Are there no land-based animals with uneven number of limbs?

[BeBMan]

At least there is no tripod-like creature or one with three or five arms I am aware of. Everything seems to be even-legged, even-armed? Does anyone know if there is some kind of evolutionary advantage behind this?

If so, does that mean bi-pedal space aliens in scifi aren't just a result of low budget, but rather of profound knowledge and research?

[Berzerker]

life should follow similar patterns and I suspect bipedal humanoids will be the dominant intelligence - sorry, no Starship Troopers wars with smart bugs. But the tail is the odd limb for many critters...

[OneFootInTheGrave]

[Al B. Sure!]

bilateral symmetry. That's why.

[Drake Tungsten]

I have three legs.

[Al B. Sure!]

As for alien bipedalism, Michael Shermer has this opinion on the issue (including Richard Dawkins' take):

http://www.scientificblogging.com/skeptic/michael_shermer_what_aliens_can_tell_us_about_evolution

[Berzerker]

how would people from another planet look? Would they be short and squat from more gravity, or tall and lanky from less gravity?

[ricketyclik]

Or tall and lanky from more gravity but also more buoyancy?

[Wernazuma III]

I have three legs.

What a surprise.

[MikeH]

OMG You are calling him a monkey because he's black?!

[Elok]

No, I think it's the throwing-feces bit.

[Dr Strangelove]

Intelligent creatures would need to be warm-blooded, to mainmtain a big energy sucking brain. They would need hands, there's no point in having that big brain unless you have hands to express its creativity. They would need two forward facing eyes with stereo vision with which to guide those hands. They would need a supple face, mouth and tongue with which to speak. We developed nearly hairless bodies with a patch of fur on top because our big brains drive us to generate a lot of heat because we're constantly active unlike our less brainy relatives. They would need a spine to stand upright in order to use their eyes and hands. So far intelligent creatures are looking rather humanoid. I suppose it's possible that land vertebrates might have devloped a basic six-legged plan instead of just four legs, in which case maybe an intelligent creature woule look like centaurs. On a planet with higher gravity the intelligent creature might be smaller. In a planet with less gravity there would be correspondingly less atmosphere, so creatures on a planet smaller than Earth would probably be smaller too.

[Al B. Sure!]

Dr. Strangelove:

Consider the Octopus, however:

Octopuses are highly intelligent, likely more so than any other order of invertebrates. The exact extent of their intelligence and learning capability is much debated among biologists, but maze and problem-solving experiments have shown that they do have both short- and long-term memory. Their short lifespans limit the amount they can ultimately learn. There has been much speculation to the effect that almost all octopus behaviors are independently learned rather than instinct-based, although this remains largely unproven. They learn almost no behaviors from their parents, with whom young octopuses have very little contact.

The octopus is the only invertebrate which has been conclusively shown to use tools. At least four specimens of the Veined Octopus (Amphioctopus marginatus) have been witnessed retrieving discarded coconut shells, manipulating them, and then reassembling them to use as shelter. This discovery was documented in the journal Current Biology and has also been caught on video.

Now, besides having quite a bit of intelligence, octopuses also have 'arms' which can manipulate things and they have color vision.

So the octopus definitely has the potential for intelligence even if they look nothing anthropomorphic.

[Elok]

There is no real reason why intelligent life couldn't develop underwater, no. Crows are pretty brilliant, too; all they'd need is a pair of manipulating digits somewhere in there, and they could also stand to be bigger. Really all you need is brain + appendages to apply your thoughts. The rest depends on environment.

[Al B. Sure!]

and Dr. Strangelove:

We developed nearly hairless bodies with a patch of fur on top because our big brains drive us to generate a lot of heat because we're constantly active unlike our less brainy relatives.

Are you saying the generation of heat caused hairlessness? I have never heard of that one. I thought the prevailing theory was the "Born to Run" theory or even the aquatic ape theory. There's also the idea that it was the result of sexual selection (less hair=less parasites=more attractive mate). There's a lot of ideas out there. Never heard of heat generation from the brain.