Eight-Armed Animal Preceded Dinosaurs

Garimelda writes "Scientists have discovered what they believe is an eight-armed creature which colonized a large section of the world's oceans over 300 million years before the first dinosaurs emerged."

Re:FSM

[jemtallon]

Check those noodly appendages... intelligent design indeed!

Just further proof that the Flying Spaghetti Monster's [flyingspag...onster.com] great tentacle guides us all across the saucy plate of life

Re:computer evolution experiments

[Danny Rathjens]

Here they are. He has some pretty cool videos showing the different types of locomotion that resulted. I love the one that grows really tall and falls over; it certainly achieved some fast movement over a short distance - but a bit of an evolutionary dead end. :)
http://www.karlsims.com/evolved-virtual-creatures.html [karlsims.com]

Re:four accidental or metabolically efficient?

[Bowling Moses]

We don't have 5-fold symmetry. We're bilaterally symmetric [wikipedia.org]; we have a top, bottom, left, and right. A starfish has a top and bottom, but no left or right. For what it's worth, not even a five-armed starfish has exactly 5-fold symmetry. They are considered radially symmetric, but are thought to have evolved from bilaterally symmetric organisms and have some structures that show this.

Re:Eight-armed creature

[theaveng]

This animal is more like a hydra with multiple tentacles but extremely small and simplistic in design.

BTW there were LOTS of creatures that came before the dinosaurs.

There were the Cambrian creatures, followed by the Synapsids that were huge reptile-like creatures that dominated the planet until they were eventually replaced the dinosaurs. The Synapsids then evolved into mammals - http://en.wikipedia.org/wiki/Synapsid [wikipedia.org] For more info see the BBC's "Before the Dinosaurs"

Not the same kind of limb

[Moraelin]

1. Well, you have to also realize that different environments might favour different configurations. For example an octopus doesn't use its noodly appendages in the same way as you use your legs, and not even like a fish uses its fins.

Each is optimized for its particular use. It's safe to assume that for a fish that particular tail and fin configuration is good, because it evolved several times from something different to that exact configuration. E.g., dolphins evolved to the same scheme, but so did Ichthyosaurs, Plesiosaurs and Mosasaurs, plus a few of their relatives and ancestors. There are two different configurations of four legs which evolved into such a fish-like configuration that Ichthyosaur skeletons were first believed to be fish. So it's safe to assume that for that style of swimming, a fish-like configuration is optimal, and indeed better than four legs or even than two legs.

Two legs vs four legs also seems to be not that clear cut. The two-legged configuration evolved independently more than once, so it must have _some_ advantages. E.g., all dinosaurs are descendants of a two-legged ancestor. Some, however, returned to four-legged afterwards. Some evolved into birds instead. So again it's probably safe to say that each is good... for a given environment.

Insects are a funny case, because again they're used differently than you use your legs. Insect legs are autonomous. Each leg has its own autonomous "controller", or rather its own mini-brain. The insect's head just gives an order like "forward" and all legs independently start doing the movements for moving forward. That kind of a wiring would be totally unfit for bipedal use. Heck, even four would be more miss than hit. So an insect must necessarily have a larger number of legs. For the way an insect is built, really, six legs are good, two legs are bad.

2. But even that is over-thinking it, because the little guys in TFA didn't actually have arms or legs like you. They were really jellyfish with 8 long tubular appendages. There are no muscles there or bones or exoskeleton or anything usable for locomotion at all. The whole thing was really two thin layers of cells, little more than a microbial film, with an amorphous jelly in between. The "arms" were probably more to give it more surface and reach from which it can absorb nutrients, than for anything else.

We're talking _very_ primitive multi-cellular life forms.

Re:four accidental or metabolically efficient?

[Five Bucks!]

Tetrapods don't quite represent 5-fold symmetry.

Think of the tailbone to top-of-skull as a single axis, with two sets of limbs poking out along the axis.

This developed from the pelvic and pectoral girdles of Sarcopterygians.

Basically, the whole vertebral column from tail to cervical vertebrae is the principle axis with limbs branching from it. Split down the middle of the principle axis, the body (for the most party) is a mirror image. Thus, two-fold symmetry. Bilateralism.

Tetrapodia [wikipedia.org]
5-Fold symmetry [wikipedia.org]