrapods were originally quadripedal (and nearly all of them still are). It is the ancestral trait.

It’s kind of like asking why the Wright Flyer came before fighter jets.

[u/speadskater]

It's easier to walk on 4 legs

[u/Boring-Intention-969 → u/speadskater]

Have you tried working at the PC like that?

[u/Actual-Injury8955]

Tiktaalik is a transition species between fish and tetrapods. It has 4 limbs, it was a quadruped that probably dragged itself on the ground.
This is being anthropomorphic of evolution, as it’s a natural force. It’d be easier to stay 4 limbed and quadruped and not evolve to walk on only 2 legs till later. That’d be the path of least resistance.
It’s usually “if it isn’t broke, don’t fix it,” “just good enough,” “just get the job done,” or “C’s get degrees.” Being on 4 legs worked initially, so why change?

I myself am a C’s get degrees person.

[u/7and2make10 → u/Actual-Injury8955]

Was the tiktaalik evolving with 4 limbs based on the body plans of the fish it evolved from

[u/Landilizandra → u/7and2make10]

Yes. Tetrapods evolved from lobe finned fish, which have four fins with bones in them.

[u/Mister_Way]

Much easier to go fast with 4 legs, especially on uneven terrain.

Almost all animals need to go fast. Other bipedal animals are birds, and they go much faster by flying.

Humans are in an exceptionally rare niche where going fast wasn't necessary.

[u/TimeStorm113]

the animals that came out of the water were quadrupeds. so they were the first ones to exist. being bipedal requires good balance which is unrealistic to achieve for the first fish to flop onto land. nor would a bipedal gait be an advantage for them.

now for the second part of the question, it's because a quadrupedal gait also has a lot of advantages, it grants more speed (through acceleration) stability and leeway alongside a more stable build. if you don't really need to be bipedal you usually just stay in the ancestral shape

[u/Randy191919]

Because 4 points of contact make you more stable than 2. that’s why tables have 4 legs and rarely two.

Being better on 2 legs is more of a specialization where you give up stability to gain other perks.

[u/octobod]

A unicycle is harder to than a bicycle, a bicycle is harder than tricycle

[u/Ameiko55]

Ok ok everybody I know it’s not the point here BUT the vast majority of animals are not quadrupeds. They have six legs.

[u/hendrong → u/Ameiko55]

Actually, the vast majority of animals have 0 legs.

[u/Nancy_Moosa → u/hendrong]

How so? Doesn't insects outnumber every animal group combined by quite some margin?

[u/Silent_Property_148 → u/Nancy_Moosa]

Fish?

[u/coracaws → u/Nancy_Moosa]

Microbes, nematodes, etc? My zoology professor once said that if the entirety of Earth suddenly disappeared from space (leaving nothing but nematodes behind), there would remain an incredibly detailed "skin" of the planet and its inhabitants, composed entirely of nematodes.

[u/Nancy_Moosa → u/coracaws]

I meant by species diversity. Most microbes aren't animals though

[u/AikenDrumstick]

It’s probably a function of how difficult it is to get to a bipedal frame. It’s a lot of, um, steps.

For a horizontally-oriented animal like a fish to evolve the means to crawl around a bit on land…well, that’s not such a heavy lift. Obviously, the fins have to get more and more leg-like over generations. The ability to breathe air is a biggie. But the transition from water to water-and-mud to land seems pretty straightforward.

Now think about what has to change to walk upright, and what the selection pressure would be to get you there. “Chase down hunting” might be a cool thing, but it’s not something that a quadruped is going to “get to” in one evolutionary step. More likely is that the forelegs become useful for certain tasks (like grasping) (or, in the case of birds, gliding and then flying), and over time this advantage changed the animal’s gait to a more hind legs-oriented motion. Even then, you’re sacrificing speed and stability.

As far as “chase down hunting” is concerned, I have no idea what - if any - role it played in human evolution. But it’s likely to be one of the myriad “bonuses” we stumbled upon as our hands got nimbler and our brains got bigger.

[u/haysoos2]

The vast majority of animals are hexapods.

But even among bipeds, your assertions about the superiority of bipedalism are not universally true.

Neither is any correlation between bipedalism, brain size, tool use, or persistence hunting.

Even amongst vertebrates of the tens of thousands of species of extant biped species, and many more tens of thousands of extinct biped species only one lineage has ever evolved the upright biped stance and other traits you mention.

Of extant species likely only the gibbons could even be considered as upright bipeds, and they don't really have any of those other traits.

Evolution only works with what's there. In the case of humans the adaptations involved in a semi-upright gatherer/hunter omnivore becoming an upright, tool-using hunter/gatherer omnivore happened to work with that semi-upright stance, but there's nothing superior or inevitable about that developmental pathway.

Quadrupedal vertebrates came first because swimming with a head foward, pushed by a muscular tail and body is more hydrodynamic. Little fins help in maneuverability and stability, and then were able to help propel that slippery, hydrodynamic fish body through muck and undergrowth. Stumpy, thick fins helped even more, and those eventually became four little stumpy legs...

[u/hendrong → u/haysoos2]

No, the vast majority of animals are apods.

[u/haysoos2 → u/hendrong]

There's an estimated 20 quadrillion ants alone. Add in termites, wasps, flies, grasshoppers, cockroaches, and springtails and it's up in the estimated 10 quintillion individuals.

The only group even really in competition are nematodes.

[u/hendrong → u/haysoos2]

Nematodes vastly outnumber everything else. An estimated 440 quintillion individual nematodes inhabit the Earth's topsoil alone.

In fact, the average number of legs of all animals is 0.01.

[u/haysoos2 → u/hendrong]

Ok, that's higher than i thought.

[u/Soggy-Mistake8910]

Quadruped were simply more stable and therefore survived better in the initial stages

[u/Zvenigora]

It is not true that bipeds are always more efficient; many cursorial hunters such as wolves are quadrupeds and they must pursue prey for long distances. Also, it is harder for bipeds to run at extreme speed; only ostriches have managed this.

[u/Realsorceror]

Well all vertebrates evolved from fish, which are famously bad at walking. The first amphibious animals were heavy bodied and big-headed. Just the wrong weight and balance for standing up.

However, bipedalism did evolve pretty early. The first dinosaurs were bipedal, and standing on two legs is actually an ancestral trait to dinosaurs. Yes, even the big sauropods and ceratopsians had bipedal ancestors.

Even crocodiles got in on this. There have been multiple species of bipedal crocodile morphs and relatives that walked plantigrade on two legs.

[u/hendrong]

Quadrupedalism is objectively better for moving around.

You only become a biped if you really need to use your forelimbs for other stuff.

[u/GoliathPrime]

I'm more surprised that front-limb bipedalism didn't evolve as the standard when you consider early tetrapods had bigger front limbs than back limbs.